diff --git a/toolchain/check/convert.cpp b/toolchain/check/convert.cpp
index 9d3147969de7..138b2b9a2722 100644
--- a/toolchain/check/convert.cpp
+++ b/toolchain/check/convert.cpp
@@ -264,7 +264,7 @@ static auto ConvertTupleToArray(Context& context, SemIR::TupleType tuple_type,
 
   // Check that the tuple is the right size.
   std::optional<uint64_t> array_bound =
-      sem_ir.GetArrayBoundValue(array_type.bound_id);
+      sem_ir.GetZExtIntValue(array_type.bound_id);
   if (!array_bound) {
     // TODO: Should this fall back to using `ImplicitAs`?
     if (target.diagnose) {
diff --git a/toolchain/check/cpp/import.cpp b/toolchain/check/cpp/import.cpp
index 842bf075e8fc..57648edf82f8 100644
--- a/toolchain/check/cpp/import.cpp
+++ b/toolchain/check/cpp/import.cpp
@@ -64,6 +64,7 @@
 #include "toolchain/sem_ir/inst.h"
 #include "toolchain/sem_ir/name_scope.h"
 #include "toolchain/sem_ir/pattern.h"
+#include "toolchain/sem_ir/type_info.h"
 #include "toolchain/sem_ir/typed_insts.h"
 
 namespace Carbon::Check {
@@ -450,14 +451,16 @@ static auto ImportClassObjectRepr(Context& context, SemIR::ClassId class_id,
   const auto& clang_layout =
       context.ast_context().getASTRecordLayout(clang_def);
 
-  llvm::SmallVector<uint64_t> layout;
+  llvm::SmallVector<SemIR::ObjectSize> layout;
   llvm::SmallVector<SemIR::StructTypeField> fields;
 
   static_assert(SemIR::CustomLayoutId::SizeIndex == 0);
-  layout.push_back(clang_layout.getSize().getQuantity());
+  layout.push_back(
+      SemIR::ObjectSize::Bytes(clang_layout.getSize().getQuantity()));
 
   static_assert(SemIR::CustomLayoutId::AlignIndex == 1);
-  layout.push_back(clang_layout.getAlignment().getQuantity());
+  layout.push_back(
+      SemIR::ObjectSize::Bytes(clang_layout.getAlignment().getQuantity()));
 
   static_assert(SemIR::CustomLayoutId::FirstFieldIndex == 2);
 
@@ -529,7 +532,7 @@ static auto ImportClassObjectRepr(Context& context, SemIR::ClassId class_id,
     auto base_offset = base.isVirtual()
                            ? clang_layout.getVBaseClassOffset(base_class)
                            : clang_layout.getBaseClassOffset(base_class);
-    layout.push_back(base_offset.getQuantity());
+    layout.push_back(SemIR::ObjectSize::Bytes(base_offset.getQuantity()));
     fields.push_back(
         {.name_id = SemIR::NameId::Base, .type_inst_id = base_type_inst_id});
   }
@@ -602,8 +605,7 @@ static auto ImportClassObjectRepr(Context& context, SemIR::ClassId class_id,
       offset += inner_layout.getFieldOffset(inner_field->getFieldIndex());
     }
 
-    layout.push_back(
-        context.ast_context().toCharUnitsFromBits(offset).getQuantity());
+    layout.push_back(SemIR::ObjectSize::Bits(offset));
     fields.push_back(
         {.name_id = field_name_id, .type_inst_id = field_type_inst_id});
   }
diff --git a/toolchain/check/custom_witness.cpp b/toolchain/check/custom_witness.cpp
index b43d9b3a851b..25ce07283f13 100644
--- a/toolchain/check/custom_witness.cpp
+++ b/toolchain/check/custom_witness.cpp
@@ -200,7 +200,7 @@ static auto CanDestroyType(
     case CARBON_KIND(SemIR::ArrayType array_type): {
       // A zero element array is always trivially destructible.
       if (auto int_bound =
-              context.sem_ir().GetArrayBoundValue(array_type.bound_id);
+              context.sem_ir().GetZExtIntValue(array_type.bound_id);
           !int_bound || *int_bound == 0) {
         return DestroyFormat::Trivial;
       }
diff --git a/toolchain/check/testdata/basics/raw_sem_ir/builtins.carbon b/toolchain/check/testdata/basics/raw_sem_ir/builtins.carbon
index fee94cb616ad..233930b4ab69 100644
--- a/toolchain/check/testdata/basics/raw_sem_ir/builtins.carbon
+++ b/toolchain/check/testdata/basics/raw_sem_ir/builtins.carbon
@@ -37,12 +37,24 @@
 // CHECK:STDOUT:   types:
 // CHECK:STDOUT:     'type(TypeType)':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(TypeType)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst(FormType))':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(inst(FormType))}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(Error)':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(Error)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst(NamespaceType))':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(inst(NamespaceType))}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:   facet_types:     {}
 // CHECK:STDOUT:   insts:
 // CHECK:STDOUT:     'inst(TypeType)':  {kind: TypeType, type: type(TypeType)}
diff --git a/toolchain/check/testdata/basics/raw_sem_ir/cpp_interop.carbon b/toolchain/check/testdata/basics/raw_sem_ir/cpp_interop.carbon
index 4871c9631bb2..8d612519b3bb 100644
--- a/toolchain/check/testdata/basics/raw_sem_ir/cpp_interop.carbon
+++ b/toolchain/check/testdata/basics/raw_sem_ir/cpp_interop.carbon
@@ -96,38 +96,89 @@ fn G(x: Cpp.X) {
 // CHECK:STDOUT:   types:
 // CHECK:STDOUT:     'type(TypeType)':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(TypeType)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst(FormType))':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(inst(FormType))}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(Error)':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(Error)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst(NamespaceType))':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(inst(NamespaceType))}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst(InstType))':
 // CHECK:STDOUT:       value_repr:      {kind: none, type: type(inst50000013)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst50000013)':
 // CHECK:STDOUT:       value_repr:      {kind: none, type: type(inst50000013)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst5000001E)':
 // CHECK:STDOUT:       value_repr:      {kind: none, type: type(inst50000013)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst50000020)':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(inst50000020)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            8
+// CHECK:STDOUT:         alignment:       8
 // CHECK:STDOUT:     'type(inst(WitnessType))':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(inst(WitnessType))}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst50000027)':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(inst50000027)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            8
+// CHECK:STDOUT:         alignment:       8
 // CHECK:STDOUT:     'type(inst50000024)':
 // CHECK:STDOUT:       value_repr:      {kind: pointer, type: type(inst50000027)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            8
+// CHECK:STDOUT:         alignment:       8
 // CHECK:STDOUT:     'type(inst50000015)':
 // CHECK:STDOUT:       value_repr:      {kind: pointer, type: type(inst50000027)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            8
+// CHECK:STDOUT:         alignment:       8
 // CHECK:STDOUT:     'type(inst50000029)':
 // CHECK:STDOUT:       value_repr:      {kind: none, type: type(inst50000013)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst5000002E)':
 // CHECK:STDOUT:       value_repr:      {kind: none, type: type(inst50000013)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst50000031)':
 // CHECK:STDOUT:       value_repr:      {kind: none, type: type(inst50000013)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst5000003C)':
 // CHECK:STDOUT:       value_repr:      {kind: none, type: type(inst50000013)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst50000044)':
 // CHECK:STDOUT:       value_repr:      {kind: none, type: type(inst50000013)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:   facet_types:     {}
 // CHECK:STDOUT:   insts:
 // CHECK:STDOUT:     'inst(TypeType)':  {kind: TypeType, type: type(TypeType)}
diff --git a/toolchain/check/testdata/basics/raw_sem_ir/multifile.carbon b/toolchain/check/testdata/basics/raw_sem_ir/multifile.carbon
index 552c5662595f..068cacbe0763 100644
--- a/toolchain/check/testdata/basics/raw_sem_ir/multifile.carbon
+++ b/toolchain/check/testdata/basics/raw_sem_ir/multifile.carbon
@@ -55,16 +55,34 @@ fn B() {
 // CHECK:STDOUT:   types:
 // CHECK:STDOUT:     'type(TypeType)':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(TypeType)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst(FormType))':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(inst(FormType))}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(Error)':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(Error)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst(NamespaceType))':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(inst(NamespaceType))}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst50000011)':
 // CHECK:STDOUT:       value_repr:      {kind: none, type: type(inst50000012)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst50000012)':
 // CHECK:STDOUT:       value_repr:      {kind: none, type: type(inst50000012)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:   facet_types:     {}
 // CHECK:STDOUT:   insts:
 // CHECK:STDOUT:     instF:           {kind: Namespace, arg0: name_scope0, arg1: inst<none>, type: type(inst(NamespaceType))}
@@ -138,18 +156,39 @@ fn B() {
 // CHECK:STDOUT:   types:
 // CHECK:STDOUT:     'type(TypeType)':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(TypeType)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst(FormType))':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(inst(FormType))}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(Error)':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(Error)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst(NamespaceType))':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(inst(NamespaceType))}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst70000013)':
 // CHECK:STDOUT:       value_repr:      {kind: none, type: type(inst70000014)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst70000014)':
 // CHECK:STDOUT:       value_repr:      {kind: none, type: type(inst70000014)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst(InstType))':
 // CHECK:STDOUT:       value_repr:      {kind: none, type: type(inst70000014)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:   facet_types:     {}
 // CHECK:STDOUT:   insts:
 // CHECK:STDOUT:     instF:           {kind: Namespace, arg0: name_scope0, arg1: inst<none>, type: type(inst(NamespaceType))}
diff --git a/toolchain/check/testdata/basics/raw_sem_ir/multifile_with_textual_ir.carbon b/toolchain/check/testdata/basics/raw_sem_ir/multifile_with_textual_ir.carbon
index 08d089b98584..4d9c74aef516 100644
--- a/toolchain/check/testdata/basics/raw_sem_ir/multifile_with_textual_ir.carbon
+++ b/toolchain/check/testdata/basics/raw_sem_ir/multifile_with_textual_ir.carbon
@@ -55,16 +55,34 @@ fn B() {
 // CHECK:STDOUT:   types:
 // CHECK:STDOUT:     'type(TypeType)':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(TypeType)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst(FormType))':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(inst(FormType))}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(Error)':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(Error)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst(NamespaceType))':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(inst(NamespaceType))}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst50000011)':
 // CHECK:STDOUT:       value_repr:      {kind: none, type: type(inst50000012)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst50000012)':
 // CHECK:STDOUT:       value_repr:      {kind: none, type: type(inst50000012)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:   facet_types:     {}
 // CHECK:STDOUT:   insts:
 // CHECK:STDOUT:     instF:           {kind: Namespace, arg0: name_scope0, arg1: inst<none>, type: type(inst(NamespaceType))}
@@ -157,18 +175,39 @@ fn B() {
 // CHECK:STDOUT:   types:
 // CHECK:STDOUT:     'type(TypeType)':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(TypeType)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst(FormType))':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(inst(FormType))}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(Error)':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(Error)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst(NamespaceType))':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(inst(NamespaceType))}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst70000013)':
 // CHECK:STDOUT:       value_repr:      {kind: none, type: type(inst70000014)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst70000014)':
 // CHECK:STDOUT:       value_repr:      {kind: none, type: type(inst70000014)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst(InstType))':
 // CHECK:STDOUT:       value_repr:      {kind: none, type: type(inst70000014)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:   facet_types:     {}
 // CHECK:STDOUT:   insts:
 // CHECK:STDOUT:     instF:           {kind: Namespace, arg0: name_scope0, arg1: inst<none>, type: type(inst(NamespaceType))}
diff --git a/toolchain/check/testdata/basics/raw_sem_ir/one_file.carbon b/toolchain/check/testdata/basics/raw_sem_ir/one_file.carbon
index 3b1b891e6e42..596f0faba9cc 100644
--- a/toolchain/check/testdata/basics/raw_sem_ir/one_file.carbon
+++ b/toolchain/check/testdata/basics/raw_sem_ir/one_file.carbon
@@ -417,46 +417,109 @@ fn Foo[T:! type](p: T*) -> (T*, ()) {
 // CHECK:STDOUT:   types:
 // CHECK:STDOUT:     'type(TypeType)':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(TypeType)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst(FormType))':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(inst(FormType))}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(Error)':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(Error)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst(NamespaceType))':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(inst(NamespaceType))}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst78000026)':
 // CHECK:STDOUT:       value_repr:      {kind: none, type: type(inst78000026)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst7800002D)':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(inst7800002D)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            8
+// CHECK:STDOUT:         alignment:       8
 // CHECK:STDOUT:     'type(inst78000029)':
 // CHECK:STDOUT:       value_repr:      {kind: pointer, type: type(inst7800002D)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst7800003F)':
 // CHECK:STDOUT:       value_repr:      {kind: none, type: type(inst78000026)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(symbolic_constant78000003)':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(symbolic_constant78000003)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            8
+// CHECK:STDOUT:         alignment:       8
 // CHECK:STDOUT:     'type(inst(WitnessType))':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(inst(WitnessType))}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(symbolic_constant78000011)':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(symbolic_constant78000011)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            8
+// CHECK:STDOUT:         alignment:       8
 // CHECK:STDOUT:     'type(symbolic_constant78000009)':
 // CHECK:STDOUT:       value_repr:      {kind: pointer, type: type(symbolic_constant78000011)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            8
+// CHECK:STDOUT:         alignment:       8
 // CHECK:STDOUT:     'type(symbolic_constant78000004)':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(symbolic_constant78000004)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            8
+// CHECK:STDOUT:         alignment:       8
 // CHECK:STDOUT:     'type(symbolic_constant7800000A)':
 // CHECK:STDOUT:       value_repr:      {kind: pointer, type: type(symbolic_constant78000011)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            8
+// CHECK:STDOUT:         alignment:       8
 // CHECK:STDOUT:     'type(inst(InstType))':
 // CHECK:STDOUT:       value_repr:      {kind: none, type: type(inst78000026)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst78000050)':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(inst78000050)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst(SpecificFunctionType))':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(inst(SpecificFunctionType))}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst(RequireSpecificDefinitionType))':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(inst(RequireSpecificDefinitionType))}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(symbolic_constant78000145)':
 // CHECK:STDOUT:       value_repr:      {kind: none, type: type(inst78000026)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(symbolic_constant7800014A)':
 // CHECK:STDOUT:       value_repr:      {kind: none, type: type(inst78000026)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst(BoundMethodType))':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(inst(BoundMethodType))}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:   facet_types:
 // CHECK:STDOUT:     facet_type78000000: {}
 // CHECK:STDOUT:     facet_type78000001: {extends interface: interface78000000}
diff --git a/toolchain/check/testdata/basics/raw_sem_ir/one_file_with_textual_ir.carbon b/toolchain/check/testdata/basics/raw_sem_ir/one_file_with_textual_ir.carbon
index 4d257b73d801..942f664a8aea 100644
--- a/toolchain/check/testdata/basics/raw_sem_ir/one_file_with_textual_ir.carbon
+++ b/toolchain/check/testdata/basics/raw_sem_ir/one_file_with_textual_ir.carbon
@@ -47,20 +47,44 @@ fn Foo(n: ()) -> ((), ()) {
 // CHECK:STDOUT:   types:
 // CHECK:STDOUT:     'type(TypeType)':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(TypeType)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst(FormType))':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(inst(FormType))}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(Error)':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(Error)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst(NamespaceType))':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(inst(NamespaceType))}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst50000010)':
 // CHECK:STDOUT:       value_repr:      {kind: none, type: type(inst50000010)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst5000001D)':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(inst5000001D)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            8
+// CHECK:STDOUT:         alignment:       8
 // CHECK:STDOUT:     'type(inst5000001A)':
 // CHECK:STDOUT:       value_repr:      {kind: pointer, type: type(inst5000001D)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst5000002B)':
 // CHECK:STDOUT:       value_repr:      {kind: none, type: type(inst50000010)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:   facet_types:     {}
 // CHECK:STDOUT:   insts:
 // CHECK:STDOUT:     instF:           {kind: Namespace, arg0: name_scope0, arg1: inst<none>, type: type(inst(NamespaceType))}
diff --git a/toolchain/check/testdata/interop/cpp/function/overloads.carbon b/toolchain/check/testdata/interop/cpp/function/overloads.carbon
index 65ad992c35d8..5d7ec58a58a0 100644
--- a/toolchain/check/testdata/interop/cpp/function/overloads.carbon
+++ b/toolchain/check/testdata/interop/cpp/function/overloads.carbon
@@ -2577,8 +2577,8 @@ fn F() {
 // CHECK:STDOUT:   %PassThreeFields__carbon_thunk.type: type = fn_type @PassThreeFields__carbon_thunk [concrete]
 // CHECK:STDOUT:   %PassThreeFields__carbon_thunk: %PassThreeFields__carbon_thunk.type = struct_value () [concrete]
 // CHECK:STDOUT:   %ThreeFields.elem: type = unbound_element_type %ThreeFields.942, %i32 [concrete]
-// CHECK:STDOUT:   %.c77: type = custom_layout_type {size=12, align=4, .a@0: %i32, .b@4: %i32, .c@8: %i32} [concrete]
-// CHECK:STDOUT:   %complete_type.702: <witness> = complete_type_witness %.c77 [concrete]
+// CHECK:STDOUT:   %.b0d: type = custom_layout_type {size=12, align=4, .a@0: %i32, .b@4: %i32, .c@8: %i32} [concrete]
+// CHECK:STDOUT:   %complete_type.54f: <witness> = complete_type_witness %.b0d [concrete]
 // CHECK:STDOUT:   %ImplicitAs.type.cc7: type = generic_interface_type @ImplicitAs [concrete]
 // CHECK:STDOUT:   %ImplicitAs.generic: %ImplicitAs.type.cc7 = struct_value () [concrete]
 // CHECK:STDOUT:   %struct_type.b.c.a: type = struct_type {.b: Core.IntLiteral, .c: Core.IntLiteral, .a: Core.IntLiteral} [concrete]
@@ -2669,8 +2669,8 @@ fn F() {
 // CHECK:STDOUT:   %i32.5: type = class_type @Int, @Int(constants.%int_32) [concrete = constants.%i32]
 // CHECK:STDOUT:   %i32.6: type = type_literal %i32.5 [concrete = constants.%i32]
 // CHECK:STDOUT:   %.3: %ThreeFields.elem = field_decl c, element2 [concrete]
-// CHECK:STDOUT:   %.4: type = custom_layout_type {size=12, align=4, .a@0: %i32, .b@4: %i32, .c@8: %i32} [concrete = constants.%.c77]
-// CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %.4 [concrete = constants.%complete_type.702]
+// CHECK:STDOUT:   %.4: type = custom_layout_type {size=12, align=4, .a@0: %i32, .b@4: %i32, .c@8: %i32} [concrete = constants.%.b0d]
+// CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %.4 [concrete = constants.%complete_type.54f]
 // CHECK:STDOUT:   complete_type_witness = %complete_type
 // CHECK:STDOUT:
 // CHECK:STDOUT: !members:
@@ -2880,8 +2880,8 @@ fn F() {
 // CHECK:STDOUT:   %PassThreeFields__carbon_thunk.type: type = fn_type @PassThreeFields__carbon_thunk [concrete]
 // CHECK:STDOUT:   %PassThreeFields__carbon_thunk: %PassThreeFields__carbon_thunk.type = struct_value () [concrete]
 // CHECK:STDOUT:   %ThreeFields.elem: type = unbound_element_type %ThreeFields.942, %i32 [concrete]
-// CHECK:STDOUT:   %.c77: type = custom_layout_type {size=12, align=4, .a@0: %i32, .b@4: %i32, .c@8: %i32} [concrete]
-// CHECK:STDOUT:   %complete_type.702: <witness> = complete_type_witness %.c77 [concrete]
+// CHECK:STDOUT:   %.b0d: type = custom_layout_type {size=12, align=4, .a@0: %i32, .b@4: %i32, .c@8: %i32} [concrete]
+// CHECK:STDOUT:   %complete_type.54f: <witness> = complete_type_witness %.b0d [concrete]
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: imports {
@@ -3020,8 +3020,8 @@ fn F() {
 // CHECK:STDOUT:   %i32.5: type = class_type @Int, @Int(constants.%int_32) [concrete = constants.%i32]
 // CHECK:STDOUT:   %i32.6: type = type_literal %i32.5 [concrete = constants.%i32]
 // CHECK:STDOUT:   %.3: %ThreeFields.elem = field_decl c, element2 [concrete]
-// CHECK:STDOUT:   %.4: type = custom_layout_type {size=12, align=4, .a@0: %i32, .b@4: %i32, .c@8: %i32} [concrete = constants.%.c77]
-// CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %.4 [concrete = constants.%complete_type.702]
+// CHECK:STDOUT:   %.4: type = custom_layout_type {size=12, align=4, .a@0: %i32, .b@4: %i32, .c@8: %i32} [concrete = constants.%.b0d]
+// CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %.4 [concrete = constants.%complete_type.54f]
 // CHECK:STDOUT:   complete_type_witness = %complete_type
 // CHECK:STDOUT:
 // CHECK:STDOUT: !members:
@@ -3344,11 +3344,11 @@ fn F() {
 // CHECK:STDOUT:   %Int.generic: %Int.type = struct_value () [concrete]
 // CHECK:STDOUT:   %i32: type = class_type @Int, @Int(%int_32) [concrete]
 // CHECK:STDOUT:   %B.elem.c76: type = unbound_element_type %B, %i32 [concrete]
-// CHECK:STDOUT:   %.e7f: type = custom_layout_type {size=12, align=4, .a@0: %A, .n@8: %i32} [concrete]
-// CHECK:STDOUT:   %complete_type.b39: <witness> = complete_type_witness %.e7f [concrete]
+// CHECK:STDOUT:   %.344: type = custom_layout_type {size=12, align=4, .a@0: %A, .n@8: %i32} [concrete]
+// CHECK:STDOUT:   %complete_type.e04: <witness> = complete_type_witness %.344 [concrete]
 // CHECK:STDOUT:   %A.elem: type = unbound_element_type %A, %i32 [concrete]
-// CHECK:STDOUT:   %.7b6: type = custom_layout_type {size=8, align=4, .x@0: %i32, .y@4: %i32} [concrete]
-// CHECK:STDOUT:   %complete_type.1e0: <witness> = complete_type_witness %.7b6 [concrete]
+// CHECK:STDOUT:   %.171: type = custom_layout_type {size=8, align=4, .x@0: %i32, .y@4: %i32} [concrete]
+// CHECK:STDOUT:   %complete_type.2e6: <witness> = complete_type_witness %.171 [concrete]
 // CHECK:STDOUT:   %ImplicitAs.type.cc7: type = generic_interface_type @ImplicitAs [concrete]
 // CHECK:STDOUT:   %ImplicitAs.generic: %ImplicitAs.type.cc7 = struct_value () [concrete]
 // CHECK:STDOUT: }
@@ -3395,8 +3395,8 @@ fn F() {
 // CHECK:STDOUT:   %i32.1: type = class_type @Int, @Int(constants.%int_32) [concrete = constants.%i32]
 // CHECK:STDOUT:   %i32.2: type = type_literal %i32.1 [concrete = constants.%i32]
 // CHECK:STDOUT:   %.2: %B.elem.c76 = field_decl n, element1 [concrete]
-// CHECK:STDOUT:   %.3: type = custom_layout_type {size=12, align=4, .a@0: %A, .n@8: %i32} [concrete = constants.%.e7f]
-// CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %.3 [concrete = constants.%complete_type.b39]
+// CHECK:STDOUT:   %.3: type = custom_layout_type {size=12, align=4, .a@0: %A, .n@8: %i32} [concrete = constants.%.344]
+// CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %.3 [concrete = constants.%complete_type.e04]
 // CHECK:STDOUT:   complete_type_witness = %complete_type
 // CHECK:STDOUT:
 // CHECK:STDOUT: !members:
@@ -3412,8 +3412,8 @@ fn F() {
 // CHECK:STDOUT:   %i32.3: type = class_type @Int, @Int(constants.%int_32) [concrete = constants.%i32]
 // CHECK:STDOUT:   %i32.4: type = type_literal %i32.3 [concrete = constants.%i32]
 // CHECK:STDOUT:   %.2: %A.elem = field_decl y, element1 [concrete]
-// CHECK:STDOUT:   %.3: type = custom_layout_type {size=8, align=4, .x@0: %i32, .y@4: %i32} [concrete = constants.%.7b6]
-// CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %.3 [concrete = constants.%complete_type.1e0]
+// CHECK:STDOUT:   %.3: type = custom_layout_type {size=8, align=4, .x@0: %i32, .y@4: %i32} [concrete = constants.%.171]
+// CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %.3 [concrete = constants.%complete_type.2e6]
 // CHECK:STDOUT:   complete_type_witness = %complete_type
 // CHECK:STDOUT:
 // CHECK:STDOUT: !members:
diff --git a/toolchain/check/type_completion.cpp b/toolchain/check/type_completion.cpp
index cc7d79b29e65..1744f7ea8f52 100644
--- a/toolchain/check/type_completion.cpp
+++ b/toolchain/check/type_completion.cpp
@@ -222,12 +222,14 @@ class TypeCompleter {
   // `type_inst` to be complete to our work list.
   auto AddNestedIncompleteTypes(SemIR::Inst type_inst) -> bool;
 
-  // Makes an empty value representation, which is used for types that have no
-  // state, such as empty structs and tuples.
-  auto MakeEmptyValueRepr() const -> SemIR::ValueRepr;
+  // Makes type info for a type with an empty value representation, which is
+  // used for types that have no state, such as empty structs and tuples.
+  auto MakeEmptyTypeInfo() const -> SemIR::CompleteTypeInfo;
 
-  // Makes a dependent value representation, which is used for symbolic types.
-  auto MakeDependentValueRepr(SemIR::TypeId type_id) const -> SemIR::ValueRepr;
+  // Makes type info for a type with a dependent value representation, which is
+  // used for symbolic types.
+  auto MakeDependentTypeInfo(SemIR::TypeId type_id) const
+      -> SemIR::CompleteTypeInfo;
 
   // Makes a value representation that uses pass-by-copy, copying the given
   // type.
@@ -243,25 +245,34 @@ class TypeCompleter {
                                 SemIR::ValueRepr::NotAggregate) const
       -> SemIR::ValueRepr;
 
-  // Gets the value representation of a nested type, which should already be
-  // complete.
+  // Gets the type info for a nested type, which should already be complete.
   auto GetNestedInfo(SemIR::TypeId nested_type_id) const
       -> SemIR::CompleteTypeInfo;
 
   template <typename InstT>
     requires(InstT::Kind.template IsAnyOf<
-             SemIR::AutoType, SemIR::BoolType, SemIR::BoundMethodType,
-             SemIR::CharLiteralType, SemIR::ErrorInst, SemIR::FacetType,
-             SemIR::FloatLiteralType, SemIR::FloatType, SemIR::FormType,
-             SemIR::IntType, SemIR::IntLiteralType, SemIR::NamespaceType,
-             SemIR::PatternType, SemIR::PointerType,
-             SemIR::RequireSpecificDefinitionType, SemIR::SpecificFunctionType,
-             SemIR::TypeType, SemIR::VtableType, SemIR::WitnessType>())
+             SemIR::AutoType, SemIR::BoundMethodType, SemIR::CharLiteralType,
+             SemIR::ErrorInst, SemIR::FacetType, SemIR::FloatLiteralType,
+             SemIR::FormType, SemIR::IntLiteralType, SemIR::NamespaceType,
+             SemIR::PatternType, SemIR::RequireSpecificDefinitionType,
+             SemIR::SpecificFunctionType, SemIR::TypeType, SemIR::VtableType,
+             SemIR::WitnessType>())
   auto BuildInfoForInst(SemIR::TypeId type_id, InstT /*inst*/) const
       -> SemIR::CompleteTypeInfo {
-    return {.value_repr = MakeCopyValueRepr(type_id)};
+    // These types are empty at runtime but have values to copy at compile time.
+    return {.value_repr = MakeCopyValueRepr(type_id),
+            .object_layout = SemIR::ObjectLayout::Empty()};
   }
 
+  auto BuildInfoForInst(SemIR::TypeId type_id, SemIR::BoolType inst) const
+      -> SemIR::CompleteTypeInfo;
+  auto BuildInfoForInst(SemIR::TypeId type_id, SemIR::PointerType inst) const
+      -> SemIR::CompleteTypeInfo;
+  auto BuildInfoForInst(SemIR::TypeId type_id, SemIR::IntType inst) const
+      -> SemIR::CompleteTypeInfo;
+  auto BuildInfoForInst(SemIR::TypeId type_id, SemIR::FloatType inst) const
+      -> SemIR::CompleteTypeInfo;
+
   auto BuildStructOrTupleValueRepr(size_t num_elements,
                                    SemIR::TypeId elementwise_rep,
                                    bool same_as_object_rep) const
@@ -297,7 +308,7 @@ class TypeCompleter {
     // - For an interface, we could use a witness.
     // - For an associated entity, we could use an index into the witness.
     // - For an unbound element, we could use an index or offset.
-    return {.value_repr = MakeEmptyValueRepr()};
+    return MakeEmptyTypeInfo();
   }
 
   auto BuildInfoForInst(SemIR::TypeId /*type_id*/, SemIR::ConstType inst) const
@@ -330,7 +341,7 @@ class TypeCompleter {
     requires(InstT::Kind.is_symbolic_when_type())
   auto BuildInfoForInst(SemIR::TypeId type_id, InstT /*inst*/) const
       -> SemIR::CompleteTypeInfo {
-    return {.value_repr = MakeDependentValueRepr(type_id)};
+    return MakeDependentTypeInfo(type_id);
   }
 
   // Builds and returns the `CompleteTypeInfo` for the given type. All nested
@@ -501,14 +512,17 @@ auto TypeCompleter::AddNestedIncompleteTypes(SemIR::Inst type_inst) -> bool {
   return true;
 }
 
-auto TypeCompleter::MakeEmptyValueRepr() const -> SemIR::ValueRepr {
-  return {.kind = SemIR::ValueRepr::None,
-          .type_id = GetTupleType(*context_, {})};
+auto TypeCompleter::MakeEmptyTypeInfo() const -> SemIR::CompleteTypeInfo {
+  return {.value_repr = {.kind = SemIR::ValueRepr::None,
+                         .type_id = GetTupleType(*context_, {})},
+          .object_layout = SemIR::ObjectLayout::Empty()};
 }
 
-auto TypeCompleter::MakeDependentValueRepr(SemIR::TypeId type_id) const
-    -> SemIR::ValueRepr {
-  return {.kind = SemIR::ValueRepr::Dependent, .type_id = type_id};
+auto TypeCompleter::MakeDependentTypeInfo(SemIR::TypeId type_id) const
+    -> SemIR::CompleteTypeInfo {
+  return {
+      .value_repr = {.kind = SemIR::ValueRepr::Dependent, .type_id = type_id},
+      .object_layout = SemIR::ObjectLayout()};
 }
 
 auto TypeCompleter::MakeCopyValueRepr(
@@ -565,7 +579,7 @@ auto TypeCompleter::BuildInfoForInst(SemIR::TypeId type_id,
     -> SemIR::CompleteTypeInfo {
   auto fields = context_->struct_type_fields().Get(struct_type.fields_id);
   if (fields.empty()) {
-    return {.value_repr = MakeEmptyValueRepr()};
+    return MakeEmptyTypeInfo();
   }
 
   // Find the value representation for each field, and construct a struct
@@ -574,6 +588,7 @@ auto TypeCompleter::BuildInfoForInst(SemIR::TypeId type_id,
   value_rep_fields.reserve(fields.size());
   bool same_as_object_rep = true;
   SemIR::ClassId abstract_class_id = SemIR::ClassId::None;
+  SemIR::ObjectLayout layout = SemIR::ObjectLayout::Empty();
   for (auto field : fields) {
     auto field_type_id =
         context_->types().GetTypeIdForTypeInstId(field.type_inst_id);
@@ -590,6 +605,8 @@ auto TypeCompleter::BuildInfoForInst(SemIR::TypeId type_id,
         !abstract_class_id.has_value()) {
       abstract_class_id = field_info.abstract_class_id;
     }
+    // Accumulate layout.
+    layout.TryAppendField(field_info.object_layout);
   }
 
   auto value_rep =
@@ -600,6 +617,7 @@ auto TypeCompleter::BuildInfoForInst(SemIR::TypeId type_id,
                 context_->struct_type_fields().AddCanonical(value_rep_fields));
   return {.value_repr = BuildStructOrTupleValueRepr(fields.size(), value_rep,
                                                     same_as_object_rep),
+          .object_layout = layout,
           .abstract_class_id = abstract_class_id};
 }
 
@@ -609,7 +627,7 @@ auto TypeCompleter::BuildInfoForInst(SemIR::TypeId type_id,
   // TODO: Share more code with structs.
   auto elements = context_->inst_blocks().Get(tuple_type.type_elements_id);
   if (elements.empty()) {
-    return {.value_repr = MakeEmptyValueRepr()};
+    return MakeEmptyTypeInfo();
   }
 
   // Find the value representation for each element, and construct a tuple
@@ -618,6 +636,7 @@ auto TypeCompleter::BuildInfoForInst(SemIR::TypeId type_id,
   value_rep_elements.reserve(elements.size());
   bool same_as_object_rep = true;
   SemIR::ClassId abstract_class_id = SemIR::ClassId::None;
+  SemIR::ObjectLayout layout = SemIR::ObjectLayout::Empty();
   for (auto element_type_id : context_->types().GetBlockAsTypeIds(elements)) {
     auto element_info = GetNestedInfo(element_type_id);
     if (!element_info.value_repr.IsCopyOfObjectRepr(context_->sem_ir(),
@@ -631,6 +650,8 @@ auto TypeCompleter::BuildInfoForInst(SemIR::TypeId type_id,
         !abstract_class_id.has_value()) {
       abstract_class_id = element_info.abstract_class_id;
     }
+    // Accumulate layout.
+    layout.TryAppendField(element_info.object_layout);
   }
 
   auto value_rep = same_as_object_rep
@@ -638,17 +659,80 @@ auto TypeCompleter::BuildInfoForInst(SemIR::TypeId type_id,
                        : GetTupleType(*context_, value_rep_elements);
   return {.value_repr = BuildStructOrTupleValueRepr(elements.size(), value_rep,
                                                     same_as_object_rep),
+          .object_layout = layout,
           .abstract_class_id = abstract_class_id};
 }
 
 auto TypeCompleter::BuildInfoForInst(SemIR::TypeId type_id,
-                                     SemIR::ArrayType /*inst*/) const
+                                     SemIR::ArrayType array_type) const
     -> SemIR::CompleteTypeInfo {
   // For arrays, it's convenient to always use a pointer representation,
   // even when the array has zero or one element, in order to support
   // indexing.
+  auto element_type_id =
+      context_->types().GetTypeIdForTypeInstId(array_type.element_type_inst_id);
+  auto element_info = GetNestedInfo(element_type_id);
+
+  SemIR::ObjectLayout layout;
+  if (element_info.object_layout.has_value()) {
+    if (auto bound = context_->sem_ir().GetZExtIntValue(array_type.bound_id)) {
+      layout =
+          SemIR::ObjectLayout::ForArray(element_info.object_layout, *bound);
+    }
+  }
+
   return {.value_repr =
-              MakePointerValueRepr(type_id, SemIR::ValueRepr::ObjectAggregate)};
+              MakePointerValueRepr(type_id, SemIR::ValueRepr::ObjectAggregate),
+          .object_layout = layout};
+}
+
+auto TypeCompleter::BuildInfoForInst(SemIR::TypeId type_id,
+                                     SemIR::BoolType /*inst*/) const
+    -> SemIR::CompleteTypeInfo {
+  // TODO: Decide whether to use a size of `1` here, like `Core.Int(1)`. One
+  // concern is that {.a: bool, .b: bool} would be laid out with the bools at
+  // offsets 0 and 8, which on big-endian systems would imply the MSB stores the
+  // value not the LSB. Consider right-aligning fields on big-endian systems
+  // instead (except when bit-packing, by whatever means we support that).
+  return {.value_repr = MakeCopyValueRepr(type_id),
+          .object_layout = {.size = SemIR::ObjectSize::Bytes(1),
+                            .alignment = SemIR::ObjectSize::Bytes(1)}};
+}
+
+auto TypeCompleter::BuildInfoForInst(SemIR::TypeId type_id,
+                                     SemIR::PointerType /*inst*/) const
+    -> SemIR::CompleteTypeInfo {
+  return {.value_repr = MakeCopyValueRepr(type_id),
+          .object_layout = context_->sem_ir().GetPointerLayout()};
+}
+
+auto TypeCompleter::BuildInfoForInst(SemIR::TypeId type_id,
+                                     SemIR::IntType inst) const
+    -> SemIR::CompleteTypeInfo {
+  SemIR::ObjectLayout layout;
+  if (auto bit_width = context_->sem_ir().GetZExtIntValue(inst.bit_width_id)) {
+    auto size = SemIR::ObjectSize::Bits(*bit_width);
+    // TODO: The upper bound for alignment here should be target-specific.
+    auto align = SemIR::ObjectSize::Bits(
+        std::clamp<int64_t>(llvm::PowerOf2Ceil(*bit_width), 8, 256));
+    layout = {.size = size, .alignment = align};
+  }
+  return {.value_repr = MakeCopyValueRepr(type_id), .object_layout = layout};
+}
+
+auto TypeCompleter::BuildInfoForInst(SemIR::TypeId type_id,
+                                     SemIR::FloatType inst) const
+    -> SemIR::CompleteTypeInfo {
+  SemIR::ObjectLayout layout;
+  if (auto bit_width = context_->sem_ir().GetZExtIntValue(inst.bit_width_id)) {
+    auto size = SemIR::ObjectSize::Bits(*bit_width);
+    // TODO: Pick a suitable alignment here. For some targets, we may want to
+    // use 32-bit alignment for f64 (and f80). For now we round up to a power
+    // of 2.
+    auto align = SemIR::ObjectSize::Bits(llvm::PowerOf2Ceil(*bit_width));
+    layout = {.size = size, .alignment = align};
+  }
+  return {.value_repr = MakeCopyValueRepr(type_id), .object_layout = layout};
 }
 
 auto TypeCompleter::BuildInfoForInst(SemIR::TypeId /*type_id*/,
@@ -660,8 +744,8 @@ auto TypeCompleter::BuildInfoForInst(SemIR::TypeId /*type_id*/,
           ? inst.class_id
           : SemIR::ClassId::None;
 
-  // The value representation of an adapter is the value representation of
-  // its adapted type.
+  // The object and value representation of an adapter are the object and value
+  // representation of its adapted type.
   if (auto adapted_type_id =
           class_info.GetAdaptedType(context_->sem_ir(), inst.specific_id);
       adapted_type_id.has_value()) {
@@ -670,29 +754,35 @@ auto TypeCompleter::BuildInfoForInst(SemIR::TypeId /*type_id*/,
     return info;
   }
   // Otherwise, the value representation for a class is a pointer to the
-  // object representation.
+  // object representation, which was computed when the class was defined.
+  auto object_repr_type_id =
+      class_info.GetObjectRepr(context_->sem_ir(), inst.specific_id);
   // TODO: Support customized value representations for classes.
   // TODO: Pick a better value representation when possible.
-  return {.value_repr = MakePointerValueRepr(
-              class_info.GetObjectRepr(context_->sem_ir(), inst.specific_id),
-              SemIR::ValueRepr::ObjectAggregate),
+  return {.value_repr = MakePointerValueRepr(object_repr_type_id,
+                                             SemIR::ValueRepr::ObjectAggregate),
+          .object_layout = GetNestedInfo(object_repr_type_id).object_layout,
           .abstract_class_id = abstract_class_id};
 }
 
 auto TypeCompleter::BuildInfoForInst(SemIR::TypeId /*type_id*/,
                                      SemIR::ConstType inst) const
     -> SemIR::CompleteTypeInfo {
-  // The value representation of `const T` is the same as that of `T`.
-  // Objects are not modifiable through their value representations.
+  // The object and value representation of `const T` are the same as those of
+  // `T`. Objects are not modifiable through their value representations.
   return GetNestedInfo(context_->types().GetTypeIdForTypeInstId(inst.inner_id));
 }
 
 auto TypeCompleter::BuildInfoForInst(SemIR::TypeId type_id,
-                                     SemIR::CustomLayoutType /*inst*/) const
+                                     SemIR::CustomLayoutType inst) const
     -> SemIR::CompleteTypeInfo {
   // TODO: Should we support other value representations for custom layout
   // types?
-  return {.value_repr = MakePointerValueRepr(type_id)};
+  const auto& layout = context_->custom_layouts().Get(inst.layout_id);
+  return {.value_repr = MakePointerValueRepr(type_id),
+          .object_layout = {
+              .size = layout[SemIR::CustomLayoutId::SizeIndex],
+              .alignment = layout[SemIR::CustomLayoutId::AlignIndex]}};
 }
 
 auto TypeCompleter::BuildInfoForInst(SemIR::TypeId type_id,
@@ -726,11 +816,10 @@ auto TypeCompleter::BuildInfoForInst(SemIR::TypeId /*type_id*/,
   // The value representation of `partial T` is the same as that of `T`.
   // Objects are not modifiable through their value representations. However,
   // `partial T` is never abstract.
-  return {
-      .value_repr =
-          GetNestedInfo(context_->types().GetTypeIdForTypeInstId(inst.inner_id))
-              .value_repr,
-      .abstract_class_id = SemIR::ClassId::None};
+  auto inner_type_id = context_->types().GetTypeIdForTypeInstId(inst.inner_id);
+  auto info = GetNestedInfo(inner_type_id);
+  info.abstract_class_id = SemIR::ClassId::None;
+  return info;
 }
 
 auto TypeCompleter::BuildInfoForInst(
diff --git a/toolchain/driver/testdata/stdin.carbon b/toolchain/driver/testdata/stdin.carbon
index e16a8f07cc80..5bc246b5a150 100644
--- a/toolchain/driver/testdata/stdin.carbon
+++ b/toolchain/driver/testdata/stdin.carbon
@@ -49,12 +49,24 @@
 // CHECK:STDOUT:   types:
 // CHECK:STDOUT:     'type(TypeType)':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(TypeType)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst(FormType))':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(inst(FormType))}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(Error)':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(Error)}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:     'type(inst(NamespaceType))':
 // CHECK:STDOUT:       value_repr:      {kind: copy, type: type(inst(NamespaceType))}
+// CHECK:STDOUT:       object_layout:
+// CHECK:STDOUT:         size:            0
+// CHECK:STDOUT:         alignment:       1
 // CHECK:STDOUT:   facet_types:     {}
 // CHECK:STDOUT:   insts:
 // CHECK:STDOUT:     instF:           {kind: Namespace, arg0: name_scope0, arg1: inst<none>, type: type(inst(NamespaceType))}
diff --git a/toolchain/lower/aggregate.cpp b/toolchain/lower/aggregate.cpp
index 25681b7ffb27..076a653ca351 100644
--- a/toolchain/lower/aggregate.cpp
+++ b/toolchain/lower/aggregate.cpp
@@ -7,6 +7,7 @@
 #include "llvm/ADT/STLExtras.h"
 #include "toolchain/sem_ir/expr_info.h"
 #include "toolchain/sem_ir/inst.h"
+#include "toolchain/sem_ir/type_info.h"
 #include "toolchain/sem_ir/typed_insts.h"
 
 namespace Carbon::Lower {
@@ -28,9 +29,12 @@ static auto GetElementIndex(FunctionContext::TypeInFile type,
     // For custom layout types, we form an array of i8 as the LLVM type, so the
     // offset in the type is the getelementptr index.
     // TODO: This offset might not fit into an `unsigned int`.
-    return type.file->custom_layouts().Get(
+    auto offset = type.file->custom_layouts().Get(
         custom_layout_type
             ->layout_id)[SemIR::CustomLayoutId::FirstFieldIndex + idx.index];
+    CARBON_CHECK(offset == offset.AlignedTo(SemIR::ObjectSize::Bytes(1)),
+                 "Element offset not byte-aligned: {0}", offset);
+    return offset.bytes();
   }
 
   // For now, struct and tuple types map directly into LLVM struct types with
diff --git a/toolchain/lower/constant.cpp b/toolchain/lower/constant.cpp
index cf76a0f0aee7..86830f4367bc 100644
--- a/toolchain/lower/constant.cpp
+++ b/toolchain/lower/constant.cpp
@@ -110,6 +110,34 @@ class ConstantContext {
   SemIR::InstId current_constant_inst_id_ = SemIR::InstId::None;
 };
 
+// Get the element type at a given index from a struct.
+static auto GetElementType(llvm::StructType* struct_type, int index)
+    -> llvm::Type* {
+  return struct_type->getElementType(index);
+}
+
+// Get the element type from an array.
+static auto GetElementType(llvm::ArrayType* array_type, int /*index*/)
+    -> llvm::Type* {
+  return array_type->getElementType();
+}
+
+// Add padding if necessary to convert the given constant to the specified,
+// possibly-padded LLVM type. The type of the constant will either already be
+// `llvm_type`, or will be a tail-padded type `<{llvm_type, [i8 x N]}>`.
+static auto PadToType(llvm::Constant* constant, llvm::Type* llvm_type)
+    -> llvm::Constant* {
+  if (constant->getType() == llvm_type) {
+    return constant;
+  }
+  auto* padded = cast<llvm::StructType>(llvm_type);
+  CARBON_CHECK(padded->getNumElements() == 2 &&
+                   padded->getElementType(0) == constant->getType(),
+               "Unexpected type {0} for constant {1}", *llvm_type, *constant);
+  return llvm::ConstantStruct::get(
+      padded, constant, llvm::PoisonValue::get(padded->getElementType(1)));
+}
+
 // Emits an aggregate constant of LLVM type `Type` whose elements are the
 // contents of `refs_id`.
 template <typename ConstantType, typename Type>
@@ -119,9 +147,10 @@ static auto EmitAggregateConstant(ConstantContext& context,
   auto refs = context.sem_ir().inst_blocks().Get(refs_id);
   llvm::SmallVector<llvm::Constant*> elements;
   elements.reserve(refs.size());
-  for (auto ref : refs) {
+  for (auto [i, ref] : llvm::enumerate(refs)) {
     if (auto* constant = context.GetConstant(ref)) {
-      elements.push_back(constant);
+      auto* elem_type = GetElementType(llvm_type, i);
+      elements.push_back(PadToType(constant, elem_type));
     } else {
       return nullptr;
     }
diff --git a/toolchain/lower/file_context.cpp b/toolchain/lower/file_context.cpp
index 107386dd86a8..8f067344f3c1 100644
--- a/toolchain/lower/file_context.cpp
+++ b/toolchain/lower/file_context.cpp
@@ -38,6 +38,7 @@
 #include "toolchain/sem_ir/mangler.h"
 #include "toolchain/sem_ir/pattern.h"
 #include "toolchain/sem_ir/stringify.h"
+#include "toolchain/sem_ir/type_info.h"
 #include "toolchain/sem_ir/typed_insts.h"
 
 namespace Carbon::Lower {
@@ -1191,6 +1192,22 @@ auto FileContext::BuildDISubprogram(const SemIR::Function& function,
   return subprogram;
 }
 
+// Given an LLVM type, build a corresponding type with `padding_bytes` bytes of
+// explicit tail padding.
+static auto BuildTailPaddedType(llvm::Type* subtype, int64_t padding_bytes)
+    -> llvm::Type* {
+  if (padding_bytes == 0) {
+    return subtype;
+  }
+  // Build the type `<{subtype, [i8 x padding_bytes]}>`.
+  llvm::Type* type_with_padding[2] = {
+      subtype,
+      llvm::ArrayType::get(llvm::Type::getInt8Ty(subtype->getContext()),
+                           padding_bytes)};
+  return llvm::StructType::get(subtype->getContext(), type_with_padding,
+                               /*isPacked=*/true);
+}
+
 // BuildTypeForInst is used to construct types for FileContext::BuildType below.
 // Implementations return the LLVM type for the instruction. This first overload
 // is the fallback handler for non-type instructions.
@@ -1211,10 +1228,25 @@ static auto BuildTypeForInst(FileContext& context, InstT /*inst*/)
 
 static auto BuildTypeForInst(FileContext& context, SemIR::ArrayType inst)
     -> FileContext::LoweredTypes {
+  auto elem_type_id = context.sem_ir().types().GetTypeIdForTypeInstId(
+      inst.element_type_inst_id);
+  auto stride = context.sem_ir()
+                    .types()
+                    .GetCompleteTypeInfo(elem_type_id)
+                    .object_layout.ArrayStride();
+
+  auto* elem_type = context.GetType(elem_type_id);
+  auto elem_size = SemIR::ObjectSize::Bytes(
+      context.llvm_module().getDataLayout().getTypeAllocSize(elem_type));
+
+  if (elem_size != stride) {
+    CARBON_CHECK(elem_size < stride, "Array element type too large");
+    elem_type = BuildTailPaddedType(context.GetType(elem_type_id),
+                                    stride.bytes() - elem_size.bytes());
+  }
+
   return {llvm::ArrayType::get(
-              context.GetType(context.sem_ir().types().GetTypeIdForTypeInstId(
-                  inst.element_type_inst_id)),
-              *context.sem_ir().GetArrayBoundValue(inst.bound_id)),
+              elem_type, *context.sem_ir().GetZExtIntValue(inst.bound_id)),
           nullptr};
 }
 
@@ -1246,9 +1278,10 @@ static auto BuildTypeForInst(FileContext& context, InstT inst)
 static auto BuildTypeForInst(FileContext& context, SemIR::CustomLayoutType inst)
     -> FileContext::LoweredTypes {
   auto layout = context.sem_ir().custom_layouts().Get(inst.layout_id);
-  return {llvm::ArrayType::get(llvm::Type::getInt8Ty(context.llvm_context()),
-                               layout[SemIR::CustomLayoutId::SizeIndex]),
-          nullptr};
+  return {
+      llvm::ArrayType::get(llvm::Type::getInt8Ty(context.llvm_context()),
+                           layout[SemIR::CustomLayoutId::SizeIndex].bytes()),
+      nullptr};
 }
 
 static auto BuildTypeForInst(FileContext& context,
@@ -1296,16 +1329,99 @@ static auto BuildTypeForInst(FileContext& /*context*/,
   CARBON_FATAL("Unexpected pattern type in lowering");
 }
 
+// Builds an LLVM packed struct type whose layout matches the Carbon layout for
+// an aggregate with the given field types and field layouts.
+static auto BuildPackedStructType(FileContext& context,
+                                  llvm::MutableArrayRef<llvm::Type*> subtypes,
+                                  llvm::ArrayRef<SemIR::ObjectLayout> layouts)
+    -> llvm::StructType* {
+  const auto& data_layout = context.llvm_module().getDataLayout();
+  auto struct_layout = SemIR::ObjectLayout::Empty();
+  auto size_so_far = SemIR::ObjectSize::Zero();
+
+  llvm::Type** previous_type = nullptr;
+  for (auto [type, layout] : llvm::zip_equal(subtypes, layouts)) {
+    auto offset = struct_layout.FieldOffset(layout);
+    // If this field has padding before it, represent that padding explicitly as
+    // part of the previous field. This allows us to always use GEP indexes that
+    // match the field indexes.
+    if (offset != size_so_far) {
+      CARBON_CHECK(previous_type, "Padding before first field?");
+      CARBON_CHECK(offset > size_so_far, "Extraneous padding after field {0}",
+                   **previous_type);
+      int64_t padding_bytes = offset.bytes() - struct_layout.size.bytes();
+      *previous_type = BuildTailPaddedType(*previous_type, padding_bytes);
+      size_so_far += SemIR::ObjectSize::Bytes(padding_bytes);
+      CARBON_CHECK(offset == size_so_far, "Field at non-byte offset");
+    }
+
+    size_so_far += SemIR::ObjectSize::Bytes(data_layout.getTypeAllocSize(type));
+    struct_layout.AppendField(layout);
+    previous_type = &type;
+  }
+  return llvm::StructType::get(context.llvm_context(), subtypes,
+                               /*isPacked=*/true);
+}
+
+// Returns whether the given LLVM layout matches the expected Carbon layout for
+// an aggregate with the given field layouts.
+static auto StructLayoutMatches(llvm::ArrayRef<SemIR::ObjectLayout> layouts,
+                                const llvm::StructLayout& llvm_layout) -> bool {
+  auto struct_layout = SemIR::ObjectLayout::Empty();
+
+  // Check each field is at the right offset.
+  for (auto [i, layout] : llvm::enumerate(layouts)) {
+    if (static_cast<int64_t>(llvm_layout.getElementOffsetInBits(i)) !=
+        struct_layout.FieldOffset(layout).bits()) {
+      return false;
+    }
+    struct_layout.AppendField(layout);
+  }
+
+  // Treat the LLVM layout as being acceptable if it's the right byte size and
+  // does not require more alignment than the Carbon type. We could ignore the
+  // alignment, but an overaligned LLVM type will prevent the type from being
+  // used in non-packed structs in more situations.
+  return static_cast<int64_t>(llvm_layout.getSizeInBytes()) ==
+             struct_layout.size.bytes() &&
+         llvm_layout.getAlignment() <=
+             llvm::Align(struct_layout.alignment.bytes());
+}
+
+// Builds an LLVM struct type whose layout matches the Carbon layout for an
+// aggregate with the given field types and field layouts.
+static auto BuildStructType(FileContext& context,
+                            llvm::MutableArrayRef<llvm::Type*> subtypes,
+                            llvm::ArrayRef<SemIR::ObjectLayout> layouts)
+    -> FileContext::LoweredTypes {
+  // Opportunistically try building an llvm StructType from the subtypes. If it
+  // has the right layout, we're done. We prefer to use a non-packed struct type
+  // where possible to produce a smaller LLVM IR representation for the type and
+  // for constant values of the type, and to improve the readability of the IR.
+  auto* struct_type = llvm::StructType::get(context.llvm_context(), subtypes);
+  if (!StructLayoutMatches(
+          layouts, *context.llvm_module().getDataLayout().getStructLayout(
+                       struct_type))) {
+    struct_type = BuildPackedStructType(context, subtypes, layouts);
+  }
+  return {struct_type, nullptr};
+}
+
 static auto BuildTypeForInst(FileContext& context, SemIR::StructType inst)
     -> FileContext::LoweredTypes {
   auto fields = context.sem_ir().struct_type_fields().Get(inst.fields_id);
   llvm::SmallVector<llvm::Type*> subtypes;
+  llvm::SmallVector<SemIR::ObjectLayout> layouts;
   subtypes.reserve(fields.size());
+  layouts.reserve(fields.size());
   for (auto field : fields) {
-    subtypes.push_back(context.GetType(
-        context.sem_ir().types().GetTypeIdForTypeInstId(field.type_inst_id)));
+    auto type_id =
+        context.sem_ir().types().GetTypeIdForTypeInstId(field.type_inst_id);
+    subtypes.push_back(context.GetType(type_id));
+    layouts.push_back(
+        context.sem_ir().types().GetCompleteTypeInfo(type_id).object_layout);
   }
-  return {llvm::StructType::get(context.llvm_context(), subtypes), nullptr};
+  return BuildStructType(context, subtypes, layouts);
 }
 
 static auto BuildTypeForInst(FileContext& context, SemIR::TupleType inst)
@@ -1316,11 +1432,15 @@ static auto BuildTypeForInst(FileContext& context, SemIR::TupleType inst)
   // type, so that may require significant special casing.
   auto elements = context.sem_ir().inst_blocks().Get(inst.type_elements_id);
   llvm::SmallVector<llvm::Type*> subtypes;
+  llvm::SmallVector<SemIR::ObjectLayout> layouts;
   subtypes.reserve(elements.size());
+  layouts.reserve(elements.size());
   for (auto type_id : context.sem_ir().types().GetBlockAsTypeIds(elements)) {
     subtypes.push_back(context.GetType(type_id));
+    layouts.push_back(
+        context.sem_ir().types().GetCompleteTypeInfo(type_id).object_layout);
   }
-  return {llvm::StructType::get(context.llvm_context(), subtypes), nullptr};
+  return BuildStructType(context, subtypes, layouts);
 }
 
 static auto BuildTypeForInst(FileContext& context, SemIR::TypeType /*inst*/)
@@ -1338,12 +1458,6 @@ static auto BuildTypeForInst(FileContext& context, SemIR::VtableType /*inst*/)
   return {llvm::Type::getVoidTy(context.llvm_context()), nullptr};
 }
 
-static auto BuildTypeForInst(FileContext& context,
-                             SemIR::SpecificFunctionType /*inst*/)
-    -> FileContext::LoweredTypes {
-  return {llvm::PointerType::get(context.llvm_context(), 0), nullptr};
-}
-
 template <typename InstT>
   requires(InstT::Kind.template IsAnyOf<
            SemIR::AssociatedEntityType, SemIR::AutoType, SemIR::BoundMethodType,
@@ -1353,8 +1467,8 @@ template <typename InstT>
            SemIR::FunctionTypeWithSelfType, SemIR::GenericClassType,
            SemIR::GenericInterfaceType, SemIR::GenericNamedConstraintType,
            SemIR::InstType, SemIR::IntLiteralType, SemIR::NamespaceType,
-           SemIR::RequireSpecificDefinitionType, SemIR::UnboundElementType,
-           SemIR::WhereExpr, SemIR::WitnessType>())
+           SemIR::RequireSpecificDefinitionType, SemIR::SpecificFunctionType,
+           SemIR::UnboundElementType, SemIR::WhereExpr, SemIR::WitnessType>())
 static auto BuildTypeForInst(FileContext& context, InstT /*inst*/)
     -> FileContext::LoweredTypes {
   // Return an empty struct as a placeholder.
@@ -1366,13 +1480,42 @@ static auto BuildTypeForInst(FileContext& context, InstT /*inst*/)
 auto FileContext::BuildType(SemIR::InstId inst_id) -> LoweredTypes {
   // Use overload resolution to select the implementation, producing compile
   // errors when BuildTypeForInst isn't defined for a given instruction.
+  LoweredTypes result;
   CARBON_KIND_SWITCH(sem_ir_->insts().Get(inst_id)) {
-#define CARBON_SEM_IR_INST_KIND(Name)     \
-  case CARBON_KIND(SemIR::Name inst): {   \
-    return BuildTypeForInst(*this, inst); \
+#define CARBON_SEM_IR_INST_KIND(Name)       \
+  case CARBON_KIND(SemIR::Name inst): {     \
+    result = BuildTypeForInst(*this, inst); \
+    break;                                  \
   }
 #include "toolchain/sem_ir/inst_kind.def"
   }
+
+  // In debug builds, check that the type we built has the expected size.
+  CARBON_DCHECK([&] {
+    if (!result.llvm_ir_type) {
+      return true;
+    }
+    const auto& layout = llvm_module().getDataLayout();
+    auto expected_layout =
+        sem_ir()
+            .types()
+            .GetCompleteTypeInfo(
+                sem_ir().types().GetTypeIdForTypeInstId(inst_id))
+            .object_layout;
+    CARBON_CHECK(expected_layout.has_value());
+    auto size =
+        SemIR::ObjectSize::Bits(layout.getTypeSizeInBits(result.llvm_ir_type));
+    // Round up to byte granularity for this check, since LLVM doesn't support
+    // non-byte-sized packed structs.
+    CARBON_CHECK(
+        size.bytes() == expected_layout.size.bytes(),
+        "Lowered type {0} for {1} has unexpected size {2}, expected {3}",
+        *result.llvm_ir_type, sem_ir().insts().Get(inst_id), size,
+        expected_layout.size);
+    return true;
+  }());
+
+  return result;
 }
 
 auto FileContext::BuildGlobalVariableDecl(SemIR::VarStorage var_storage)
diff --git a/toolchain/lower/function_context.cpp b/toolchain/lower/function_context.cpp
index 5469b914b027..3cb023fd3f4d 100644
--- a/toolchain/lower/function_context.cpp
+++ b/toolchain/lower/function_context.cpp
@@ -276,6 +276,7 @@ auto FunctionContext::InitializeStorage(TypeInFile type, SemIR::InstId dest_id,
       if (sem_ir().constant_values().Get(source_id).is_constant()) {
         // When initializing from a constant, emission of the source doesn't
         // initialize the destination. Copy the constant value instead.
+        // TODO: If the type is small, emit a store rather than a memcpy.
         CopyValue(type, source_id, dest_id);
       }
       break;
diff --git a/toolchain/lower/handle_call.cpp b/toolchain/lower/handle_call.cpp
index 3041f6b6bc26..a6b6810109d2 100644
--- a/toolchain/lower/handle_call.cpp
+++ b/toolchain/lower/handle_call.cpp
@@ -269,7 +269,7 @@ static auto StoreArrayAsStdInitializerList(FunctionContext& context,
       context.GetTypeIdOfInst(array_inst_id);
   auto array_type = array_type_file->types().GetAs<SemIR::ArrayType>(
       array_type_file->types().GetObjectRepr(array_type_id));
-  auto array_bound = array_type_file->GetArrayBoundValue(array_type.bound_id);
+  auto array_bound = array_type_file->GetZExtIntValue(array_type.bound_id);
   CARBON_CHECK(array_bound, "Array type with non-constant bound");
 
   // Store the array pointer in the first element of the initializer list.
diff --git a/toolchain/lower/testdata/array/iterate.carbon b/toolchain/lower/testdata/array/iterate.carbon
index 5de42bb033dd..257ad89a5c2b 100644
--- a/toolchain/lower/testdata/array/iterate.carbon
+++ b/toolchain/lower/testdata/array/iterate.carbon
@@ -32,7 +32,7 @@ fn F() {
 // CHECK:STDOUT: entry:
 // CHECK:STDOUT:   %.loc16_43.3.temp = alloca [6 x i32], align 4, !dbg !7
 // CHECK:STDOUT:   %var = alloca i32, align 4, !dbg !8
-// CHECK:STDOUT:   %.loc17_19.1.temp = alloca { i32, i1 }, align 8, !dbg !8
+// CHECK:STDOUT:   %.loc17_19.1.temp = alloca <{ i32, i1 }>, align 8, !dbg !8
 // CHECK:STDOUT:   call void @llvm.lifetime.start.p0(ptr %.loc16_43.3.temp), !dbg !7
 // CHECK:STDOUT:   %.loc16_43.4.array.index = getelementptr inbounds [6 x i32], ptr %.loc16_43.3.temp, i32 0, i64 0, !dbg !7
 // CHECK:STDOUT:   %.loc16_43.7.array.index = getelementptr inbounds [6 x i32], ptr %.loc16_43.3.temp, i32 0, i64 1, !dbg !7
@@ -108,7 +108,7 @@ fn F() {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr void @"_CNext.7711e6f0e1563534:Iterate.Core.355bb079bb00aa16"(ptr sret({ i32, i1 }) %return, ptr %self, ptr %cursor) #0 !dbg !49 {
+// CHECK:STDOUT: define linkonce_odr void @"_CNext.7711e6f0e1563534:Iterate.Core.355bb079bb00aa16"(ptr sret(<{ i32, i1 }>) %return, ptr %self, ptr %cursor) #0 !dbg !49 {
 // CHECK:STDOUT:   %1 = load i32, ptr %cursor, align 4, !dbg !55
 // CHECK:STDOUT:   %2 = icmp slt i32 %1, 6, !dbg !55
 // CHECK:STDOUT:   br i1 %2, label %3, label %7, !dbg !56
@@ -146,20 +146,20 @@ fn F() {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr void @_CSome.Optional.Core.b5e6acce74484d77(ptr sret({ i32, i1 }) %return, i32 %value) #0 !dbg !83 {
+// CHECK:STDOUT: define linkonce_odr void @_CSome.Optional.Core.b5e6acce74484d77(ptr sret(<{ i32, i1 }>) %return, i32 %value) #0 !dbg !83 {
 // CHECK:STDOUT:   call void @"_CSome.3e8267224c5dc9c2:OptionalStorage.Core.bfb441135f07cbe1"(ptr %return, i32 %value), !dbg !88
 // CHECK:STDOUT:   ret void, !dbg !89
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr void @_CNone.Optional.Core.b5e6acce74484d77(ptr sret({ i32, i1 }) %return) #0 !dbg !90 {
+// CHECK:STDOUT: define linkonce_odr void @_CNone.Optional.Core.b5e6acce74484d77(ptr sret(<{ i32, i1 }>) %return) #0 !dbg !90 {
 // CHECK:STDOUT:   call void @"_CNone.3e8267224c5dc9c2:OptionalStorage.Core.bfb441135f07cbe1"(ptr %return), !dbg !93
 // CHECK:STDOUT:   ret void, !dbg !94
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
 // CHECK:STDOUT: define linkonce_odr i1 @"_CHas.3e8267224c5dc9c2:OptionalStorage.Core.bfb441135f07cbe1"(ptr %value) #0 !dbg !95 {
-// CHECK:STDOUT:   %has_value = getelementptr inbounds nuw { i32, i1 }, ptr %value, i32 0, i32 1, !dbg !98
+// CHECK:STDOUT:   %has_value = getelementptr inbounds nuw <{ i32, i1 }>, ptr %value, i32 0, i32 1, !dbg !98
 // CHECK:STDOUT:   %1 = load i8, ptr %has_value, align 1, !dbg !98
 // CHECK:STDOUT:   %2 = trunc i8 %1 to i1, !dbg !98
 // CHECK:STDOUT:   ret i1 %2, !dbg !99
@@ -167,7 +167,7 @@ fn F() {
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
 // CHECK:STDOUT: define linkonce_odr i32 @"_CGet.3e8267224c5dc9c2:OptionalStorage.Core.bfb441135f07cbe1"(ptr %value) #0 !dbg !100 {
-// CHECK:STDOUT:   %value1 = getelementptr inbounds nuw { i32, i1 }, ptr %value, i32 0, i32 0, !dbg !103
+// CHECK:STDOUT:   %value1 = getelementptr inbounds nuw <{ i32, i1 }>, ptr %value, i32 0, i32 0, !dbg !103
 // CHECK:STDOUT:   %1 = load i32, ptr %value1, align 4, !dbg !103
 // CHECK:STDOUT:   ret i32 %1, !dbg !104
 // CHECK:STDOUT: }
@@ -182,17 +182,17 @@ fn F() {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr void @"_CSome.3e8267224c5dc9c2:OptionalStorage.Core.bfb441135f07cbe1"(ptr sret({ i32, i1 }) %return, i32 %self) #0 !dbg !113 {
-// CHECK:STDOUT:   %value = getelementptr inbounds nuw { i32, i1 }, ptr %return, i32 0, i32 0, !dbg !116
+// CHECK:STDOUT: define linkonce_odr void @"_CSome.3e8267224c5dc9c2:OptionalStorage.Core.bfb441135f07cbe1"(ptr sret(<{ i32, i1 }>) %return, i32 %self) #0 !dbg !113 {
+// CHECK:STDOUT:   %value = getelementptr inbounds nuw <{ i32, i1 }>, ptr %return, i32 0, i32 0, !dbg !116
 // CHECK:STDOUT:   store i32 %self, ptr %value, align 4, !dbg !116
-// CHECK:STDOUT:   %has_value = getelementptr inbounds nuw { i32, i1 }, ptr %return, i32 0, i32 1, !dbg !117
+// CHECK:STDOUT:   %has_value = getelementptr inbounds nuw <{ i32, i1 }>, ptr %return, i32 0, i32 1, !dbg !117
 // CHECK:STDOUT:   store i8 1, ptr %has_value, align 1, !dbg !117
 // CHECK:STDOUT:   ret void, !dbg !118
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr void @"_CNone.3e8267224c5dc9c2:OptionalStorage.Core.bfb441135f07cbe1"(ptr sret({ i32, i1 }) %return) #0 !dbg !119 {
-// CHECK:STDOUT:   %has_value = getelementptr inbounds nuw { i32, i1 }, ptr %return, i32 0, i32 1, !dbg !120
+// CHECK:STDOUT: define linkonce_odr void @"_CNone.3e8267224c5dc9c2:OptionalStorage.Core.bfb441135f07cbe1"(ptr sret(<{ i32, i1 }>) %return) #0 !dbg !119 {
+// CHECK:STDOUT:   %has_value = getelementptr inbounds nuw <{ i32, i1 }>, ptr %return, i32 0, i32 1, !dbg !120
 // CHECK:STDOUT:   store i8 0, ptr %has_value, align 1, !dbg !120
 // CHECK:STDOUT:   ret void, !dbg !121
 // CHECK:STDOUT: }
diff --git a/toolchain/lower/testdata/array/layout.carbon b/toolchain/lower/testdata/array/layout.carbon
new file mode 100644
index 000000000000..9d385f8ce732
--- /dev/null
+++ b/toolchain/lower/testdata/array/layout.carbon
@@ -0,0 +1,147 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// INCLUDE-FILE: toolchain/testing/testdata/min_prelude/int.carbon
+//
+// AUTOUPDATE
+// TIP: To test this file alone, run:
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/lower/testdata/array/layout.carbon
+// TIP: To dump output, run:
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/array/layout.carbon
+
+// --- element_tail_padding.carbon
+library "[[@TEST_NAME]]";
+
+fn Check(p: i32*);
+
+fn Test() {
+  // We insert tail padding after each element (including the last) to keep the
+  // array elements properly aligned and to ensure that a past-the-end address
+  // points within the overall object.
+  var v: array({.a: ()*, .b: i32}, 3);
+  Check(&v[0].b);
+  Check(&v[1].b);
+  Check(&v[2].b);
+}
+
+// --- constant_with_padding.carbon
+library "[[@TEST_NAME]]";
+
+var c: array(Core.Int(257), 5) = (1, 2, 3, 4, 5);
+
+// CHECK:STDOUT: ; ModuleID = 'element_tail_padding.carbon'
+// CHECK:STDOUT: source_filename = "element_tail_padding.carbon"
+// CHECK:STDOUT:
+// CHECK:STDOUT: declare void @_CCheck.Main(ptr)
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nounwind
+// CHECK:STDOUT: define void @_CTest.Main() #0 !dbg !4 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %v.var = alloca [3 x <{ <{ ptr, i32 }>, [4 x i8] }>], align 8, !dbg !7
+// CHECK:STDOUT:   call void @llvm.lifetime.start.p0(ptr %v.var), !dbg !7
+// CHECK:STDOUT:   %.loc10_13.array.index = getelementptr inbounds [3 x <{ <{ ptr, i32 }>, [4 x i8] }>], ptr %v.var, i32 0, i32 0, !dbg !8
+// CHECK:STDOUT:   %.loc10_14.b = getelementptr inbounds nuw <{ ptr, i32 }>, ptr %.loc10_13.array.index, i32 0, i32 1, !dbg !8
+// CHECK:STDOUT:   call void @_CCheck.Main(ptr %.loc10_14.b), !dbg !9
+// CHECK:STDOUT:   %.loc11_13.array.index = getelementptr inbounds [3 x <{ <{ ptr, i32 }>, [4 x i8] }>], ptr %v.var, i32 0, i32 1, !dbg !10
+// CHECK:STDOUT:   %.loc11_14.b = getelementptr inbounds nuw <{ ptr, i32 }>, ptr %.loc11_13.array.index, i32 0, i32 1, !dbg !10
+// CHECK:STDOUT:   call void @_CCheck.Main(ptr %.loc11_14.b), !dbg !11
+// CHECK:STDOUT:   %.loc12_13.array.index = getelementptr inbounds [3 x <{ <{ ptr, i32 }>, [4 x i8] }>], ptr %v.var, i32 0, i32 2, !dbg !12
+// CHECK:STDOUT:   %.loc12_14.b = getelementptr inbounds nuw <{ ptr, i32 }>, ptr %.loc12_13.array.index, i32 0, i32 1, !dbg !12
+// CHECK:STDOUT:   call void @_CCheck.Main(ptr %.loc12_14.b), !dbg !13
+// CHECK:STDOUT:   call void @"_COp.876098026a9fba08:core.Destroy.Core"(ptr %v.var), !dbg !7
+// CHECK:STDOUT:   ret void, !dbg !14
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nounwind
+// CHECK:STDOUT: define weak_odr void @"_COp.7e389eab4a7e5487:core.Destroy.Core"(ptr %self) #0 !dbg !15 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   ret void, !dbg !21
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nounwind
+// CHECK:STDOUT: define weak_odr void @"_COp.5e9a928496027250:core.Destroy.Core"(ptr %self) #0 !dbg !22 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   ret void, !dbg !28
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nounwind
+// CHECK:STDOUT: define weak_odr void @"_COp.876098026a9fba08:core.Destroy.Core"(ptr %self) #0 !dbg !29 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   ret void, !dbg !32
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nocallback nofree nosync nounwind willreturn memory(argmem: readwrite)
+// CHECK:STDOUT: declare void @llvm.lifetime.start.p0(ptr captures(none)) #1
+// CHECK:STDOUT:
+// CHECK:STDOUT: attributes #0 = { nounwind }
+// CHECK:STDOUT: attributes #1 = { nocallback nofree nosync nounwind willreturn memory(argmem: readwrite) }
+// CHECK:STDOUT:
+// CHECK:STDOUT: !llvm.module.flags = !{!0, !1}
+// CHECK:STDOUT: !llvm.dbg.cu = !{!2}
+// CHECK:STDOUT:
+// CHECK:STDOUT: !0 = !{i32 7, !"Dwarf Version", i32 5}
+// CHECK:STDOUT: !1 = !{i32 2, !"Debug Info Version", i32 3}
+// CHECK:STDOUT: !2 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !3, producer: "carbon", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug)
+// CHECK:STDOUT: !3 = !DIFile(filename: "element_tail_padding.carbon", directory: "")
+// CHECK:STDOUT: !4 = distinct !DISubprogram(name: "Test", linkageName: "_CTest.Main", scope: null, file: !3, line: 5, type: !5, spFlags: DISPFlagDefinition, unit: !2)
+// CHECK:STDOUT: !5 = !DISubroutineType(types: !6)
+// CHECK:STDOUT: !6 = !{null}
+// CHECK:STDOUT: !7 = !DILocation(line: 9, column: 3, scope: !4)
+// CHECK:STDOUT: !8 = !DILocation(line: 10, column: 10, scope: !4)
+// CHECK:STDOUT: !9 = !DILocation(line: 10, column: 3, scope: !4)
+// CHECK:STDOUT: !10 = !DILocation(line: 11, column: 10, scope: !4)
+// CHECK:STDOUT: !11 = !DILocation(line: 11, column: 3, scope: !4)
+// CHECK:STDOUT: !12 = !DILocation(line: 12, column: 10, scope: !4)
+// CHECK:STDOUT: !13 = !DILocation(line: 12, column: 3, scope: !4)
+// CHECK:STDOUT: !14 = !DILocation(line: 5, column: 1, scope: !4)
+// CHECK:STDOUT: !15 = distinct !DISubprogram(name: "Op", linkageName: "_COp.7e389eab4a7e5487:core.Destroy.Core", scope: null, file: !3, line: 9, type: !16, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !19)
+// CHECK:STDOUT: !16 = !DISubroutineType(types: !17)
+// CHECK:STDOUT: !17 = !{null, !18}
+// CHECK:STDOUT: !18 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+// CHECK:STDOUT: !19 = !{!20}
+// CHECK:STDOUT: !20 = !DILocalVariable(arg: 1, scope: !15, type: !18)
+// CHECK:STDOUT: !21 = !DILocation(line: 9, column: 3, scope: !15)
+// CHECK:STDOUT: !22 = distinct !DISubprogram(name: "Op", linkageName: "_COp.5e9a928496027250:core.Destroy.Core", scope: null, file: !3, line: 9, type: !23, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !26)
+// CHECK:STDOUT: !23 = !DISubroutineType(types: !24)
+// CHECK:STDOUT: !24 = !{null, !25}
+// CHECK:STDOUT: !25 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: null, size: 64)
+// CHECK:STDOUT: !26 = !{!27}
+// CHECK:STDOUT: !27 = !DILocalVariable(arg: 1, scope: !22, type: !25)
+// CHECK:STDOUT: !28 = !DILocation(line: 9, column: 3, scope: !22)
+// CHECK:STDOUT: !29 = distinct !DISubprogram(name: "Op", linkageName: "_COp.876098026a9fba08:core.Destroy.Core", scope: null, file: !3, line: 9, type: !23, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !30)
+// CHECK:STDOUT: !30 = !{!31}
+// CHECK:STDOUT: !31 = !DILocalVariable(arg: 1, scope: !29, type: !25)
+// CHECK:STDOUT: !32 = !DILocation(line: 9, column: 3, scope: !29)
+// CHECK:STDOUT: ; ModuleID = 'constant_with_padding.carbon'
+// CHECK:STDOUT: source_filename = "constant_with_padding.carbon"
+// CHECK:STDOUT:
+// CHECK:STDOUT: @_Cc.Main = global [5 x <{ i257, [28 x i8] }>] zeroinitializer
+// CHECK:STDOUT: @array.loc3_1 = internal constant [5 x <{ i257, [28 x i8] }>] [<{ i257, [28 x i8] }> <{ i257 1, [28 x i8] poison }>, <{ i257, [28 x i8] }> <{ i257 2, [28 x i8] poison }>, <{ i257, [28 x i8] }> <{ i257 3, [28 x i8] poison }>, <{ i257, [28 x i8] }> <{ i257 4, [28 x i8] poison }>, <{ i257, [28 x i8] }> <{ i257 5, [28 x i8] poison }>]
+// CHECK:STDOUT: @llvm.global_ctors = appending global [1 x { i32, ptr, ptr }] [{ i32, ptr, ptr } { i32 0, ptr @_C__global_init.Main, ptr null }]
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nounwind
+// CHECK:STDOUT: define internal void @_C__global_init.Main() #0 !dbg !4 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   call void @llvm.memcpy.p0.p0.i64(ptr align 1 @_Cc.Main, ptr align 1 @array.loc3_1, i64 320, i1 false), !dbg !7
+// CHECK:STDOUT:   ret void, !dbg !8
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nocallback nofree nounwind willreturn memory(argmem: readwrite)
+// CHECK:STDOUT: declare void @llvm.memcpy.p0.p0.i64(ptr noalias writeonly captures(none), ptr noalias readonly captures(none), i64, i1 immarg) #1
+// CHECK:STDOUT:
+// CHECK:STDOUT: attributes #0 = { nounwind }
+// CHECK:STDOUT: attributes #1 = { nocallback nofree nounwind willreturn memory(argmem: readwrite) }
+// CHECK:STDOUT:
+// CHECK:STDOUT: !llvm.module.flags = !{!0, !1}
+// CHECK:STDOUT: !llvm.dbg.cu = !{!2}
+// CHECK:STDOUT:
+// CHECK:STDOUT: !0 = !{i32 7, !"Dwarf Version", i32 5}
+// CHECK:STDOUT: !1 = !{i32 2, !"Debug Info Version", i32 3}
+// CHECK:STDOUT: !2 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !3, producer: "carbon", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug)
+// CHECK:STDOUT: !3 = !DIFile(filename: "constant_with_padding.carbon", directory: "")
+// CHECK:STDOUT: !4 = distinct !DISubprogram(name: "__global_init", linkageName: "_C__global_init.Main", scope: null, file: !3, type: !5, spFlags: DISPFlagDefinition, unit: !2)
+// CHECK:STDOUT: !5 = !DISubroutineType(types: !6)
+// CHECK:STDOUT: !6 = !{null}
+// CHECK:STDOUT: !7 = !DILocation(line: 3, column: 1, scope: !4)
+// CHECK:STDOUT: !8 = !DILocation(line: 0, scope: !4)
diff --git a/toolchain/lower/testdata/class/field.carbon b/toolchain/lower/testdata/class/field.carbon
index 423334e852ee..8c0136d64dfd 100644
--- a/toolchain/lower/testdata/class/field.carbon
+++ b/toolchain/lower/testdata/class/field.carbon
@@ -250,12 +250,12 @@ fn Run() {
 // CHECK:STDOUT: define void @main() #0 !dbg !4 {
 // CHECK:STDOUT: entry:
 // CHECK:STDOUT:   %o.var = alloca { i32 }, align 8, !dbg !7
-// CHECK:STDOUT:   %_.var = alloca { ptr, { i32 } }, align 8, !dbg !8
+// CHECK:STDOUT:   %_.var = alloca <{ ptr, { i32 } }>, align 8, !dbg !8
 // CHECK:STDOUT:   call void @llvm.lifetime.start.p0(ptr %o.var), !dbg !7
 // CHECK:STDOUT:   call void @llvm.lifetime.start.p0(ptr %_.var), !dbg !8
-// CHECK:STDOUT:   %.loc17_40.2.a = getelementptr inbounds nuw { ptr, { i32 } }, ptr %_.var, i32 0, i32 0, !dbg !9
+// CHECK:STDOUT:   %.loc17_40.2.a = getelementptr inbounds nuw <{ ptr, { i32 } }>, ptr %_.var, i32 0, i32 0, !dbg !9
 // CHECK:STDOUT:   store ptr %o.var, ptr %.loc17_40.2.a, align 8, !dbg !9
-// CHECK:STDOUT:   %.loc17_40.4.b = getelementptr inbounds nuw { ptr, { i32 } }, ptr %_.var, i32 0, i32 1, !dbg !9
+// CHECK:STDOUT:   %.loc17_40.4.b = getelementptr inbounds nuw <{ ptr, { i32 } }>, ptr %_.var, i32 0, i32 1, !dbg !9
 // CHECK:STDOUT:   %.loc17_39.3.v = getelementptr inbounds nuw { i32 }, ptr %.loc17_40.4.b, i32 0, i32 0, !dbg !10
 // CHECK:STDOUT:   call void @llvm.memcpy.p0.p0.i64(ptr align 4 %.loc17_40.4.b, ptr align 4 @Other.val.loc17_40.5, i64 4, i1 false), !dbg !9
 // CHECK:STDOUT:   call void @"_COp.6354d5454c7bf77d:core.Destroy.Core"(ptr %_.var), !dbg !8
diff --git a/toolchain/lower/testdata/class/virtual.carbon b/toolchain/lower/testdata/class/virtual.carbon
index 95541235d16c..01d4cc720951 100644
--- a/toolchain/lower/testdata/class/virtual.carbon
+++ b/toolchain/lower/testdata/class/virtual.carbon
@@ -474,7 +474,7 @@ fn Make() {
 // CHECK:STDOUT: source_filename = "member_init.carbon"
 // CHECK:STDOUT:
 // CHECK:STDOUT: @"_CBase.MemberInit.$vtable" = unnamed_addr constant [1 x i32] [i32 trunc (i64 sub (i64 ptrtoint (ptr @_CFn.Base.MemberInit to i64), i64 ptrtoint (ptr @"_CBase.MemberInit.$vtable" to i64)) to i32)]
-// CHECK:STDOUT: @Base.val.loc13_3 = internal constant { ptr, i32 } { ptr @"_CBase.MemberInit.$vtable", i32 3 }
+// CHECK:STDOUT: @Base.val.loc13_3 = internal constant <{ ptr, i32 }> <{ ptr @"_CBase.MemberInit.$vtable", i32 3 }>
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
 // CHECK:STDOUT: define void @_CFn.Base.MemberInit(ptr %self) #0 !dbg !4 {
@@ -486,22 +486,22 @@ fn Make() {
 // CHECK:STDOUT: define void @_CFn.MemberInit() #0 !dbg !11 {
 // CHECK:STDOUT: entry:
 // CHECK:STDOUT:   %i.var = alloca i32, align 4, !dbg !14
-// CHECK:STDOUT:   %v.var = alloca { ptr, i32 }, align 8, !dbg !15
-// CHECK:STDOUT:   %_.var = alloca { ptr, i32 }, align 8, !dbg !16
+// CHECK:STDOUT:   %v.var = alloca <{ ptr, i32 }>, align 8, !dbg !15
+// CHECK:STDOUT:   %_.var = alloca <{ ptr, i32 }>, align 8, !dbg !16
 // CHECK:STDOUT:   call void @llvm.lifetime.start.p0(ptr %i.var), !dbg !14
 // CHECK:STDOUT:   store i32 3, ptr %i.var, align 4, !dbg !14
 // CHECK:STDOUT:   call void @llvm.lifetime.start.p0(ptr %v.var), !dbg !15
-// CHECK:STDOUT:   %.loc11_24.2.vptr = getelementptr inbounds nuw { ptr, i32 }, ptr %v.var, i32 0, i32 0, !dbg !17
+// CHECK:STDOUT:   %.loc11_24.2.vptr = getelementptr inbounds nuw <{ ptr, i32 }>, ptr %v.var, i32 0, i32 0, !dbg !17
 // CHECK:STDOUT:   %.loc11_23 = load i32, ptr %i.var, align 4, !dbg !18
-// CHECK:STDOUT:   %.loc11_24.4.m = getelementptr inbounds nuw { ptr, i32 }, ptr %v.var, i32 0, i32 1, !dbg !17
+// CHECK:STDOUT:   %.loc11_24.4.m = getelementptr inbounds nuw <{ ptr, i32 }>, ptr %v.var, i32 0, i32 1, !dbg !17
 // CHECK:STDOUT:   store i32 %.loc11_23, ptr %.loc11_24.4.m, align 4, !dbg !17
 // CHECK:STDOUT:   store ptr @"_CBase.MemberInit.$vtable", ptr %.loc11_24.2.vptr, align 8, !dbg !17
-// CHECK:STDOUT:   %.loc12_4.m = getelementptr inbounds nuw { ptr, i32 }, ptr %v.var, i32 0, i32 1, !dbg !19
+// CHECK:STDOUT:   %.loc12_4.m = getelementptr inbounds nuw <{ ptr, i32 }>, ptr %v.var, i32 0, i32 1, !dbg !19
 // CHECK:STDOUT:   store i32 5, ptr %.loc12_4.m, align 4, !dbg !19
 // CHECK:STDOUT:   call void @llvm.lifetime.start.p0(ptr %_.var), !dbg !16
-// CHECK:STDOUT:   %.loc13_24.2.vptr = getelementptr inbounds nuw { ptr, i32 }, ptr %_.var, i32 0, i32 0, !dbg !20
-// CHECK:STDOUT:   %.loc13_24.5.m = getelementptr inbounds nuw { ptr, i32 }, ptr %_.var, i32 0, i32 1, !dbg !20
-// CHECK:STDOUT:   call void @llvm.memcpy.p0.p0.i64(ptr align 8 %_.var, ptr align 8 @Base.val.loc13_3, i64 16, i1 false), !dbg !16
+// CHECK:STDOUT:   %.loc13_24.2.vptr = getelementptr inbounds nuw <{ ptr, i32 }>, ptr %_.var, i32 0, i32 0, !dbg !20
+// CHECK:STDOUT:   %.loc13_24.5.m = getelementptr inbounds nuw <{ ptr, i32 }>, ptr %_.var, i32 0, i32 1, !dbg !20
+// CHECK:STDOUT:   call void @llvm.memcpy.p0.p0.i64(ptr align 1 %_.var, ptr align 1 @Base.val.loc13_3, i64 12, i1 false), !dbg !16
 // CHECK:STDOUT:   call void @"_COp.dbf7676be30a7aa8:core.Destroy.Core"(ptr %_.var), !dbg !16
 // CHECK:STDOUT:   call void @"_COp.dbf7676be30a7aa8:core.Destroy.Core"(ptr %v.var), !dbg !15
 // CHECK:STDOUT:   call void @"_COp.7e389eab4a7e5487:core.Destroy.Core"(ptr %i.var), !dbg !14
diff --git a/toolchain/lower/testdata/for/bindings.carbon b/toolchain/lower/testdata/for/bindings.carbon
index 10141c4b2680..b9b61e6dd1f7 100644
--- a/toolchain/lower/testdata/for/bindings.carbon
+++ b/toolchain/lower/testdata/for/bindings.carbon
@@ -43,7 +43,7 @@ fn For() {
 // CHECK:STDOUT: entry:
 // CHECK:STDOUT:   %r.var = alloca {}, align 8, !dbg !7
 // CHECK:STDOUT:   %var = alloca {}, align 8, !dbg !8
-// CHECK:STDOUT:   %.loc29_33.1.temp = alloca { { i32, i32 }, i1 }, align 8, !dbg !8
+// CHECK:STDOUT:   %.loc29_33.1.temp = alloca <{ { i32, i32 }, i1 }>, align 8, !dbg !8
 // CHECK:STDOUT:   %n.var = alloca i32, align 4, !dbg !9
 // CHECK:STDOUT:   %.loc29_33.8.temp = alloca { i32, i32 }, align 8, !dbg !8
 // CHECK:STDOUT:   call void @llvm.lifetime.start.p0(ptr %r.var), !dbg !7
@@ -133,7 +133,7 @@ fn For() {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr void @"_CNext.EmptyRange.1ccc388edee5a786.Main:Iterate.Core.8d745d19e7d6c4bd"(ptr sret({ { i32, i32 }, i1 }) %return, ptr %self, ptr %_) #0 !dbg !51 {
+// CHECK:STDOUT: define linkonce_odr void @"_CNext.EmptyRange.1ccc388edee5a786.Main:Iterate.Core.8d745d19e7d6c4bd"(ptr sret(<{ { i32, i32 }, i1 }>) %return, ptr %self, ptr %_) #0 !dbg !51 {
 // CHECK:STDOUT: entry:
 // CHECK:STDOUT:   call void @_CNone.Optional.Core.6b64456bb8003a40(ptr %return), !dbg !57
 // CHECK:STDOUT:   ret void, !dbg !58
@@ -152,14 +152,14 @@ fn For() {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr void @_CNone.Optional.Core.6b64456bb8003a40(ptr sret({ { i32, i32 }, i1 }) %return) #0 !dbg !72 {
+// CHECK:STDOUT: define linkonce_odr void @_CNone.Optional.Core.6b64456bb8003a40(ptr sret(<{ { i32, i32 }, i1 }>) %return) #0 !dbg !72 {
 // CHECK:STDOUT:   call void @"_CNone.3e8267224c5dc9c2:OptionalStorage.Core.8d745d19e7d6c4bd"(ptr %return), !dbg !75
 // CHECK:STDOUT:   ret void, !dbg !76
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
 // CHECK:STDOUT: define linkonce_odr i1 @"_CHas.3e8267224c5dc9c2:OptionalStorage.Core.8d745d19e7d6c4bd"(ptr %value) #0 !dbg !77 {
-// CHECK:STDOUT:   %has_value = getelementptr inbounds nuw { { i32, i32 }, i1 }, ptr %value, i32 0, i32 1, !dbg !80
+// CHECK:STDOUT:   %has_value = getelementptr inbounds nuw <{ { i32, i32 }, i1 }>, ptr %value, i32 0, i32 1, !dbg !80
 // CHECK:STDOUT:   %1 = load i8, ptr %has_value, align 1, !dbg !80
 // CHECK:STDOUT:   %2 = trunc i8 %1 to i1, !dbg !80
 // CHECK:STDOUT:   ret i1 %2, !dbg !81
@@ -167,14 +167,14 @@ fn For() {
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
 // CHECK:STDOUT: define linkonce_odr void @"_CGet.3e8267224c5dc9c2:OptionalStorage.Core.8d745d19e7d6c4bd"(ptr sret({ i32, i32 }) %return, ptr %value) #0 !dbg !82 {
-// CHECK:STDOUT:   %value1 = getelementptr inbounds nuw { { i32, i32 }, i1 }, ptr %value, i32 0, i32 0, !dbg !85
+// CHECK:STDOUT:   %value1 = getelementptr inbounds nuw <{ { i32, i32 }, i1 }>, ptr %value, i32 0, i32 0, !dbg !85
 // CHECK:STDOUT:   call void @"_COp.e4daa70d026fdea2:Copy.Core.3e36085cb869f630"(ptr %return, ptr %value1), !dbg !85
 // CHECK:STDOUT:   ret void, !dbg !86
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr void @"_CNone.3e8267224c5dc9c2:OptionalStorage.Core.8d745d19e7d6c4bd"(ptr sret({ { i32, i32 }, i1 }) %return) #0 !dbg !87 {
-// CHECK:STDOUT:   %has_value = getelementptr inbounds nuw { { i32, i32 }, i1 }, ptr %return, i32 0, i32 1, !dbg !88
+// CHECK:STDOUT: define linkonce_odr void @"_CNone.3e8267224c5dc9c2:OptionalStorage.Core.8d745d19e7d6c4bd"(ptr sret(<{ { i32, i32 }, i1 }>) %return) #0 !dbg !87 {
+// CHECK:STDOUT:   %has_value = getelementptr inbounds nuw <{ { i32, i32 }, i1 }>, ptr %return, i32 0, i32 1, !dbg !88
 // CHECK:STDOUT:   store i8 0, ptr %has_value, align 1, !dbg !88
 // CHECK:STDOUT:   ret void, !dbg !89
 // CHECK:STDOUT: }
diff --git a/toolchain/lower/testdata/for/break_continue.carbon b/toolchain/lower/testdata/for/break_continue.carbon
index 8c16f03fd956..0c7557b61299 100644
--- a/toolchain/lower/testdata/for/break_continue.carbon
+++ b/toolchain/lower/testdata/for/break_continue.carbon
@@ -38,7 +38,7 @@ fn For() {
 // CHECK:STDOUT: entry:
 // CHECK:STDOUT:   %.loc20_32.1.temp = alloca { i32, i32 }, align 8, !dbg !7
 // CHECK:STDOUT:   %var = alloca i32, align 4, !dbg !8
-// CHECK:STDOUT:   %.loc20_33.1.temp = alloca { i32, i1 }, align 8, !dbg !8
+// CHECK:STDOUT:   %.loc20_33.1.temp = alloca <{ i32, i1 }>, align 8, !dbg !8
 // CHECK:STDOUT:   call void @llvm.lifetime.start.p0(ptr %.loc20_32.1.temp), !dbg !7
 // CHECK:STDOUT:   call void @_CRange.Core(ptr %.loc20_32.1.temp, i32 100), !dbg !7
 // CHECK:STDOUT:   %IntRange.as.Iterate.impl.NewCursor.call = call i32 @"_CNewCursor.IntRange.9452f4c51951679b.Core:Iterate.Core.be1e879c1ad406d8"(ptr %.loc20_32.1.temp), !dbg !8
@@ -133,7 +133,7 @@ fn For() {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr void @"_CNext.IntRange.9452f4c51951679b.Core:Iterate.Core.be1e879c1ad406d8"(ptr sret({ i32, i1 }) %return, ptr %self, ptr %cursor) #0 !dbg !60 {
+// CHECK:STDOUT: define linkonce_odr void @"_CNext.IntRange.9452f4c51951679b.Core:Iterate.Core.be1e879c1ad406d8"(ptr sret(<{ i32, i1 }>) %return, ptr %self, ptr %cursor) #0 !dbg !60 {
 // CHECK:STDOUT:   %1 = alloca i32, align 4, !dbg !66
 // CHECK:STDOUT:   call void @llvm.lifetime.start.p0(ptr %1), !dbg !66
 // CHECK:STDOUT:   %2 = load i32, ptr %cursor, align 4, !dbg !67
@@ -178,20 +178,20 @@ fn For() {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr void @_CSome.Optional.Core.a0986cb4211ec3fb(ptr sret({ i32, i1 }) %return, i32 %value) #0 !dbg !96 {
+// CHECK:STDOUT: define linkonce_odr void @_CSome.Optional.Core.a0986cb4211ec3fb(ptr sret(<{ i32, i1 }>) %return, i32 %value) #0 !dbg !96 {
 // CHECK:STDOUT:   call void @"_CSome.3e8267224c5dc9c2:OptionalStorage.Core.0b1ea4541e2057b5"(ptr %return, i32 %value), !dbg !101
 // CHECK:STDOUT:   ret void, !dbg !102
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr void @_CNone.Optional.Core.a0986cb4211ec3fb(ptr sret({ i32, i1 }) %return) #0 !dbg !103 {
+// CHECK:STDOUT: define linkonce_odr void @_CNone.Optional.Core.a0986cb4211ec3fb(ptr sret(<{ i32, i1 }>) %return) #0 !dbg !103 {
 // CHECK:STDOUT:   call void @"_CNone.3e8267224c5dc9c2:OptionalStorage.Core.0b1ea4541e2057b5"(ptr %return), !dbg !106
 // CHECK:STDOUT:   ret void, !dbg !107
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
 // CHECK:STDOUT: define linkonce_odr i1 @"_CHas.3e8267224c5dc9c2:OptionalStorage.Core.0b1ea4541e2057b5"(ptr %value) #0 !dbg !108 {
-// CHECK:STDOUT:   %has_value = getelementptr inbounds nuw { i32, i1 }, ptr %value, i32 0, i32 1, !dbg !111
+// CHECK:STDOUT:   %has_value = getelementptr inbounds nuw <{ i32, i1 }>, ptr %value, i32 0, i32 1, !dbg !111
 // CHECK:STDOUT:   %1 = load i8, ptr %has_value, align 1, !dbg !111
 // CHECK:STDOUT:   %2 = trunc i8 %1 to i1, !dbg !111
 // CHECK:STDOUT:   ret i1 %2, !dbg !112
@@ -199,7 +199,7 @@ fn For() {
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
 // CHECK:STDOUT: define linkonce_odr i32 @"_CGet.3e8267224c5dc9c2:OptionalStorage.Core.0b1ea4541e2057b5"(ptr %value) #0 !dbg !113 {
-// CHECK:STDOUT:   %value1 = getelementptr inbounds nuw { i32, i1 }, ptr %value, i32 0, i32 0, !dbg !116
+// CHECK:STDOUT:   %value1 = getelementptr inbounds nuw <{ i32, i1 }>, ptr %value, i32 0, i32 0, !dbg !116
 // CHECK:STDOUT:   %1 = load i32, ptr %value1, align 4, !dbg !116
 // CHECK:STDOUT:   ret i32 %1, !dbg !117
 // CHECK:STDOUT: }
@@ -214,17 +214,17 @@ fn For() {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr void @"_CSome.3e8267224c5dc9c2:OptionalStorage.Core.0b1ea4541e2057b5"(ptr sret({ i32, i1 }) %return, i32 %self) #0 !dbg !126 {
-// CHECK:STDOUT:   %value = getelementptr inbounds nuw { i32, i1 }, ptr %return, i32 0, i32 0, !dbg !129
+// CHECK:STDOUT: define linkonce_odr void @"_CSome.3e8267224c5dc9c2:OptionalStorage.Core.0b1ea4541e2057b5"(ptr sret(<{ i32, i1 }>) %return, i32 %self) #0 !dbg !126 {
+// CHECK:STDOUT:   %value = getelementptr inbounds nuw <{ i32, i1 }>, ptr %return, i32 0, i32 0, !dbg !129
 // CHECK:STDOUT:   store i32 %self, ptr %value, align 4, !dbg !129
-// CHECK:STDOUT:   %has_value = getelementptr inbounds nuw { i32, i1 }, ptr %return, i32 0, i32 1, !dbg !130
+// CHECK:STDOUT:   %has_value = getelementptr inbounds nuw <{ i32, i1 }>, ptr %return, i32 0, i32 1, !dbg !130
 // CHECK:STDOUT:   store i8 1, ptr %has_value, align 1, !dbg !130
 // CHECK:STDOUT:   ret void, !dbg !131
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr void @"_CNone.3e8267224c5dc9c2:OptionalStorage.Core.0b1ea4541e2057b5"(ptr sret({ i32, i1 }) %return) #0 !dbg !132 {
-// CHECK:STDOUT:   %has_value = getelementptr inbounds nuw { i32, i1 }, ptr %return, i32 0, i32 1, !dbg !133
+// CHECK:STDOUT: define linkonce_odr void @"_CNone.3e8267224c5dc9c2:OptionalStorage.Core.0b1ea4541e2057b5"(ptr sret(<{ i32, i1 }>) %return) #0 !dbg !132 {
+// CHECK:STDOUT:   %has_value = getelementptr inbounds nuw <{ i32, i1 }>, ptr %return, i32 0, i32 1, !dbg !133
 // CHECK:STDOUT:   store i8 0, ptr %has_value, align 1, !dbg !133
 // CHECK:STDOUT:   ret void, !dbg !134
 // CHECK:STDOUT: }
diff --git a/toolchain/lower/testdata/for/for.carbon b/toolchain/lower/testdata/for/for.carbon
index 60e7a1a1253d..dddd3a6d37a0 100644
--- a/toolchain/lower/testdata/for/for.carbon
+++ b/toolchain/lower/testdata/for/for.carbon
@@ -38,7 +38,7 @@ fn For() {
 // CHECK:STDOUT: entry:
 // CHECK:STDOUT:   %.loc21_32.1.temp = alloca { i32, i32 }, align 8, !dbg !7
 // CHECK:STDOUT:   %var = alloca i32, align 4, !dbg !8
-// CHECK:STDOUT:   %.loc21_33.1.temp = alloca { i32, i1 }, align 8, !dbg !8
+// CHECK:STDOUT:   %.loc21_33.1.temp = alloca <{ i32, i1 }>, align 8, !dbg !8
 // CHECK:STDOUT:   call void @_CF.Main(), !dbg !9
 // CHECK:STDOUT:   call void @llvm.lifetime.start.p0(ptr %.loc21_32.1.temp), !dbg !7
 // CHECK:STDOUT:   call void @_CRange.Core(ptr %.loc21_32.1.temp, i32 100), !dbg !7
@@ -121,7 +121,7 @@ fn For() {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr void @"_CNext.IntRange.9452f4c51951679b.Core:Iterate.Core.be1e879c1ad406d8"(ptr sret({ i32, i1 }) %return, ptr %self, ptr %cursor) #0 !dbg !56 {
+// CHECK:STDOUT: define linkonce_odr void @"_CNext.IntRange.9452f4c51951679b.Core:Iterate.Core.be1e879c1ad406d8"(ptr sret(<{ i32, i1 }>) %return, ptr %self, ptr %cursor) #0 !dbg !56 {
 // CHECK:STDOUT:   %1 = alloca i32, align 4, !dbg !62
 // CHECK:STDOUT:   call void @llvm.lifetime.start.p0(ptr %1), !dbg !62
 // CHECK:STDOUT:   %2 = load i32, ptr %cursor, align 4, !dbg !63
@@ -166,20 +166,20 @@ fn For() {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr void @_CSome.Optional.Core.a0986cb4211ec3fb(ptr sret({ i32, i1 }) %return, i32 %value) #0 !dbg !92 {
+// CHECK:STDOUT: define linkonce_odr void @_CSome.Optional.Core.a0986cb4211ec3fb(ptr sret(<{ i32, i1 }>) %return, i32 %value) #0 !dbg !92 {
 // CHECK:STDOUT:   call void @"_CSome.3e8267224c5dc9c2:OptionalStorage.Core.0b1ea4541e2057b5"(ptr %return, i32 %value), !dbg !97
 // CHECK:STDOUT:   ret void, !dbg !98
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr void @_CNone.Optional.Core.a0986cb4211ec3fb(ptr sret({ i32, i1 }) %return) #0 !dbg !99 {
+// CHECK:STDOUT: define linkonce_odr void @_CNone.Optional.Core.a0986cb4211ec3fb(ptr sret(<{ i32, i1 }>) %return) #0 !dbg !99 {
 // CHECK:STDOUT:   call void @"_CNone.3e8267224c5dc9c2:OptionalStorage.Core.0b1ea4541e2057b5"(ptr %return), !dbg !102
 // CHECK:STDOUT:   ret void, !dbg !103
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
 // CHECK:STDOUT: define linkonce_odr i1 @"_CHas.3e8267224c5dc9c2:OptionalStorage.Core.0b1ea4541e2057b5"(ptr %value) #0 !dbg !104 {
-// CHECK:STDOUT:   %has_value = getelementptr inbounds nuw { i32, i1 }, ptr %value, i32 0, i32 1, !dbg !107
+// CHECK:STDOUT:   %has_value = getelementptr inbounds nuw <{ i32, i1 }>, ptr %value, i32 0, i32 1, !dbg !107
 // CHECK:STDOUT:   %1 = load i8, ptr %has_value, align 1, !dbg !107
 // CHECK:STDOUT:   %2 = trunc i8 %1 to i1, !dbg !107
 // CHECK:STDOUT:   ret i1 %2, !dbg !108
@@ -187,7 +187,7 @@ fn For() {
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
 // CHECK:STDOUT: define linkonce_odr i32 @"_CGet.3e8267224c5dc9c2:OptionalStorage.Core.0b1ea4541e2057b5"(ptr %value) #0 !dbg !109 {
-// CHECK:STDOUT:   %value1 = getelementptr inbounds nuw { i32, i1 }, ptr %value, i32 0, i32 0, !dbg !112
+// CHECK:STDOUT:   %value1 = getelementptr inbounds nuw <{ i32, i1 }>, ptr %value, i32 0, i32 0, !dbg !112
 // CHECK:STDOUT:   %1 = load i32, ptr %value1, align 4, !dbg !112
 // CHECK:STDOUT:   ret i32 %1, !dbg !113
 // CHECK:STDOUT: }
@@ -202,17 +202,17 @@ fn For() {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr void @"_CSome.3e8267224c5dc9c2:OptionalStorage.Core.0b1ea4541e2057b5"(ptr sret({ i32, i1 }) %return, i32 %self) #0 !dbg !122 {
-// CHECK:STDOUT:   %value = getelementptr inbounds nuw { i32, i1 }, ptr %return, i32 0, i32 0, !dbg !125
+// CHECK:STDOUT: define linkonce_odr void @"_CSome.3e8267224c5dc9c2:OptionalStorage.Core.0b1ea4541e2057b5"(ptr sret(<{ i32, i1 }>) %return, i32 %self) #0 !dbg !122 {
+// CHECK:STDOUT:   %value = getelementptr inbounds nuw <{ i32, i1 }>, ptr %return, i32 0, i32 0, !dbg !125
 // CHECK:STDOUT:   store i32 %self, ptr %value, align 4, !dbg !125
-// CHECK:STDOUT:   %has_value = getelementptr inbounds nuw { i32, i1 }, ptr %return, i32 0, i32 1, !dbg !126
+// CHECK:STDOUT:   %has_value = getelementptr inbounds nuw <{ i32, i1 }>, ptr %return, i32 0, i32 1, !dbg !126
 // CHECK:STDOUT:   store i8 1, ptr %has_value, align 1, !dbg !126
 // CHECK:STDOUT:   ret void, !dbg !127
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr void @"_CNone.3e8267224c5dc9c2:OptionalStorage.Core.0b1ea4541e2057b5"(ptr sret({ i32, i1 }) %return) #0 !dbg !128 {
-// CHECK:STDOUT:   %has_value = getelementptr inbounds nuw { i32, i1 }, ptr %return, i32 0, i32 1, !dbg !129
+// CHECK:STDOUT: define linkonce_odr void @"_CNone.3e8267224c5dc9c2:OptionalStorage.Core.0b1ea4541e2057b5"(ptr sret(<{ i32, i1 }>) %return) #0 !dbg !128 {
+// CHECK:STDOUT:   %has_value = getelementptr inbounds nuw <{ i32, i1 }>, ptr %return, i32 0, i32 1, !dbg !129
 // CHECK:STDOUT:   store i8 0, ptr %has_value, align 1, !dbg !129
 // CHECK:STDOUT:   ret void, !dbg !130
 // CHECK:STDOUT: }
diff --git a/toolchain/lower/testdata/primitives/optional.carbon b/toolchain/lower/testdata/primitives/optional.carbon
index 3eeab2b608e5..04c6eee125bf 100644
--- a/toolchain/lower/testdata/primitives/optional.carbon
+++ b/toolchain/lower/testdata/primitives/optional.carbon
@@ -41,7 +41,7 @@ fn AddOrRemoveConst(a: i32, b: const i32) {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define void @_CConvert.Main(ptr sret({ i32, i1 }) %return, ptr %o) #0 !dbg !11 {
+// CHECK:STDOUT: define void @_CConvert.Main(ptr sret(<{ i32, i1 }>) %return, ptr %o) #0 !dbg !11 {
 // CHECK:STDOUT: entry:
 // CHECK:STDOUT:   %Optional.HasValue.call = call i1 @_CHasValue.Optional.Core.03e3348579103d79(ptr %o), !dbg !17
 // CHECK:STDOUT:   br i1 %Optional.HasValue.call, label %if.then, label %if.else, !dbg !18
@@ -60,14 +60,14 @@ fn AddOrRemoveConst(a: i32, b: const i32) {
 // CHECK:STDOUT: ; Function Attrs: nounwind
 // CHECK:STDOUT: define void @_CAddOrRemoveConst.Main(i32 %a, i32 %b) #0 !dbg !24 {
 // CHECK:STDOUT: entry:
-// CHECK:STDOUT:   %_.var.loc24 = alloca { i32, i1 }, align 8, !dbg !30
-// CHECK:STDOUT:   %_.var.loc25 = alloca { i32, i1 }, align 8, !dbg !31
-// CHECK:STDOUT:   %_.var.loc26 = alloca { i32, i1 }, align 8, !dbg !32
-// CHECK:STDOUT:   %_.var.loc27 = alloca { i32, i1 }, align 8, !dbg !33
-// CHECK:STDOUT:   %_.var.loc28 = alloca { i32, i1 }, align 8, !dbg !34
-// CHECK:STDOUT:   %_.var.loc29 = alloca { i32, i1 }, align 8, !dbg !35
-// CHECK:STDOUT:   %_.var.loc30 = alloca { i32, i1 }, align 8, !dbg !36
-// CHECK:STDOUT:   %_.var.loc31 = alloca { i32, i1 }, align 8, !dbg !37
+// CHECK:STDOUT:   %_.var.loc24 = alloca <{ i32, i1 }>, align 8, !dbg !30
+// CHECK:STDOUT:   %_.var.loc25 = alloca <{ i32, i1 }>, align 8, !dbg !31
+// CHECK:STDOUT:   %_.var.loc26 = alloca <{ i32, i1 }>, align 8, !dbg !32
+// CHECK:STDOUT:   %_.var.loc27 = alloca <{ i32, i1 }>, align 8, !dbg !33
+// CHECK:STDOUT:   %_.var.loc28 = alloca <{ i32, i1 }>, align 8, !dbg !34
+// CHECK:STDOUT:   %_.var.loc29 = alloca <{ i32, i1 }>, align 8, !dbg !35
+// CHECK:STDOUT:   %_.var.loc30 = alloca <{ i32, i1 }>, align 8, !dbg !36
+// CHECK:STDOUT:   %_.var.loc31 = alloca <{ i32, i1 }>, align 8, !dbg !37
 // CHECK:STDOUT:   call void @llvm.lifetime.start.p0(ptr %_.var.loc24), !dbg !30
 // CHECK:STDOUT:   call void @"_CConvert.e5cf8fcbb4feaae2:ImplicitAs.0f95c9e18c91e00a.Core.6b1f19368d09e579"(ptr %_.var.loc24, i32 %a), !dbg !30
 // CHECK:STDOUT:   call void @llvm.lifetime.start.p0(ptr %_.var.loc25), !dbg !31
@@ -174,13 +174,13 @@ fn AddOrRemoveConst(a: i32, b: const i32) {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr void @"_CConvert.e5cf8fcbb4feaae2:ImplicitAs.0f95c9e18c91e00a.Core.6b1f19368d09e579"(ptr sret({ i32, i1 }) %return, i32 %self) #0 !dbg !96 {
+// CHECK:STDOUT: define linkonce_odr void @"_CConvert.e5cf8fcbb4feaae2:ImplicitAs.0f95c9e18c91e00a.Core.6b1f19368d09e579"(ptr sret(<{ i32, i1 }>) %return, i32 %self) #0 !dbg !96 {
 // CHECK:STDOUT:   call void @"_CConvert.90961d7b1ce4f089:OptionalAs.0e326e799dad0c64.Core.30ced37eb1e63547"(ptr %return, i32 %self), !dbg !101
 // CHECK:STDOUT:   ret void, !dbg !102
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr void @_CNone.Optional.Core.30ced37eb1e63547(ptr sret({ i32, i1 }) %return) #0 !dbg !103 {
+// CHECK:STDOUT: define linkonce_odr void @_CNone.Optional.Core.30ced37eb1e63547(ptr sret(<{ i32, i1 }>) %return) #0 !dbg !103 {
 // CHECK:STDOUT:   call void @"_CNone.3e8267224c5dc9c2:OptionalStorage.Core.bfb441135f07cbe1"(ptr %return), !dbg !106
 // CHECK:STDOUT:   ret void, !dbg !107
 // CHECK:STDOUT: }
@@ -189,43 +189,43 @@ fn AddOrRemoveConst(a: i32, b: const i32) {
 // CHECK:STDOUT: declare void @llvm.lifetime.start.p0(ptr captures(none)) #1
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr void @"_CConvert.a44fce96e16342e7:ImplicitAs.ad22d1bbc0605210.Core.77b263a5fd240ddf"(ptr sret({ i32, i1 }) %return, i32 %self) #0 !dbg !108 {
+// CHECK:STDOUT: define linkonce_odr void @"_CConvert.a44fce96e16342e7:ImplicitAs.ad22d1bbc0605210.Core.77b263a5fd240ddf"(ptr sret(<{ i32, i1 }>) %return, i32 %self) #0 !dbg !108 {
 // CHECK:STDOUT:   call void @"_CConvert.e5cf8fcbb4feaae2:ImplicitAs.0f95c9e18c91e00a.Core.6b1f19368d09e579"(ptr %return, i32 %self), !dbg !112
 // CHECK:STDOUT:   ret void, !dbg !113
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr void @"_CConvert.e5cf8fcbb4feaae2:ImplicitAs.0f95c9e18c91e00a.Core.787d589b54a95071"(ptr sret({ i32, i1 }) %return, i32 %self) #0 !dbg !114 {
+// CHECK:STDOUT: define linkonce_odr void @"_CConvert.e5cf8fcbb4feaae2:ImplicitAs.0f95c9e18c91e00a.Core.787d589b54a95071"(ptr sret(<{ i32, i1 }>) %return, i32 %self) #0 !dbg !114 {
 // CHECK:STDOUT:   call void @"_CConvert.3667eb502d1ddfa9:OptionalAs.c7a50af9bdd61b43.Core.5d35ad54738af8e4"(ptr %return, i32 %self), !dbg !117
 // CHECK:STDOUT:   ret void, !dbg !118
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr void @"_CConvert.a44fce96e16342e7:ImplicitAs.ad22d1bbc0605210.Core.25fb32d66f981ccd"(ptr sret({ i32, i1 }) %return, i32 %self) #0 !dbg !119 {
+// CHECK:STDOUT: define linkonce_odr void @"_CConvert.a44fce96e16342e7:ImplicitAs.ad22d1bbc0605210.Core.25fb32d66f981ccd"(ptr sret(<{ i32, i1 }>) %return, i32 %self) #0 !dbg !119 {
 // CHECK:STDOUT:   call void @"_CConvert.e5cf8fcbb4feaae2:ImplicitAs.0f95c9e18c91e00a.Core.787d589b54a95071"(ptr %return, i32 %self), !dbg !122
 // CHECK:STDOUT:   ret void, !dbg !123
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr void @"_CConvert.17f42c13d842b71d:ImplicitAs.eb057aa32837c84e.Core.77b263a5fd240ddf"(ptr sret({ i32, i1 }) %return, i32 %self) #0 !dbg !124 {
+// CHECK:STDOUT: define linkonce_odr void @"_CConvert.17f42c13d842b71d:ImplicitAs.eb057aa32837c84e.Core.77b263a5fd240ddf"(ptr sret(<{ i32, i1 }>) %return, i32 %self) #0 !dbg !124 {
 // CHECK:STDOUT:   call void @"_CConvert.e5cf8fcbb4feaae2:ImplicitAs.0f95c9e18c91e00a.Core.6b1f19368d09e579"(ptr %return, i32 %self), !dbg !127
 // CHECK:STDOUT:   ret void, !dbg !128
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr void @"_CConvert.17f42c13d842b71d:ImplicitAs.eb057aa32837c84e.Core.693532dcb04bf6dc"(ptr sret({ i32, i1 }) %return, i32 %self) #0 !dbg !129 {
+// CHECK:STDOUT: define linkonce_odr void @"_CConvert.17f42c13d842b71d:ImplicitAs.eb057aa32837c84e.Core.693532dcb04bf6dc"(ptr sret(<{ i32, i1 }>) %return, i32 %self) #0 !dbg !129 {
 // CHECK:STDOUT:   call void @"_CConvert.a44fce96e16342e7:ImplicitAs.ad22d1bbc0605210.Core.77b263a5fd240ddf"(ptr %return, i32 %self), !dbg !132
 // CHECK:STDOUT:   ret void, !dbg !133
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr void @"_CConvert.17f42c13d842b71d:ImplicitAs.eb057aa32837c84e.Core.25fb32d66f981ccd"(ptr sret({ i32, i1 }) %return, i32 %self) #0 !dbg !134 {
+// CHECK:STDOUT: define linkonce_odr void @"_CConvert.17f42c13d842b71d:ImplicitAs.eb057aa32837c84e.Core.25fb32d66f981ccd"(ptr sret(<{ i32, i1 }>) %return, i32 %self) #0 !dbg !134 {
 // CHECK:STDOUT:   call void @"_CConvert.e5cf8fcbb4feaae2:ImplicitAs.0f95c9e18c91e00a.Core.787d589b54a95071"(ptr %return, i32 %self), !dbg !137
 // CHECK:STDOUT:   ret void, !dbg !138
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr void @"_CConvert.17f42c13d842b71d:ImplicitAs.eb057aa32837c84e.Core.1c991c9fdfba671f"(ptr sret({ i32, i1 }) %return, i32 %self) #0 !dbg !139 {
+// CHECK:STDOUT: define linkonce_odr void @"_CConvert.17f42c13d842b71d:ImplicitAs.eb057aa32837c84e.Core.1c991c9fdfba671f"(ptr sret(<{ i32, i1 }>) %return, i32 %self) #0 !dbg !139 {
 // CHECK:STDOUT:   call void @"_CConvert.a44fce96e16342e7:ImplicitAs.ad22d1bbc0605210.Core.25fb32d66f981ccd"(ptr %return, i32 %self), !dbg !142
 // CHECK:STDOUT:   ret void, !dbg !143
 // CHECK:STDOUT: }
@@ -243,20 +243,20 @@ fn AddOrRemoveConst(a: i32, b: const i32) {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr void @"_CConvert.90961d7b1ce4f089:OptionalAs.0e326e799dad0c64.Core.30ced37eb1e63547"(ptr sret({ i32, i1 }) %return, i32 %self) #0 !dbg !154 {
+// CHECK:STDOUT: define linkonce_odr void @"_CConvert.90961d7b1ce4f089:OptionalAs.0e326e799dad0c64.Core.30ced37eb1e63547"(ptr sret(<{ i32, i1 }>) %return, i32 %self) #0 !dbg !154 {
 // CHECK:STDOUT:   call void @_CSome.Optional.Core.30ced37eb1e63547(ptr %return, i32 %self), !dbg !157
 // CHECK:STDOUT:   ret void, !dbg !158
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr void @"_CNone.3e8267224c5dc9c2:OptionalStorage.Core.bfb441135f07cbe1"(ptr sret({ i32, i1 }) %return) #0 !dbg !159 {
-// CHECK:STDOUT:   %has_value = getelementptr inbounds nuw { i32, i1 }, ptr %return, i32 0, i32 1, !dbg !160
+// CHECK:STDOUT: define linkonce_odr void @"_CNone.3e8267224c5dc9c2:OptionalStorage.Core.bfb441135f07cbe1"(ptr sret(<{ i32, i1 }>) %return) #0 !dbg !159 {
+// CHECK:STDOUT:   %has_value = getelementptr inbounds nuw <{ i32, i1 }>, ptr %return, i32 0, i32 1, !dbg !160
 // CHECK:STDOUT:   store i8 0, ptr %has_value, align 1, !dbg !160
 // CHECK:STDOUT:   ret void, !dbg !161
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr void @"_CConvert.3667eb502d1ddfa9:OptionalAs.c7a50af9bdd61b43.Core.5d35ad54738af8e4"(ptr sret({ i32, i1 }) %return, i32 %self) #0 !dbg !162 {
+// CHECK:STDOUT: define linkonce_odr void @"_CConvert.3667eb502d1ddfa9:OptionalAs.c7a50af9bdd61b43.Core.5d35ad54738af8e4"(ptr sret(<{ i32, i1 }>) %return, i32 %self) #0 !dbg !162 {
 // CHECK:STDOUT:   %temp = alloca i32, align 4, !dbg !165
 // CHECK:STDOUT:   call void @llvm.lifetime.start.p0(ptr %temp), !dbg !165
 // CHECK:STDOUT:   %1 = call i32 @"_CConvert.a44fce96e16342e7:ImplicitAs.ad22d1bbc0605210.Core.90a4f5ca3e06badd"(i32 %self), !dbg !165
@@ -268,7 +268,7 @@ fn AddOrRemoveConst(a: i32, b: const i32) {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr void @_CSome.Optional.Core.30ced37eb1e63547(ptr sret({ i32, i1 }) %return, i32 %value) #0 !dbg !168 {
+// CHECK:STDOUT: define linkonce_odr void @_CSome.Optional.Core.30ced37eb1e63547(ptr sret(<{ i32, i1 }>) %return, i32 %value) #0 !dbg !168 {
 // CHECK:STDOUT:   call void @"_CSome.3e8267224c5dc9c2:OptionalStorage.Core.bfb441135f07cbe1"(ptr %return, i32 %value), !dbg !171
 // CHECK:STDOUT:   ret void, !dbg !172
 // CHECK:STDOUT: }
@@ -280,16 +280,16 @@ fn AddOrRemoveConst(a: i32, b: const i32) {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr void @_CSome.Optional.Core.b0246d3dd29c9210(ptr sret({ i32, i1 }) %return, i32 %value) #0 !dbg !178 {
+// CHECK:STDOUT: define linkonce_odr void @_CSome.Optional.Core.b0246d3dd29c9210(ptr sret(<{ i32, i1 }>) %return, i32 %value) #0 !dbg !178 {
 // CHECK:STDOUT:   call void @"_CSome.3e8267224c5dc9c2:OptionalStorage.Core.5325ffa2b57e13bd"(ptr %return, i32 %value), !dbg !181
 // CHECK:STDOUT:   ret void, !dbg !182
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr void @"_CSome.3e8267224c5dc9c2:OptionalStorage.Core.bfb441135f07cbe1"(ptr sret({ i32, i1 }) %return, i32 %self) #0 !dbg !183 {
-// CHECK:STDOUT:   %value = getelementptr inbounds nuw { i32, i1 }, ptr %return, i32 0, i32 0, !dbg !186
+// CHECK:STDOUT: define linkonce_odr void @"_CSome.3e8267224c5dc9c2:OptionalStorage.Core.bfb441135f07cbe1"(ptr sret(<{ i32, i1 }>) %return, i32 %self) #0 !dbg !183 {
+// CHECK:STDOUT:   %value = getelementptr inbounds nuw <{ i32, i1 }>, ptr %return, i32 0, i32 0, !dbg !186
 // CHECK:STDOUT:   store i32 %self, ptr %value, align 4, !dbg !186
-// CHECK:STDOUT:   %has_value = getelementptr inbounds nuw { i32, i1 }, ptr %return, i32 0, i32 1, !dbg !187
+// CHECK:STDOUT:   %has_value = getelementptr inbounds nuw <{ i32, i1 }>, ptr %return, i32 0, i32 1, !dbg !187
 // CHECK:STDOUT:   store i8 1, ptr %has_value, align 1, !dbg !187
 // CHECK:STDOUT:   ret void, !dbg !188
 // CHECK:STDOUT: }
@@ -301,11 +301,11 @@ fn AddOrRemoveConst(a: i32, b: const i32) {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr void @"_CSome.3e8267224c5dc9c2:OptionalStorage.Core.5325ffa2b57e13bd"(ptr sret({ i32, i1 }) %return, i32 %self) #0 !dbg !197 {
-// CHECK:STDOUT:   %value = getelementptr inbounds nuw { i32, i1 }, ptr %return, i32 0, i32 0, !dbg !200
+// CHECK:STDOUT: define linkonce_odr void @"_CSome.3e8267224c5dc9c2:OptionalStorage.Core.5325ffa2b57e13bd"(ptr sret(<{ i32, i1 }>) %return, i32 %self) #0 !dbg !197 {
+// CHECK:STDOUT:   %value = getelementptr inbounds nuw <{ i32, i1 }>, ptr %return, i32 0, i32 0, !dbg !200
 // CHECK:STDOUT:   %1 = call i32 @"_COp.34e7a685d3648824:Copy.Core.64ccbb8e5d9a0b8e"(i32 %self), !dbg !201
 // CHECK:STDOUT:   store i32 %1, ptr %value, align 4, !dbg !200
-// CHECK:STDOUT:   %has_value = getelementptr inbounds nuw { i32, i1 }, ptr %return, i32 0, i32 1, !dbg !202
+// CHECK:STDOUT:   %has_value = getelementptr inbounds nuw <{ i32, i1 }>, ptr %return, i32 0, i32 1, !dbg !202
 // CHECK:STDOUT:   store i8 1, ptr %has_value, align 1, !dbg !202
 // CHECK:STDOUT:   ret void, !dbg !203
 // CHECK:STDOUT: }
diff --git a/toolchain/lower/testdata/struct/layout.carbon b/toolchain/lower/testdata/struct/layout.carbon
new file mode 100644
index 000000000000..62a7adab02ae
--- /dev/null
+++ b/toolchain/lower/testdata/struct/layout.carbon
@@ -0,0 +1,433 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// INCLUDE-FILE: toolchain/testing/testdata/min_prelude/int.carbon
+//
+// AUTOUPDATE
+// TIP: To test this file alone, run:
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/lower/testdata/struct/layout.carbon
+// TIP: To dump output, run:
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/struct/layout.carbon
+
+// --- no_padding.carbon
+library "[[@TEST_NAME]]";
+
+fn G(p: i32*);
+
+fn F() {
+  // LLVM {i32, i32, i32} matches the Carbon layout, so we use it.
+  var no_padding: {.x: i32, .y: i32, .z: i32};
+  G(&no_padding.x);
+  G(&no_padding.y);
+  G(&no_padding.z);
+}
+
+// --- avoid_tail_padding.carbon
+library "[[@TEST_NAME]]";
+
+fn G(p: i32*);
+
+fn F() {
+  // LLVM {ptr, i32} would have a size of 16, so we use a packed struct.
+  var avoid_tail_padding: {.x: ()*, .y: i32};
+  G(&avoid_tail_padding.y);
+}
+
+// --- use_tail_padding.carbon
+library "[[@TEST_NAME]]";
+
+fn G(p: i32*);
+
+fn F() {
+  // LLVM {ptr, i32} would have a size of 16, so we use a packed struct as the
+  // type of `.a`. `.b` goes in the tail padding.
+  var use_tail_padding: {.a: {.x: ()*, .y: i32}, .b: i32};
+  G(&use_tail_padding.a.y);
+  G(&use_tail_padding.b);
+}
+
+// --- implicit_padding.carbon
+library "[[@TEST_NAME]]";
+
+fn G(p: ()**);
+
+fn F() {
+  // LLVM {<{ptr, i32}>, ptr} inserts the right padding before `.b`, so we use
+  // it directly.
+  var implicit_padding: {.a: {.x: ()*, .y: i32}, .b: ()*};
+  G(&implicit_padding.a.x);
+  G(&implicit_padding.b);
+}
+
+// --- insert_padding.carbon
+library "[[@TEST_NAME]]";
+
+fn G(p: ()**);
+
+fn F() {
+  // LLVM {<{i32, i32, i32}>, ptr, i32} would have extra tail padding, so we use
+  // a packed struct. That requires that we explicitly add padding between `.a`
+  // and `.b`.
+  var insert_padding: {.a: {.x: i32, .y: i32, .z: i32}, .b: ()*, .c: i32};
+  G(&insert_padding.b);
+}
+
+// CHECK:STDOUT: ; ModuleID = 'no_padding.carbon'
+// CHECK:STDOUT: source_filename = "no_padding.carbon"
+// CHECK:STDOUT:
+// CHECK:STDOUT: declare void @_CG.Main(ptr)
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nounwind
+// CHECK:STDOUT: define void @_CF.Main() #0 !dbg !4 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %no_padding.var = alloca { i32, i32, i32 }, align 8, !dbg !7
+// CHECK:STDOUT:   call void @llvm.lifetime.start.p0(ptr %no_padding.var), !dbg !7
+// CHECK:STDOUT:   %.loc8.x = getelementptr inbounds nuw { i32, i32, i32 }, ptr %no_padding.var, i32 0, i32 0, !dbg !8
+// CHECK:STDOUT:   call void @_CG.Main(ptr %.loc8.x), !dbg !9
+// CHECK:STDOUT:   %.loc9.y = getelementptr inbounds nuw { i32, i32, i32 }, ptr %no_padding.var, i32 0, i32 1, !dbg !10
+// CHECK:STDOUT:   call void @_CG.Main(ptr %.loc9.y), !dbg !11
+// CHECK:STDOUT:   %.loc10.z = getelementptr inbounds nuw { i32, i32, i32 }, ptr %no_padding.var, i32 0, i32 2, !dbg !12
+// CHECK:STDOUT:   call void @_CG.Main(ptr %.loc10.z), !dbg !13
+// CHECK:STDOUT:   call void @"_COp.3124a28397dbe9e9:core.Destroy.Core"(ptr %no_padding.var), !dbg !7
+// CHECK:STDOUT:   ret void, !dbg !14
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nounwind
+// CHECK:STDOUT: define weak_odr void @"_COp.7e389eab4a7e5487:core.Destroy.Core"(ptr %self) #0 !dbg !15 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   ret void, !dbg !21
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nounwind
+// CHECK:STDOUT: define weak_odr void @"_COp.3124a28397dbe9e9:core.Destroy.Core"(ptr %self) #0 !dbg !22 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   ret void, !dbg !28
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nocallback nofree nosync nounwind willreturn memory(argmem: readwrite)
+// CHECK:STDOUT: declare void @llvm.lifetime.start.p0(ptr captures(none)) #1
+// CHECK:STDOUT:
+// CHECK:STDOUT: attributes #0 = { nounwind }
+// CHECK:STDOUT: attributes #1 = { nocallback nofree nosync nounwind willreturn memory(argmem: readwrite) }
+// CHECK:STDOUT:
+// CHECK:STDOUT: !llvm.module.flags = !{!0, !1}
+// CHECK:STDOUT: !llvm.dbg.cu = !{!2}
+// CHECK:STDOUT:
+// CHECK:STDOUT: !0 = !{i32 7, !"Dwarf Version", i32 5}
+// CHECK:STDOUT: !1 = !{i32 2, !"Debug Info Version", i32 3}
+// CHECK:STDOUT: !2 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !3, producer: "carbon", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug)
+// CHECK:STDOUT: !3 = !DIFile(filename: "no_padding.carbon", directory: "")
+// CHECK:STDOUT: !4 = distinct !DISubprogram(name: "F", linkageName: "_CF.Main", scope: null, file: !3, line: 5, type: !5, spFlags: DISPFlagDefinition, unit: !2)
+// CHECK:STDOUT: !5 = !DISubroutineType(types: !6)
+// CHECK:STDOUT: !6 = !{null}
+// CHECK:STDOUT: !7 = !DILocation(line: 7, column: 3, scope: !4)
+// CHECK:STDOUT: !8 = !DILocation(line: 8, column: 6, scope: !4)
+// CHECK:STDOUT: !9 = !DILocation(line: 8, column: 3, scope: !4)
+// CHECK:STDOUT: !10 = !DILocation(line: 9, column: 6, scope: !4)
+// CHECK:STDOUT: !11 = !DILocation(line: 9, column: 3, scope: !4)
+// CHECK:STDOUT: !12 = !DILocation(line: 10, column: 6, scope: !4)
+// CHECK:STDOUT: !13 = !DILocation(line: 10, column: 3, scope: !4)
+// CHECK:STDOUT: !14 = !DILocation(line: 5, column: 1, scope: !4)
+// CHECK:STDOUT: !15 = distinct !DISubprogram(name: "Op", linkageName: "_COp.7e389eab4a7e5487:core.Destroy.Core", scope: null, file: !3, line: 7, type: !16, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !19)
+// CHECK:STDOUT: !16 = !DISubroutineType(types: !17)
+// CHECK:STDOUT: !17 = !{null, !18}
+// CHECK:STDOUT: !18 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+// CHECK:STDOUT: !19 = !{!20}
+// CHECK:STDOUT: !20 = !DILocalVariable(arg: 1, scope: !15, type: !18)
+// CHECK:STDOUT: !21 = !DILocation(line: 7, column: 3, scope: !15)
+// CHECK:STDOUT: !22 = distinct !DISubprogram(name: "Op", linkageName: "_COp.3124a28397dbe9e9:core.Destroy.Core", scope: null, file: !3, line: 7, type: !23, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !26)
+// CHECK:STDOUT: !23 = !DISubroutineType(types: !24)
+// CHECK:STDOUT: !24 = !{null, !25}
+// CHECK:STDOUT: !25 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: null, size: 64)
+// CHECK:STDOUT: !26 = !{!27}
+// CHECK:STDOUT: !27 = !DILocalVariable(arg: 1, scope: !22, type: !25)
+// CHECK:STDOUT: !28 = !DILocation(line: 7, column: 3, scope: !22)
+// CHECK:STDOUT: ; ModuleID = 'avoid_tail_padding.carbon'
+// CHECK:STDOUT: source_filename = "avoid_tail_padding.carbon"
+// CHECK:STDOUT:
+// CHECK:STDOUT: declare void @_CG.Main(ptr)
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nounwind
+// CHECK:STDOUT: define void @_CF.Main() #0 !dbg !4 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %avoid_tail_padding.var = alloca <{ ptr, i32 }>, align 8, !dbg !7
+// CHECK:STDOUT:   call void @llvm.lifetime.start.p0(ptr %avoid_tail_padding.var), !dbg !7
+// CHECK:STDOUT:   %.loc8.y = getelementptr inbounds nuw <{ ptr, i32 }>, ptr %avoid_tail_padding.var, i32 0, i32 1, !dbg !8
+// CHECK:STDOUT:   call void @_CG.Main(ptr %.loc8.y), !dbg !9
+// CHECK:STDOUT:   call void @"_COp.0d530a9b810c77a1:core.Destroy.Core"(ptr %avoid_tail_padding.var), !dbg !7
+// CHECK:STDOUT:   ret void, !dbg !10
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nounwind
+// CHECK:STDOUT: define weak_odr void @"_COp.7e389eab4a7e5487:core.Destroy.Core"(ptr %self) #0 !dbg !11 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   ret void, !dbg !17
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nounwind
+// CHECK:STDOUT: define weak_odr void @"_COp.0d530a9b810c77a1:core.Destroy.Core"(ptr %self) #0 !dbg !18 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   ret void, !dbg !24
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nocallback nofree nosync nounwind willreturn memory(argmem: readwrite)
+// CHECK:STDOUT: declare void @llvm.lifetime.start.p0(ptr captures(none)) #1
+// CHECK:STDOUT:
+// CHECK:STDOUT: attributes #0 = { nounwind }
+// CHECK:STDOUT: attributes #1 = { nocallback nofree nosync nounwind willreturn memory(argmem: readwrite) }
+// CHECK:STDOUT:
+// CHECK:STDOUT: !llvm.module.flags = !{!0, !1}
+// CHECK:STDOUT: !llvm.dbg.cu = !{!2}
+// CHECK:STDOUT:
+// CHECK:STDOUT: !0 = !{i32 7, !"Dwarf Version", i32 5}
+// CHECK:STDOUT: !1 = !{i32 2, !"Debug Info Version", i32 3}
+// CHECK:STDOUT: !2 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !3, producer: "carbon", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug)
+// CHECK:STDOUT: !3 = !DIFile(filename: "avoid_tail_padding.carbon", directory: "")
+// CHECK:STDOUT: !4 = distinct !DISubprogram(name: "F", linkageName: "_CF.Main", scope: null, file: !3, line: 5, type: !5, spFlags: DISPFlagDefinition, unit: !2)
+// CHECK:STDOUT: !5 = !DISubroutineType(types: !6)
+// CHECK:STDOUT: !6 = !{null}
+// CHECK:STDOUT: !7 = !DILocation(line: 7, column: 3, scope: !4)
+// CHECK:STDOUT: !8 = !DILocation(line: 8, column: 6, scope: !4)
+// CHECK:STDOUT: !9 = !DILocation(line: 8, column: 3, scope: !4)
+// CHECK:STDOUT: !10 = !DILocation(line: 5, column: 1, scope: !4)
+// CHECK:STDOUT: !11 = distinct !DISubprogram(name: "Op", linkageName: "_COp.7e389eab4a7e5487:core.Destroy.Core", scope: null, file: !3, line: 7, type: !12, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !15)
+// CHECK:STDOUT: !12 = !DISubroutineType(types: !13)
+// CHECK:STDOUT: !13 = !{null, !14}
+// CHECK:STDOUT: !14 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+// CHECK:STDOUT: !15 = !{!16}
+// CHECK:STDOUT: !16 = !DILocalVariable(arg: 1, scope: !11, type: !14)
+// CHECK:STDOUT: !17 = !DILocation(line: 7, column: 3, scope: !11)
+// CHECK:STDOUT: !18 = distinct !DISubprogram(name: "Op", linkageName: "_COp.0d530a9b810c77a1:core.Destroy.Core", scope: null, file: !3, line: 7, type: !19, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !22)
+// CHECK:STDOUT: !19 = !DISubroutineType(types: !20)
+// CHECK:STDOUT: !20 = !{null, !21}
+// CHECK:STDOUT: !21 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: null, size: 64)
+// CHECK:STDOUT: !22 = !{!23}
+// CHECK:STDOUT: !23 = !DILocalVariable(arg: 1, scope: !18, type: !21)
+// CHECK:STDOUT: !24 = !DILocation(line: 7, column: 3, scope: !18)
+// CHECK:STDOUT: ; ModuleID = 'use_tail_padding.carbon'
+// CHECK:STDOUT: source_filename = "use_tail_padding.carbon"
+// CHECK:STDOUT:
+// CHECK:STDOUT: declare void @_CG.Main(ptr)
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nounwind
+// CHECK:STDOUT: define void @_CF.Main() #0 !dbg !4 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %use_tail_padding.var = alloca { <{ ptr, i32 }>, i32 }, align 8, !dbg !7
+// CHECK:STDOUT:   call void @llvm.lifetime.start.p0(ptr %use_tail_padding.var), !dbg !7
+// CHECK:STDOUT:   %.loc9_22.a = getelementptr inbounds nuw { <{ ptr, i32 }>, i32 }, ptr %use_tail_padding.var, i32 0, i32 0, !dbg !8
+// CHECK:STDOUT:   %.loc9_24.y = getelementptr inbounds nuw <{ ptr, i32 }>, ptr %.loc9_22.a, i32 0, i32 1, !dbg !8
+// CHECK:STDOUT:   call void @_CG.Main(ptr %.loc9_24.y), !dbg !9
+// CHECK:STDOUT:   %.loc10.b = getelementptr inbounds nuw { <{ ptr, i32 }>, i32 }, ptr %use_tail_padding.var, i32 0, i32 1, !dbg !10
+// CHECK:STDOUT:   call void @_CG.Main(ptr %.loc10.b), !dbg !11
+// CHECK:STDOUT:   call void @"_COp.2106667af8a21f02:core.Destroy.Core"(ptr %use_tail_padding.var), !dbg !7
+// CHECK:STDOUT:   ret void, !dbg !12
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nounwind
+// CHECK:STDOUT: define weak_odr void @"_COp.7e389eab4a7e5487:core.Destroy.Core"(ptr %self) #0 !dbg !13 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   ret void, !dbg !19
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nounwind
+// CHECK:STDOUT: define weak_odr void @"_COp.0d530a9b810c77a1:core.Destroy.Core"(ptr %self) #0 !dbg !20 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   ret void, !dbg !26
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nounwind
+// CHECK:STDOUT: define weak_odr void @"_COp.2106667af8a21f02:core.Destroy.Core"(ptr %self) #0 !dbg !27 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   ret void, !dbg !30
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nocallback nofree nosync nounwind willreturn memory(argmem: readwrite)
+// CHECK:STDOUT: declare void @llvm.lifetime.start.p0(ptr captures(none)) #1
+// CHECK:STDOUT:
+// CHECK:STDOUT: attributes #0 = { nounwind }
+// CHECK:STDOUT: attributes #1 = { nocallback nofree nosync nounwind willreturn memory(argmem: readwrite) }
+// CHECK:STDOUT:
+// CHECK:STDOUT: !llvm.module.flags = !{!0, !1}
+// CHECK:STDOUT: !llvm.dbg.cu = !{!2}
+// CHECK:STDOUT:
+// CHECK:STDOUT: !0 = !{i32 7, !"Dwarf Version", i32 5}
+// CHECK:STDOUT: !1 = !{i32 2, !"Debug Info Version", i32 3}
+// CHECK:STDOUT: !2 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !3, producer: "carbon", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug)
+// CHECK:STDOUT: !3 = !DIFile(filename: "use_tail_padding.carbon", directory: "")
+// CHECK:STDOUT: !4 = distinct !DISubprogram(name: "F", linkageName: "_CF.Main", scope: null, file: !3, line: 5, type: !5, spFlags: DISPFlagDefinition, unit: !2)
+// CHECK:STDOUT: !5 = !DISubroutineType(types: !6)
+// CHECK:STDOUT: !6 = !{null}
+// CHECK:STDOUT: !7 = !DILocation(line: 8, column: 3, scope: !4)
+// CHECK:STDOUT: !8 = !DILocation(line: 9, column: 6, scope: !4)
+// CHECK:STDOUT: !9 = !DILocation(line: 9, column: 3, scope: !4)
+// CHECK:STDOUT: !10 = !DILocation(line: 10, column: 6, scope: !4)
+// CHECK:STDOUT: !11 = !DILocation(line: 10, column: 3, scope: !4)
+// CHECK:STDOUT: !12 = !DILocation(line: 5, column: 1, scope: !4)
+// CHECK:STDOUT: !13 = distinct !DISubprogram(name: "Op", linkageName: "_COp.7e389eab4a7e5487:core.Destroy.Core", scope: null, file: !3, line: 8, type: !14, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !17)
+// CHECK:STDOUT: !14 = !DISubroutineType(types: !15)
+// CHECK:STDOUT: !15 = !{null, !16}
+// CHECK:STDOUT: !16 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+// CHECK:STDOUT: !17 = !{!18}
+// CHECK:STDOUT: !18 = !DILocalVariable(arg: 1, scope: !13, type: !16)
+// CHECK:STDOUT: !19 = !DILocation(line: 8, column: 3, scope: !13)
+// CHECK:STDOUT: !20 = distinct !DISubprogram(name: "Op", linkageName: "_COp.0d530a9b810c77a1:core.Destroy.Core", scope: null, file: !3, line: 8, type: !21, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !24)
+// CHECK:STDOUT: !21 = !DISubroutineType(types: !22)
+// CHECK:STDOUT: !22 = !{null, !23}
+// CHECK:STDOUT: !23 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: null, size: 64)
+// CHECK:STDOUT: !24 = !{!25}
+// CHECK:STDOUT: !25 = !DILocalVariable(arg: 1, scope: !20, type: !23)
+// CHECK:STDOUT: !26 = !DILocation(line: 8, column: 3, scope: !20)
+// CHECK:STDOUT: !27 = distinct !DISubprogram(name: "Op", linkageName: "_COp.2106667af8a21f02:core.Destroy.Core", scope: null, file: !3, line: 8, type: !21, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !28)
+// CHECK:STDOUT: !28 = !{!29}
+// CHECK:STDOUT: !29 = !DILocalVariable(arg: 1, scope: !27, type: !23)
+// CHECK:STDOUT: !30 = !DILocation(line: 8, column: 3, scope: !27)
+// CHECK:STDOUT: ; ModuleID = 'implicit_padding.carbon'
+// CHECK:STDOUT: source_filename = "implicit_padding.carbon"
+// CHECK:STDOUT:
+// CHECK:STDOUT: declare void @_CG.Main(ptr)
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nounwind
+// CHECK:STDOUT: define void @_CF.Main() #0 !dbg !4 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %implicit_padding.var = alloca { <{ ptr, i32 }>, ptr }, align 8, !dbg !7
+// CHECK:STDOUT:   call void @llvm.lifetime.start.p0(ptr %implicit_padding.var), !dbg !7
+// CHECK:STDOUT:   %.loc9_22.a = getelementptr inbounds nuw { <{ ptr, i32 }>, ptr }, ptr %implicit_padding.var, i32 0, i32 0, !dbg !8
+// CHECK:STDOUT:   %.loc9_24.x = getelementptr inbounds nuw <{ ptr, i32 }>, ptr %.loc9_22.a, i32 0, i32 0, !dbg !8
+// CHECK:STDOUT:   call void @_CG.Main(ptr %.loc9_24.x), !dbg !9
+// CHECK:STDOUT:   %.loc10.b = getelementptr inbounds nuw { <{ ptr, i32 }>, ptr }, ptr %implicit_padding.var, i32 0, i32 1, !dbg !10
+// CHECK:STDOUT:   call void @_CG.Main(ptr %.loc10.b), !dbg !11
+// CHECK:STDOUT:   call void @"_COp.a17d504d00302116:core.Destroy.Core"(ptr %implicit_padding.var), !dbg !7
+// CHECK:STDOUT:   ret void, !dbg !12
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nounwind
+// CHECK:STDOUT: define weak_odr void @"_COp.7e389eab4a7e5487:core.Destroy.Core"(ptr %self) #0 !dbg !13 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   ret void, !dbg !19
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nounwind
+// CHECK:STDOUT: define weak_odr void @"_COp.0d530a9b810c77a1:core.Destroy.Core"(ptr %self) #0 !dbg !20 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   ret void, !dbg !26
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nounwind
+// CHECK:STDOUT: define weak_odr void @"_COp.a17d504d00302116:core.Destroy.Core"(ptr %self) #0 !dbg !27 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   ret void, !dbg !30
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nocallback nofree nosync nounwind willreturn memory(argmem: readwrite)
+// CHECK:STDOUT: declare void @llvm.lifetime.start.p0(ptr captures(none)) #1
+// CHECK:STDOUT:
+// CHECK:STDOUT: attributes #0 = { nounwind }
+// CHECK:STDOUT: attributes #1 = { nocallback nofree nosync nounwind willreturn memory(argmem: readwrite) }
+// CHECK:STDOUT:
+// CHECK:STDOUT: !llvm.module.flags = !{!0, !1}
+// CHECK:STDOUT: !llvm.dbg.cu = !{!2}
+// CHECK:STDOUT:
+// CHECK:STDOUT: !0 = !{i32 7, !"Dwarf Version", i32 5}
+// CHECK:STDOUT: !1 = !{i32 2, !"Debug Info Version", i32 3}
+// CHECK:STDOUT: !2 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !3, producer: "carbon", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug)
+// CHECK:STDOUT: !3 = !DIFile(filename: "implicit_padding.carbon", directory: "")
+// CHECK:STDOUT: !4 = distinct !DISubprogram(name: "F", linkageName: "_CF.Main", scope: null, file: !3, line: 5, type: !5, spFlags: DISPFlagDefinition, unit: !2)
+// CHECK:STDOUT: !5 = !DISubroutineType(types: !6)
+// CHECK:STDOUT: !6 = !{null}
+// CHECK:STDOUT: !7 = !DILocation(line: 8, column: 3, scope: !4)
+// CHECK:STDOUT: !8 = !DILocation(line: 9, column: 6, scope: !4)
+// CHECK:STDOUT: !9 = !DILocation(line: 9, column: 3, scope: !4)
+// CHECK:STDOUT: !10 = !DILocation(line: 10, column: 6, scope: !4)
+// CHECK:STDOUT: !11 = !DILocation(line: 10, column: 3, scope: !4)
+// CHECK:STDOUT: !12 = !DILocation(line: 5, column: 1, scope: !4)
+// CHECK:STDOUT: !13 = distinct !DISubprogram(name: "Op", linkageName: "_COp.7e389eab4a7e5487:core.Destroy.Core", scope: null, file: !3, line: 8, type: !14, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !17)
+// CHECK:STDOUT: !14 = !DISubroutineType(types: !15)
+// CHECK:STDOUT: !15 = !{null, !16}
+// CHECK:STDOUT: !16 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+// CHECK:STDOUT: !17 = !{!18}
+// CHECK:STDOUT: !18 = !DILocalVariable(arg: 1, scope: !13, type: !16)
+// CHECK:STDOUT: !19 = !DILocation(line: 8, column: 3, scope: !13)
+// CHECK:STDOUT: !20 = distinct !DISubprogram(name: "Op", linkageName: "_COp.0d530a9b810c77a1:core.Destroy.Core", scope: null, file: !3, line: 8, type: !21, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !24)
+// CHECK:STDOUT: !21 = !DISubroutineType(types: !22)
+// CHECK:STDOUT: !22 = !{null, !23}
+// CHECK:STDOUT: !23 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: null, size: 64)
+// CHECK:STDOUT: !24 = !{!25}
+// CHECK:STDOUT: !25 = !DILocalVariable(arg: 1, scope: !20, type: !23)
+// CHECK:STDOUT: !26 = !DILocation(line: 8, column: 3, scope: !20)
+// CHECK:STDOUT: !27 = distinct !DISubprogram(name: "Op", linkageName: "_COp.a17d504d00302116:core.Destroy.Core", scope: null, file: !3, line: 8, type: !21, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !28)
+// CHECK:STDOUT: !28 = !{!29}
+// CHECK:STDOUT: !29 = !DILocalVariable(arg: 1, scope: !27, type: !23)
+// CHECK:STDOUT: !30 = !DILocation(line: 8, column: 3, scope: !27)
+// CHECK:STDOUT: ; ModuleID = 'insert_padding.carbon'
+// CHECK:STDOUT: source_filename = "insert_padding.carbon"
+// CHECK:STDOUT:
+// CHECK:STDOUT: declare void @_CG.Main(ptr)
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nounwind
+// CHECK:STDOUT: define void @_CF.Main() #0 !dbg !4 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %insert_padding.var = alloca <{ <{ { i32, i32, i32 }, [4 x i8] }>, ptr, i32 }>, align 8, !dbg !7
+// CHECK:STDOUT:   call void @llvm.lifetime.start.p0(ptr %insert_padding.var), !dbg !7
+// CHECK:STDOUT:   %.loc10.b = getelementptr inbounds nuw <{ <{ { i32, i32, i32 }, [4 x i8] }>, ptr, i32 }>, ptr %insert_padding.var, i32 0, i32 1, !dbg !8
+// CHECK:STDOUT:   call void @_CG.Main(ptr %.loc10.b), !dbg !9
+// CHECK:STDOUT:   call void @"_COp.ad98736f0dc6e810:core.Destroy.Core"(ptr %insert_padding.var), !dbg !7
+// CHECK:STDOUT:   ret void, !dbg !10
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nounwind
+// CHECK:STDOUT: define weak_odr void @"_COp.7e389eab4a7e5487:core.Destroy.Core"(ptr %self) #0 !dbg !11 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   ret void, !dbg !17
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nounwind
+// CHECK:STDOUT: define weak_odr void @"_COp.3124a28397dbe9e9:core.Destroy.Core"(ptr %self) #0 !dbg !18 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   ret void, !dbg !24
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nounwind
+// CHECK:STDOUT: define weak_odr void @"_COp.ad98736f0dc6e810:core.Destroy.Core"(ptr %self) #0 !dbg !25 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   ret void, !dbg !28
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nocallback nofree nosync nounwind willreturn memory(argmem: readwrite)
+// CHECK:STDOUT: declare void @llvm.lifetime.start.p0(ptr captures(none)) #1
+// CHECK:STDOUT:
+// CHECK:STDOUT: attributes #0 = { nounwind }
+// CHECK:STDOUT: attributes #1 = { nocallback nofree nosync nounwind willreturn memory(argmem: readwrite) }
+// CHECK:STDOUT:
+// CHECK:STDOUT: !llvm.module.flags = !{!0, !1}
+// CHECK:STDOUT: !llvm.dbg.cu = !{!2}
+// CHECK:STDOUT:
+// CHECK:STDOUT: !0 = !{i32 7, !"Dwarf Version", i32 5}
+// CHECK:STDOUT: !1 = !{i32 2, !"Debug Info Version", i32 3}
+// CHECK:STDOUT: !2 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !3, producer: "carbon", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug)
+// CHECK:STDOUT: !3 = !DIFile(filename: "insert_padding.carbon", directory: "")
+// CHECK:STDOUT: !4 = distinct !DISubprogram(name: "F", linkageName: "_CF.Main", scope: null, file: !3, line: 5, type: !5, spFlags: DISPFlagDefinition, unit: !2)
+// CHECK:STDOUT: !5 = !DISubroutineType(types: !6)
+// CHECK:STDOUT: !6 = !{null}
+// CHECK:STDOUT: !7 = !DILocation(line: 9, column: 3, scope: !4)
+// CHECK:STDOUT: !8 = !DILocation(line: 10, column: 6, scope: !4)
+// CHECK:STDOUT: !9 = !DILocation(line: 10, column: 3, scope: !4)
+// CHECK:STDOUT: !10 = !DILocation(line: 5, column: 1, scope: !4)
+// CHECK:STDOUT: !11 = distinct !DISubprogram(name: "Op", linkageName: "_COp.7e389eab4a7e5487:core.Destroy.Core", scope: null, file: !3, line: 9, type: !12, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !15)
+// CHECK:STDOUT: !12 = !DISubroutineType(types: !13)
+// CHECK:STDOUT: !13 = !{null, !14}
+// CHECK:STDOUT: !14 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+// CHECK:STDOUT: !15 = !{!16}
+// CHECK:STDOUT: !16 = !DILocalVariable(arg: 1, scope: !11, type: !14)
+// CHECK:STDOUT: !17 = !DILocation(line: 9, column: 3, scope: !11)
+// CHECK:STDOUT: !18 = distinct !DISubprogram(name: "Op", linkageName: "_COp.3124a28397dbe9e9:core.Destroy.Core", scope: null, file: !3, line: 9, type: !19, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !22)
+// CHECK:STDOUT: !19 = !DISubroutineType(types: !20)
+// CHECK:STDOUT: !20 = !{null, !21}
+// CHECK:STDOUT: !21 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: null, size: 64)
+// CHECK:STDOUT: !22 = !{!23}
+// CHECK:STDOUT: !23 = !DILocalVariable(arg: 1, scope: !18, type: !21)
+// CHECK:STDOUT: !24 = !DILocation(line: 9, column: 3, scope: !18)
+// CHECK:STDOUT: !25 = distinct !DISubprogram(name: "Op", linkageName: "_COp.ad98736f0dc6e810:core.Destroy.Core", scope: null, file: !3, line: 9, type: !19, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !26)
+// CHECK:STDOUT: !26 = !{!27}
+// CHECK:STDOUT: !27 = !DILocalVariable(arg: 1, scope: !25, type: !21)
+// CHECK:STDOUT: !28 = !DILocation(line: 9, column: 3, scope: !25)
diff --git a/toolchain/lower/testdata/struct/member_access.carbon b/toolchain/lower/testdata/struct/member_access.carbon
index 567dd89552ac..2562f739d0eb 100644
--- a/toolchain/lower/testdata/struct/member_access.carbon
+++ b/toolchain/lower/testdata/struct/member_access.carbon
@@ -20,20 +20,20 @@ fn Run() -> i32 {
 // CHECK:STDOUT: ; ModuleID = 'member_access.carbon'
 // CHECK:STDOUT: source_filename = "member_access.carbon"
 // CHECK:STDOUT:
-// CHECK:STDOUT: @struct.454.loc14_3 = internal constant { double, i32 } { double 0.000000e+00, i32 1 }
+// CHECK:STDOUT: @struct.454.loc14_3 = internal constant <{ double, i32 }> <{ double 0.000000e+00, i32 1 }>
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
 // CHECK:STDOUT: define i32 @main() #0 !dbg !4 {
 // CHECK:STDOUT: entry:
-// CHECK:STDOUT:   %x.var = alloca { double, i32 }, align 8, !dbg !8
+// CHECK:STDOUT:   %x.var = alloca <{ double, i32 }>, align 8, !dbg !8
 // CHECK:STDOUT:   %y.var = alloca i32, align 4, !dbg !9
 // CHECK:STDOUT:   %_.var = alloca i32, align 4, !dbg !10
 // CHECK:STDOUT:   call void @llvm.lifetime.start.p0(ptr %x.var), !dbg !8
-// CHECK:STDOUT:   %.loc14_48.3.a = getelementptr inbounds nuw { double, i32 }, ptr %x.var, i32 0, i32 0, !dbg !11
-// CHECK:STDOUT:   %.loc14_48.6.b = getelementptr inbounds nuw { double, i32 }, ptr %x.var, i32 0, i32 1, !dbg !11
-// CHECK:STDOUT:   call void @llvm.memcpy.p0.p0.i64(ptr align 8 %x.var, ptr align 8 @struct.454.loc14_3, i64 16, i1 false), !dbg !8
+// CHECK:STDOUT:   %.loc14_48.3.a = getelementptr inbounds nuw <{ double, i32 }>, ptr %x.var, i32 0, i32 0, !dbg !11
+// CHECK:STDOUT:   %.loc14_48.6.b = getelementptr inbounds nuw <{ double, i32 }>, ptr %x.var, i32 0, i32 1, !dbg !11
+// CHECK:STDOUT:   call void @llvm.memcpy.p0.p0.i64(ptr align 1 %x.var, ptr align 1 @struct.454.loc14_3, i64 12, i1 false), !dbg !8
 // CHECK:STDOUT:   call void @llvm.lifetime.start.p0(ptr %y.var), !dbg !9
-// CHECK:STDOUT:   %.loc15_17.1.b = getelementptr inbounds nuw { double, i32 }, ptr %x.var, i32 0, i32 1, !dbg !12
+// CHECK:STDOUT:   %.loc15_17.1.b = getelementptr inbounds nuw <{ double, i32 }>, ptr %x.var, i32 0, i32 1, !dbg !12
 // CHECK:STDOUT:   %.loc15_17.2 = load i32, ptr %.loc15_17.1.b, align 4, !dbg !12
 // CHECK:STDOUT:   store i32 %.loc15_17.2, ptr %y.var, align 4, !dbg !9
 // CHECK:STDOUT:   call void @llvm.lifetime.start.p0(ptr %_.var), !dbg !10
diff --git a/toolchain/sem_ir/file.cpp b/toolchain/sem_ir/file.cpp
index e186507ceb98..e431bb23c49d 100644
--- a/toolchain/sem_ir/file.cpp
+++ b/toolchain/sem_ir/file.cpp
@@ -70,15 +70,20 @@ File::File(const Parse::Tree* parse_tree, CheckIRId check_ir_id,
       expr_regions_(check_ir_id),
       clang_source_locs_(check_ir_id) {
   // `type`, `form`, and the error type are both complete & concrete types.
+  // TODO: This duplicates the code in `check/type_completion.cpp`. Consider
+  // requiring these types to be complete from Check initialization instead.
   types_.SetComplete(
       TypeType::TypeId,
-      {.value_repr = {.kind = ValueRepr::Copy, .type_id = TypeType::TypeId}});
+      {.value_repr = {.kind = ValueRepr::Copy, .type_id = TypeType::TypeId},
+       .object_layout = SemIR::ObjectLayout::Empty()});
   types_.SetComplete(
       FormType::TypeId,
-      {.value_repr = {.kind = ValueRepr::Copy, .type_id = FormType::TypeId}});
+      {.value_repr = {.kind = ValueRepr::Copy, .type_id = FormType::TypeId},
+       .object_layout = SemIR::ObjectLayout::Empty()});
   types_.SetComplete(
       ErrorInst::TypeId,
-      {.value_repr = {.kind = ValueRepr::Copy, .type_id = ErrorInst::TypeId}});
+      {.value_repr = {.kind = ValueRepr::Copy, .type_id = ErrorInst::TypeId},
+       .object_layout = SemIR::ObjectLayout::Empty()});
 
   insts_.Reserve(SingletonInstKinds.size());
   for (auto kind : SingletonInstKinds) {
diff --git a/toolchain/sem_ir/file.h b/toolchain/sem_ir/file.h
index 003e5362b178..5f0022c6147c 100644
--- a/toolchain/sem_ir/file.h
+++ b/toolchain/sem_ir/file.h
@@ -66,7 +66,7 @@ struct ExprRegion {
 using ExprRegionStore = ValueStore<ExprRegionId, ExprRegion, Tag<CheckIRId>>;
 
 using CustomLayoutStore =
-    BlockValueStore<CustomLayoutId, uint64_t, Tag<CheckIRId>>;
+    BlockValueStore<CustomLayoutId, ObjectSize, Tag<CheckIRId>>;
 
 // The semantic IR for a single file.
 class File : public Printable<File> {
@@ -95,16 +95,23 @@ class File : public Printable<File> {
   auto CollectMemUsage(MemUsage& mem_usage, llvm::StringRef label) const
       -> void;
 
-  // Returns array bound value from the bound instruction.
+  // Returns the zero-extended integer value of the given instruction if it is a
+  // constant integer.
   // TODO: Move this function elsewhere.
-  auto GetArrayBoundValue(InstId bound_id) const -> std::optional<uint64_t> {
-    if (auto bound = insts().TryGetAs<IntValue>(
-            constant_values().GetConstantInstId(bound_id))) {
-      return ints().Get(bound->int_id).getZExtValue();
+  auto GetZExtIntValue(InstId inst_id) const -> std::optional<uint64_t> {
+    if (auto val = insts().TryGetAs<IntValue>(
+            constant_values().GetConstantInstId(inst_id))) {
+      return ints().Get(val->int_id).getZExtValue();
     }
     return std::nullopt;
   }
 
+  // Returns the layout of a pointer.
+  // TODO: This should depend on the target machine.
+  auto GetPointerLayout() const -> ObjectLayout {
+    return {.size = ObjectSize::Bytes(8), .alignment = ObjectSize::Bytes(8)};
+  }
+
   // Gets the pointee type of the given type, which must be a pointer type.
   // TODO: Move this function elsewhere.
   auto GetPointeeType(TypeId pointer_id) const -> TypeId {
diff --git a/toolchain/sem_ir/inst_fingerprinter.cpp b/toolchain/sem_ir/inst_fingerprinter.cpp
index 197ac044a0a2..4c9f604ecdd8 100644
--- a/toolchain/sem_ir/inst_fingerprinter.cpp
+++ b/toolchain/sem_ir/inst_fingerprinter.cpp
@@ -191,7 +191,9 @@ struct Worklist {
     }
     auto block = sem_ir->custom_layouts().Get(custom_layout_id);
     contents.push_back(block.size());
-    contents.insert(contents.end(), block.begin(), block.end());
+    for (auto size : block) {
+      contents.push_back(size.bits());
+    }
   }
 
   auto Add(NameScopeId name_scope_id) -> void {
diff --git a/toolchain/sem_ir/type.h b/toolchain/sem_ir/type.h
index be241143a540..6aa3b20961a7 100644
--- a/toolchain/sem_ir/type.h
+++ b/toolchain/sem_ir/type.h
@@ -249,6 +249,15 @@ class TypeStore : public Yaml::Printable<TypeStore> {
         map.Add(PrintToString(type_id),
                 Yaml::OutputMapping([&](Yaml::OutputMapping::Map map2) {
                   map2.Add("value_repr", Yaml::OutputScalar(info.value_repr));
+                  map2.Add(
+                      "object_layout",
+                      Yaml::OutputMapping([&](Yaml::OutputMapping::Map map3) {
+                        map3.Add("size",
+                                 Yaml::OutputScalar(info.object_layout.size));
+                        map3.Add(
+                            "alignment",
+                            Yaml::OutputScalar(info.object_layout.alignment));
+                      }));
                   if (info.abstract_class_id.has_value()) {
                     map2.Add("abstract_class_id",
                              Yaml::OutputScalar(info.abstract_class_id));
diff --git a/toolchain/sem_ir/type_info.cpp b/toolchain/sem_ir/type_info.cpp
index 25f8e2e8dd77..fedceb28a523 100644
--- a/toolchain/sem_ir/type_info.cpp
+++ b/toolchain/sem_ir/type_info.cpp
@@ -37,7 +37,18 @@ auto ValueRepr::Print(llvm::raw_ostream& out) const -> void {
 }
 
 auto CompleteTypeInfo::Print(llvm::raw_ostream& out) const -> void {
-  out << "{value_rep: " << value_repr << "}";
+  out << "{value_rep: " << value_repr
+      << ", layout: {size: " << object_layout.size
+      << ", align: " << object_layout.alignment << "}}";
+}
+
+auto ObjectSize::Print(llvm::raw_ostream& out) const -> void {
+  int64_t bytes = bits_ / 8;
+  int64_t bits = bits_ % 8;
+  out << bytes;
+  if (bits != 0) {
+    out << ":" << bits;
+  }
 }
 
 auto ValueRepr::ForType(const File& file, TypeId type_id) -> ValueRepr {
diff --git a/toolchain/sem_ir/type_info.h b/toolchain/sem_ir/type_info.h
index 9a899633337e..a77a7cef0cbb 100644
--- a/toolchain/sem_ir/type_info.h
+++ b/toolchain/sem_ir/type_info.h
@@ -73,6 +73,146 @@ struct ValueRepr : public Printable<ValueRepr> {
   TypeId type_id = TypeId::None;
 };
 
+// A size within an object representation. This stores a bit count, but provides
+// convenience methods to access the size in bytes instead.
+class ObjectSize : public Printable<ObjectSize> {
+ public:
+  static constexpr auto Zero() -> ObjectSize { return ObjectSize(0); }
+
+  static constexpr auto Bits(int64_t bits) -> ObjectSize {
+    return ObjectSize(bits);
+  }
+
+  static constexpr auto Bytes(int64_t bytes) -> ObjectSize {
+    return ObjectSize(bytes * 8);
+  }
+
+  // Returns the size in bits.
+  auto bits() const -> int64_t { return bits_; }
+
+  // Returns the minimum number of bytes that would contain this size. This is
+  // the size in bytes, rounded up.
+  auto bytes() const -> int64_t { return (bits_ + 7) / 8; }
+
+  // Return this size rounded up to a multiple of `align`, which must be a power
+  // of 2.
+  [[nodiscard]] auto AlignedTo(ObjectSize align) const -> ObjectSize {
+    CARBON_CHECK(llvm::isPowerOf2_64(align.bits_),
+                 "Non power-of-2 alignment {0}", align.bits_);
+    return Bits((bits_ + align.bits_ - 1) & -align.bits_);
+  }
+
+  auto Print(llvm::raw_ostream& out) const -> void;
+
+  friend constexpr auto operator<=>(ObjectSize a, ObjectSize b) {
+    return a.bits_ <=> b.bits_;
+  }
+
+  friend constexpr auto operator==(ObjectSize a, ObjectSize b) -> bool {
+    return a.bits_ == b.bits_;
+  }
+
+  // Computes the sum of two object sizes. This is the size of the smallest
+  // object that could fit both objects consecutively, without any alignment
+  // constraints or other padding bits.
+  auto operator+=(ObjectSize other) -> ObjectSize& {
+    bits_ += other.bits_;
+    return *this;
+  }
+  friend auto operator+(ObjectSize a, ObjectSize b) -> ObjectSize {
+    return a += b;
+  }
+
+  // Scales a size by a dimensionless integer. This is the size of `n` objects
+  // of the given size, laid out contiguously with no padding between them.
+  // Equivalent to adding the size to itself `n` times.
+  auto operator*=(int64_t n) -> ObjectSize& {
+    CARBON_CHECK(n >= 0, "sizes should not be negative");
+    bits_ *= n;
+    return *this;
+  }
+  friend auto operator*(ObjectSize a, int64_t n) -> ObjectSize {
+    return a *= n;
+  }
+  friend auto operator*(int64_t n, ObjectSize a) -> ObjectSize {
+    return a *= n;
+  }
+
+ private:
+  explicit constexpr ObjectSize(int64_t bits) : bits_(bits) {
+    CARBON_CHECK(bits >= 0, "sizes should not be negative");
+  }
+
+  int64_t bits_;
+};
+
+// The layout of an object representation.
+struct ObjectLayout {
+  // The size of the object representation. This may be zero for empty types.
+  // This is not guaranteed to be a multiple of `alignment`, so explicit tail
+  // padding may be required if objects using this layout are stored in an
+  // array.
+  ObjectSize size = ObjectSize::Zero();
+
+  // The alignment of the object representation. This will be a power of 2 for a
+  // valid representation, or zero if the representation is unset (such as for
+  // the object layout of an incomplete type). This will typically be 1 byte for
+  // an empty type.
+  ObjectSize alignment = ObjectSize::Zero();
+
+  // Returns the object layout to use for an empty type.
+  [[nodiscard]] static auto Empty() -> ObjectLayout {
+    return {.size = ObjectSize::Zero(), .alignment = ObjectSize::Bytes(1)};
+  }
+
+  // Returns the object layout to use for an array of `count` elements. The
+  // result never has tail padding, so this is *not* the same as adding the
+  // element to itself `count` times in general.
+  static auto ForArray(ObjectLayout element_layout, int64_t count)
+      -> ObjectLayout {
+    return {.size = element_layout.ArrayStride() * count,
+            .alignment = element_layout.alignment};
+  }
+
+  // Returns the stride of an array with this element type.
+  auto ArrayStride() const -> ObjectSize { return size.AlignedTo(alignment); }
+
+  // Returns the offset that a field with the given layout would have if
+  // appended to this struct.
+  auto FieldOffset(ObjectLayout field) -> ObjectSize {
+    CARBON_CHECK(field.has_value());
+    return size.AlignedTo(field.alignment);
+  }
+
+  // Updates this aggregate layout by concatenating naturally-aligned space for
+  // the given field layout, which is required to be valid.
+  auto AppendField(ObjectLayout field) -> void {
+    size = FieldOffset(field) + field.size;
+    alignment = std::max(alignment, field.alignment);
+  }
+
+  // Updates this aggregate layout by concatenating naturally-aligned space for
+  // the given field layout, if the field has a valid layout. If any field with
+  // an invalid layout is appended, the layout of the aggregate becomes invalid.
+  //
+  // An invalid layout for a field with a complete type indicates that its
+  // layout is dependent on a generic parameter; this causes the layout of the
+  // enclosing aggregate to also be dependent on that parameter.
+  auto TryAppendField(ObjectLayout field) -> void {
+    if (has_value()) {
+      if (field.has_value()) {
+        AppendField(field);
+      } else {
+        *this = ObjectLayout();
+      }
+    }
+  }
+
+  // Returns true if the layout has been set. For a complete type, this will be
+  // true if the layout is non-dependent.
+  auto has_value() const -> bool { return alignment != ObjectSize::Zero(); }
+};
+
 // Information stored about a TypeId corresponding to a complete type.
 struct CompleteTypeInfo : public Printable<CompleteTypeInfo> {
   auto Print(llvm::raw_ostream& out) const -> void;
@@ -81,6 +221,10 @@ struct CompleteTypeInfo : public Printable<CompleteTypeInfo> {
   // not complete.
   ValueRepr value_repr = ValueRepr();
 
+  // The layout of the object representation of this type. This will be valid
+  // unless the type is incomplete or dependent.
+  ObjectLayout object_layout = ObjectLayout();
+
   // If this type is abstract, this is id of an abstract class it uses.
   ClassId abstract_class_id = ClassId::None;