diff --git a/toolchain/check/check.cpp b/toolchain/check/check.cpp
index b62ceb5ee2e4..899ae21eb7b9 100644
--- a/toolchain/check/check.cpp
+++ b/toolchain/check/check.cpp
@@ -507,14 +507,23 @@ auto CheckParseTrees(
 
   // Create C++ domains for Cpp imports.
   if (options.share_cpp_ast) {
+    llvm::SmallVector<CppInputFile> inputs;
+    for (auto& unit_info : unit_infos) {
+      if (unit_info.cpp_imports.empty()) {
+        continue;
+      }
+      inputs.push_back({.check_ir_id = unit_info.unit->sem_ir->check_ir_id(),
+                        .filename = unit_info.unit->sem_ir->filename()});
+    }
     // TODO: Remove dependence on properties of the first unit here.
     if (auto cpp_domain = InitializeCppDomain(
-            unit_infos.front().err_tracker,
-            unit_infos.front().unit->sem_ir->filename(), fs,
+            unit_infos.front().err_tracker, inputs, fs,
             unit_infos.front().unit->llvm_context, clang_invocation)) {
       cpp_domains.push_back(std::move(cpp_domain));
-      for (auto& target_info : unit_infos) {
-        target_info.cpp_domain = cpp_domains.back().get();
+      for (auto& unit_info : unit_infos) {
+        if (!unit_info.cpp_imports.empty()) {
+          unit_info.cpp_domain = cpp_domains.back().get();
+        }
       }
     }
   } else {
@@ -523,8 +532,10 @@ auto CheckParseTrees(
         continue;
       }
       if (auto cpp_domain = InitializeCppDomain(
-              unit_info.err_tracker, unit_info.unit->sem_ir->filename(), fs,
-              unit_info.unit->llvm_context, clang_invocation)) {
+              unit_info.err_tracker,
+              {{.check_ir_id = unit_info.unit->sem_ir->check_ir_id(),
+                .filename = unit_info.unit->sem_ir->filename()}},
+              fs, unit_info.unit->llvm_context, clang_invocation)) {
         cpp_domains.push_back(std::move(cpp_domain));
         unit_info.cpp_domain = cpp_domains.back().get();
       }
diff --git a/toolchain/check/cpp/domain.cpp b/toolchain/check/cpp/domain.cpp
index 68a0f939fda3..527c7328706a 100644
--- a/toolchain/check/cpp/domain.cpp
+++ b/toolchain/check/cpp/domain.cpp
@@ -10,12 +10,20 @@ namespace Carbon::Check {
 
 CppDomain::CppDomain(std::shared_ptr<clang::CompilerInstance> clang_instance,
                      std::unique_ptr<clang::Parser> parser,
-                     clang::CodeGenerator* code_generator,
+                     llvm::ArrayRef<CppInputFile> inputs,
+                     llvm::ArrayRef<clang::CodeGenerator*> code_generators,
                      llvm::LLVMContext* llvm_context)
     : clang_instance_(std::move(clang_instance)),
       parser_(std::move(parser)),
-      code_generator_(code_generator),
-      llvm_context_(llvm_context) {}
+      llvm_context_(llvm_context) {
+  CARBON_CHECK(inputs.size() == code_generators.size());
+  for (size_t i = 0; i < inputs.size(); ++i) {
+    auto res =
+        code_generators_.Insert(inputs[i].check_ir_id, code_generators[i]);
+    CARBON_CHECK(res.is_inserted(), "Duplicate CheckIRId {0} in CppDomain",
+                 inputs[i].check_ir_id);
+  }
+}
 
 CppDomain::~CppDomain() = default;
 
diff --git a/toolchain/check/cpp/domain.h b/toolchain/check/cpp/domain.h
index 8f08be69125e..1b586f7e4565 100644
--- a/toolchain/check/cpp/domain.h
+++ b/toolchain/check/cpp/domain.h
@@ -7,6 +7,11 @@
 
 #include <memory>
 
+#include "common/check.h"
+#include "common/map.h"
+#include "llvm/ADT/ArrayRef.h"
+#include "toolchain/sem_ir/ids.h"
+
 namespace clang {
 class CodeGenerator;
 class CompilerInstance;
@@ -19,13 +24,20 @@ class LLVMContext;
 
 namespace Carbon::Check {
 
+// An input Carbon file and its CheckIRId for C++ domain code generation.
+struct CppInputFile {
+  SemIR::CheckIRId check_ir_id;
+  llvm::StringRef filename;
+};
+
 // A C++ compilation domain, including a live Clang instance that can be used to
 // parse more code into that domain. May be shared across multiple Carbon files.
 class CppDomain {
  public:
   explicit CppDomain(std::shared_ptr<clang::CompilerInstance> clang_instance,
                      std::unique_ptr<clang::Parser> parser,
-                     clang::CodeGenerator* code_generator,
+                     llvm::ArrayRef<CppInputFile> inputs,
+                     llvm::ArrayRef<clang::CodeGenerator*> code_generators,
                      llvm::LLVMContext* llvm_context);
   ~CppDomain();
 
@@ -36,15 +48,19 @@ class CppDomain {
     return clang_instance_;
   }
   auto parser() const -> clang::Parser& { return *parser_; }
-  auto code_generator() const -> clang::CodeGenerator* {
-    return code_generator_;
-  }
   auto llvm_context() const -> llvm::LLVMContext* { return llvm_context_; }
 
+  auto GetCodeGenerator(SemIR::CheckIRId check_ir_id) const
+      -> clang::CodeGenerator* {
+    auto res = code_generators_.Lookup(check_ir_id);
+    CARBON_CHECK(res, "No CodeGenerator found for CheckIRId {0}", check_ir_id);
+    return res.value();
+  }
+
  private:
   std::shared_ptr<clang::CompilerInstance> clang_instance_;
   std::unique_ptr<clang::Parser> parser_;
-  clang::CodeGenerator* code_generator_ = nullptr;
+  Map<SemIR::CheckIRId, clang::CodeGenerator*> code_generators_;
   llvm::LLVMContext* llvm_context_ = nullptr;
 };
 
diff --git a/toolchain/check/cpp/generate_ast.cpp b/toolchain/check/cpp/generate_ast.cpp
index 36780e94e290..e46a03b2eb00 100644
--- a/toolchain/check/cpp/generate_ast.cpp
+++ b/toolchain/check/cpp/generate_ast.cpp
@@ -9,12 +9,14 @@
 
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/Decl.h"
+#include "clang/AST/Mangle.h"
 #include "clang/Basic/DiagnosticParse.h"
 #include "clang/Basic/FileManager.h"
 #include "clang/CodeGen/ModuleBuilder.h"
 #include "clang/Frontend/CompilerInstance.h"
 #include "clang/Frontend/CompilerInvocation.h"
 #include "clang/Frontend/FrontendAction.h"
+#include "clang/Frontend/MultiplexConsumer.h"
 #include "clang/Frontend/TextDiagnostic.h"
 #include "clang/Lex/PreprocessorOptions.h"
 #include "clang/Parse/Parser.h"
@@ -714,12 +716,12 @@ namespace {
 // from a set of Cpp imports.
 class GenerateASTAction : public clang::ASTFrontendAction {
  public:
-  explicit GenerateASTAction(llvm::StringRef filename,
+  explicit GenerateASTAction(llvm::ArrayRef<CppInputFile> inputs,
                              llvm::LLVMContext* llvm_context)
-      : filename_(filename), llvm_context_(llvm_context) {}
+      : inputs_(inputs), llvm_context_(llvm_context) {}
 
-  auto code_generator() const -> clang::CodeGenerator* {
-    return code_generator_;
+  auto code_generators() const -> llvm::ArrayRef<clang::CodeGenerator*> {
+    return code_generators_;
   }
 
   auto TakeParser() -> std::unique_ptr<clang::Parser> {
@@ -733,15 +735,28 @@ class GenerateASTAction : public clang::ASTFrontendAction {
     if (!llvm_context_) {
       return std::make_unique<clang::ASTConsumer>();
     }
-    auto code_generator =
-        std::unique_ptr<clang::CodeGenerator>(clang::CreateLLVMCodeGen(
-            clang_instance.getDiagnostics(), filename_,
-            clang_instance.getVirtualFileSystemPtr(),
-            clang_instance.getHeaderSearchOpts(),
-            clang_instance.getPreprocessorOpts(),
-            clang_instance.getCodeGenOpts(), *llvm_context_));
-    code_generator_ = code_generator.get();
-    return code_generator;
+    // Build a code generator for each object file we will be building. For now
+    // we assume that we want one object file per Carbon source file.
+    // TODO: Only build CodeGenerators for the files we're actually generating
+    // code for.
+    // TODO: Consider supporting generating code for multiple Carbon files into
+    // a single object file, for a faster `carbon build` mode.
+    std::vector<std::unique_ptr<clang::ASTConsumer>> consumers;
+    for (const auto& input : inputs_) {
+      // TODO: Filter what goes into each code generator. If there are strong
+      // external C++ definitions in a Carbon file (for example, in inline C++
+      // code), they should be emitted only in that one file.
+      auto code_generator =
+          std::unique_ptr<clang::CodeGenerator>(clang::CreateLLVMCodeGen(
+              clang_instance.getDiagnostics(), input.filename,
+              clang_instance.getVirtualFileSystemPtr(),
+              clang_instance.getHeaderSearchOpts(),
+              clang_instance.getPreprocessorOpts(),
+              clang_instance.getCodeGenOpts(), *llvm_context_));
+      code_generators_.push_back(code_generator.get());
+      consumers.push_back(std::move(code_generator));
+    }
+    return std::make_unique<clang::MultiplexConsumer>(std::move(consumers));
   }
 
   auto BeginSourceFileAction(clang::CompilerInstance& /*clang_instance*/)
@@ -776,9 +791,9 @@ class GenerateASTAction : public clang::ASTFrontendAction {
   }
 
  private:
-  std::string filename_;
+  llvm::ArrayRef<CppInputFile> inputs_;
   llvm::LLVMContext* llvm_context_;
-  clang::CodeGenerator* code_generator_ = nullptr;
+  llvm::SmallVector<clang::CodeGenerator*> code_generators_;
   std::unique_ptr<clang::Parser> parser_;
 };
 
@@ -788,7 +803,7 @@ class GenerateASTAction : public clang::ASTFrontendAction {
 // creating a diagnostics engine, and parsing a dummy main file containing a
 // semicolon. Returns the initialized state, or null on failure.
 auto InitializeCppDomain(
-    Diagnostics::Consumer& consumer, llvm::StringRef filename,
+    Diagnostics::Consumer& consumer, llvm::ArrayRef<CppInputFile> inputs,
     llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> fs,
     llvm::LLVMContext* llvm_context,
     std::shared_ptr<clang::CompilerInvocation> base_invocation)
@@ -816,11 +831,12 @@ auto InitializeCppDomain(
 
   // Extract the input from the frontend invocation and make sure it makes
   // sense.
-  const auto& inputs = invocation->getFrontendOpts().Inputs;
-  CARBON_CHECK(inputs.size() == 1 &&
-               inputs[0].getKind().getLanguage() == clang::Language::CXX &&
-               inputs[0].getKind().getFormat() == clang::InputKind::Source);
-  llvm::StringRef file_name = inputs[0].getFile();
+  const auto& clang_inputs = invocation->getFrontendOpts().Inputs;
+  CARBON_CHECK(clang_inputs.size() == 1);
+  CARBON_CHECK(clang_inputs[0].getKind().getLanguage() == clang::Language::CXX);
+  CARBON_CHECK(clang_inputs[0].getKind().getFormat() ==
+               clang::InputKind::Source);
+  llvm::StringRef file_name = clang_inputs[0].getFile();
 
   // Remap the input file to a dummy buffer containing a semicolon to start
   // with an empty AST. Clang requires at least one token in the main file
@@ -841,8 +857,8 @@ auto InitializeCppDomain(
     return nullptr;
   }
 
-  GenerateASTAction action(filename, llvm_context);
-  if (!action.BeginSourceFile(*clang_instance, inputs[0])) {
+  GenerateASTAction action(inputs, llvm_context);
+  if (!action.BeginSourceFile(*clang_instance, clang_inputs[0])) {
     return nullptr;
   }
 
@@ -880,9 +896,10 @@ auto InitializeCppDomain(
   auto parser = action.TakeParser();
   CARBON_CHECK(parser);
 
+  CARBON_CHECK(action.code_generators().size() == inputs.size());
   return std::make_unique<CppDomain>(std::move(clang_instance),
-                                     std::move(parser), action.code_generator(),
-                                     llvm_context);
+                                     std::move(parser), inputs,
+                                     action.code_generators(), llvm_context);
 }
 
 auto GenerateAst(Context& context,
@@ -900,23 +917,19 @@ auto GenerateAst(Context& context,
 
   auto clang_instance = domain.clang_instance_ptr();
 
+  auto mangle_context = std::unique_ptr<clang::MangleContext>(
+      clang_instance->getASTContext().createMangleContext());
+
   // Set up CppFile for the current SemIR::File.
-  auto cpp_file =
-      std::make_unique<SemIR::CppFile>(clang_instance, domain.llvm_context());
-  if (domain.code_generator()) {
-    cpp_file->SetCodeGenerator(domain.code_generator());
-  }
-  context.sem_ir().set_cpp_file(std::move(cpp_file));
+  context.sem_ir().set_cpp_file(std::make_unique<SemIR::CppFile>(
+      clang_instance, std::move(mangle_context), domain.llvm_context(),
+      domain.GetCodeGenerator(context.sem_ir().check_ir_id())));
 
   // Set up CppContext for the current Context.
   context.set_cpp_context(std::make_unique<CppContext>(
       domain, MakeContextDiagnosticListener(
                   *clang_instance->getDiagnostics().getClient(), context)));
 
-  // The AST context is now available, so the mangle context (used to compute
-  // stable identities for imported C++ types) can be created.
-  context.sem_ir().cpp_file()->CreateMangleContext();
-
   // Add an external source referring to this context.
   auto* multiplex_source = cast<clang::MultiplexExternalSemaSource>(
       context.ast_context().getExternalSource());
diff --git a/toolchain/check/cpp/generate_ast.h b/toolchain/check/cpp/generate_ast.h
index 0a6794527be6..733c8eddba06 100644
--- a/toolchain/check/cpp/generate_ast.h
+++ b/toolchain/check/cpp/generate_ast.h
@@ -12,6 +12,7 @@
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/VirtualFileSystem.h"
 #include "toolchain/check/context.h"
+#include "toolchain/check/cpp/domain.h"
 #include "toolchain/parse/tree.h"
 #include "toolchain/sem_ir/ids.h"
 
@@ -35,7 +36,7 @@ class CppDomain;
 // within one or more Carbon files. Returns the initialized state, or null on
 // failure.
 auto InitializeCppDomain(
-    Diagnostics::Consumer& consumer, llvm::StringRef filename,
+    Diagnostics::Consumer& consumer, llvm::ArrayRef<CppInputFile> inputs,
     llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> fs,
     llvm::LLVMContext* llvm_context,
     std::shared_ptr<clang::CompilerInvocation> base_invocation)
diff --git a/toolchain/check/testdata/interop/cpp/basics/share_ast.carbon b/toolchain/check/testdata/interop/cpp/basics/share_ast.carbon
index d3efea075c01..3546bc8f8daa 100644
--- a/toolchain/check/testdata/interop/cpp/basics/share_ast.carbon
+++ b/toolchain/check/testdata/interop/cpp/basics/share_ast.carbon
@@ -2,9 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// ARGS: compile --phase=check --share-cpp-ast %s
-//
 // INCLUDE-FILE: toolchain/testing/testdata/min_prelude/int.carbon
+// EXTRA-ARGS: --share-cpp-ast
 //
 // AUTOUPDATE
 // TIP: To test this file alone, run:
@@ -39,7 +38,7 @@ import Cpp;
 
 fn CallLeakedA() -> i32 {
   // This should not be found as we have not imported "a.h".
-  // CHECK:STDERR: fail_a_does_not_leak.carbon:[[@LINE+4]]:10: error: member name `GetA` not found in `Cpp`
+  // CHECK:STDERR: fail_a_does_not_leak.carbon:[[@LINE+4]]:10: error: member name `GetA` not found in `Cpp` [MemberNameNotFoundInInstScope]
   // CHECK:STDERR:   return Cpp.GetA();
   // CHECK:STDERR:          ^~~~~~~~
   // CHECK:STDERR:
diff --git a/toolchain/driver/compile_driver.cpp b/toolchain/driver/compile_driver.cpp
index 506ff42d8c18..a5f1d3ce3981 100644
--- a/toolchain/driver/compile_driver.cpp
+++ b/toolchain/driver/compile_driver.cpp
@@ -40,13 +40,11 @@
 
 namespace Carbon {
 
-CompilationUnit::CompilationUnit(SemIR::CheckIRId check_ir_id,
-                                 int total_ir_count, DriverEnv* driver_env,
-                                 const CompileOptions* options,
-                                 Diagnostics::Consumer* consumer,
-                                 llvm::StringRef input_filename,
-                                 std::string output_filename,
-                                 const llvm::Target* target)
+CompilationUnit::CompilationUnit(
+    SemIR::CheckIRId check_ir_id, int total_ir_count, DriverEnv* driver_env,
+    const CompileOptions* options, Diagnostics::Consumer* consumer,
+    llvm::StringRef input_filename, std::string output_filename,
+    const llvm::Target* target, llvm::LLVMContext* llvm_context)
     : check_ir_id_(check_ir_id),
       total_ir_count_(total_ir_count),
       driver_env_(driver_env),
@@ -54,7 +52,8 @@ CompilationUnit::CompilationUnit(SemIR::CheckIRId check_ir_id,
       target_(target),
       input_filename_(input_filename),
       output_filename_(std::move(output_filename)),
-      vlog_stream_(driver_env_->vlog_stream) {
+      vlog_stream_(driver_env_->vlog_stream),
+      llvm_context_(llvm_context) {
   if (vlog_stream_ != nullptr || options_->stream_errors) {
     consumer_ = consumer;
   } else {
@@ -150,14 +149,11 @@ auto CompilationUnit::GetCheckUnit() -> Check::Unit {
   };
   sem_ir_.emplace(&*parse_tree_, check_ir_id_, parse_tree_->packaging_decl(),
                   value_stores_, input_filename_);
-  if (!llvm_context_) {
-    llvm_context_ = std::make_unique<llvm::LLVMContext>();
-  }
   return {.consumer = consumer_,
           .value_stores = &value_stores_,
           .timings = timings_ ? &*timings_ : nullptr,
           .sem_ir = &*sem_ir_,
-          .llvm_context = llvm_context_.get(),
+          .llvm_context = llvm_context_,
           .total_ir_count = total_ir_count_};
 }
 
@@ -180,9 +176,6 @@ auto CompilationUnit::PostCheck() -> void {
 
 auto CompilationUnit::RunLower() -> void {
   LogCall("Lower::LowerToLLVM", "lower", [&] {
-    if (!llvm_context_) {
-      llvm_context_ = std::make_unique<llvm::LLVMContext>();
-    }
     Lower::LowerToLLVMOptions options;
     options.llvm_verifier_stream =
         options_->run_llvm_verifier ? driver_env_->error_stream : nullptr;
@@ -498,6 +491,8 @@ auto CompileDriver::Initialize(
     }
   }
 
+  llvm_context_ = std::make_unique<llvm::LLVMContext>();
+
   // Prepare CompilationUnits before building scope exit handlers.
   int unit_index = -1;
   int total_unit_count =
@@ -506,7 +501,8 @@ auto CompileDriver::Initialize(
     ++unit_index;
     return std::make_unique<CompilationUnit>(
         SemIR::CheckIRId(unit_index), total_unit_count, &driver_env, options_,
-        driver_env.consumer, filename, map_input(filename), target);
+        driver_env.consumer, filename, map_input(filename), target,
+        llvm_context_.get());
   };
   llvm::append_range(units_, llvm::map_range(prelude, unit_builder));
   llvm::append_range(units_, llvm::map_range(core_library, unit_builder));
diff --git a/toolchain/driver/compile_driver.h b/toolchain/driver/compile_driver.h
index 35b3ee08a868..f421775683db 100644
--- a/toolchain/driver/compile_driver.h
+++ b/toolchain/driver/compile_driver.h
@@ -26,7 +26,8 @@ class CompilationUnit {
                            Diagnostics::Consumer* consumer,
                            llvm::StringRef input_filename,
                            std::string output_filename,
-                           const llvm::Target* target);
+                           const llvm::Target* target,
+                           llvm::LLVMContext* llvm_context);
 
   // Sets the multi-unit cache and initializes dependent member state.
   auto SetMultiUnitCache(MultiUnitCache* cache) -> void;
@@ -146,7 +147,7 @@ class CompilationUnit {
   mutable std::optional<Parse::TreeAndSubtrees> parse_tree_and_subtrees_;
   std::optional<std::function<auto()->const Parse::TreeAndSubtrees&>>
       tree_and_subtrees_getter_;
-  std::unique_ptr<llvm::LLVMContext> llvm_context_;
+  llvm::LLVMContext* llvm_context_ = nullptr;
   std::optional<SemIR::File> sem_ir_;
   std::unique_ptr<llvm::Module> module_;
   std::unique_ptr<llvm::TargetMachine> target_machine_;
@@ -260,6 +261,7 @@ class CompileDriver {
  private:
   CompileOptions* options_;
   size_t input_filenames_index_ = 0;
+  std::unique_ptr<llvm::LLVMContext> llvm_context_;
   llvm::SmallVector<std::unique_ptr<CompilationUnit>, 256> units_;
   std::unique_ptr<MultiUnitCache> cache_;
   std::shared_ptr<clang::CompilerInvocation> clang_invocation_;
diff --git a/toolchain/lower/context.cpp b/toolchain/lower/context.cpp
index db8b4a165f2d..915d270987fc 100644
--- a/toolchain/lower/context.cpp
+++ b/toolchain/lower/context.cpp
@@ -34,17 +34,16 @@ Context::Context(
     llvm::LLVMContext* llvm_context,
     llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem> fs, bool want_debug_info,
     const Parse::GetTreeAndSubtreesStore* tree_and_subtrees_getters,
-    clang::CodeGenerator* clang_code_generator, llvm::StringRef module_name,
+    clang::CodeGenerator* cpp_code_generator, llvm::StringRef module_name,
     int total_ir_count, Lower::OptimizationLevel opt_level,
     bool mangle_string_fingerprint, llvm::raw_ostream* vlog_stream)
     : llvm_context_(llvm_context),
-      clang_code_generator_(clang_code_generator),
-      llvm_module_owner_(
-          clang_code_generator_
-              ? nullptr
-              : std::make_unique<llvm::Module>(module_name, *llvm_context)),
+      cpp_code_generator_(cpp_code_generator),
+      llvm_module_owner_(cpp_code_generator_ ? nullptr
+                                             : std::make_unique<llvm::Module>(
+                                                   module_name, *llvm_context)),
       llvm_module_(llvm_module_owner_ ? llvm_module_owner_.get()
-                                      : clang_code_generator_->GetModule()),
+                                      : cpp_code_generator_->GetModule()),
       file_system_(std::move(fs)),
       opt_level_(opt_level),
       di_builder_(*llvm_module_),
@@ -95,9 +94,9 @@ auto Context::Finalize() && -> std::unique_ptr<llvm::Module> {
                          "Debug Info Version", llvm::DEBUG_METADATA_VERSION);
   }
 
-  return clang_code_generator_ ? std::unique_ptr<llvm::Module>(
-                                     clang_code_generator_->ReleaseModule())
-                               : std::move(llvm_module_owner_);
+  return cpp_code_generator_ ? std::unique_ptr<llvm::Module>(
+                                   cpp_code_generator_->ReleaseModule())
+                             : std::move(llvm_module_owner_);
 }
 
 auto Context::BuildDICompileUnit(llvm::StringRef module_name,
diff --git a/toolchain/lower/context.h b/toolchain/lower/context.h
index 6a61f04ac2b1..60f9e0162553 100644
--- a/toolchain/lower/context.h
+++ b/toolchain/lower/context.h
@@ -121,6 +121,9 @@ class Context {
   auto file_system() -> llvm::IntrusiveRefCntPtr<llvm::vfs::FileSystem>& {
     return file_system_;
   }
+  auto cpp_code_generator() -> clang::CodeGenerator* {
+    return cpp_code_generator_;
+  }
   auto opt_level() -> Lower::OptimizationLevel { return opt_level_; }
   auto di_builder() -> llvm::DIBuilder& { return di_builder_; }
   auto di_compile_unit() -> llvm::DICompileUnit* { return di_compile_unit_; }
@@ -153,7 +156,7 @@ class Context {
 
   // State for building the LLVM IR.
   llvm::LLVMContext* llvm_context_;
-  clang::CodeGenerator* clang_code_generator_;
+  clang::CodeGenerator* cpp_code_generator_;
   std::unique_ptr<llvm::Module> llvm_module_owner_;
   llvm::Module* llvm_module_;
 
diff --git a/toolchain/lower/file_context.cpp b/toolchain/lower/file_context.cpp
index a00b7b1247e4..11e64ec1bc7e 100644
--- a/toolchain/lower/file_context.cpp
+++ b/toolchain/lower/file_context.cpp
@@ -63,11 +63,6 @@ FileContext::FileContext(Context& context, const SemIR::File& sem_ir,
       coalescer_(vlog_stream_, sem_ir.specifics()),
       vtables_(decltype(vtables_)::MakeForOverwrite(sem_ir.vtables())),
       specific_vtables_(sem_ir.specifics(), nullptr) {
-  // Initialization that relies on invariants of the class.
-  cpp_code_generator_ = cpp_file() ? cpp_file()->GetCodeGenerator() : nullptr;
-  CARBON_CHECK(
-      !cpp_code_generator_ ||
-      (&cpp_code_generator_->GetModule()->getContext() == &llvm_context()));
   CARBON_CHECK(!sem_ir.has_errors(),
                "Generating LLVM IR from invalid SemIR::File is unsupported.");
 }
@@ -184,10 +179,14 @@ auto FileContext::LowerDefinitions() -> void {
 }
 
 auto FileContext::Finalize() -> void {
-  if (cpp_code_generator_) {
+  // TODO: This is an ugly way to check if we're supposed to finalize this code
+  // generator. Context::Finalize should finalize its own code generator, but
+  // doesn't have a reference to its `ASTContext`.
+  if (cpp_file() &&
+      cpp_file()->code_generator() == context().cpp_code_generator()) {
     // Clang code generation should not actually modify the AST, but isn't
     // const-correct.
-    cpp_code_generator_->HandleTranslationUnit(
+    cpp_file()->code_generator()->HandleTranslationUnit(
         const_cast<clang::ASTContext&>(cpp_file()->ast_context()));
   }
 
@@ -316,9 +315,12 @@ auto FileContext::HandleReferencedCppFunction(clang::FunctionDecl* cpp_decl)
   // so that code generation (`CodeGenModule::EmitGlobal()`) would see this
   // function name (`CodeGenModule::getMangledName()`), and will generate
   // its definition.
-  auto* function_address = dyn_cast<llvm::Function>(
-      cpp_code_generator_->GetAddrOfGlobal(CreateGlobalDecl(cpp_decl),
-                                           /*isForDefinition=*/false));
+  // TODO: This code generator can be for the wrong AST if we're not using
+  // --share-cpp-ast.
+  auto* function_address =
+      dyn_cast<llvm::Function>(context().cpp_code_generator()->GetAddrOfGlobal(
+          CreateGlobalDecl(cpp_decl),
+          /*isForDefinition=*/false));
   CARBON_CHECK(function_address);
 
   return function_address;
@@ -724,7 +726,9 @@ auto FileContext::BuildGlobalVariableDecl(SemIR::VarStorage var_storage)
   // llvm::GlobalVariable.
   if (const auto* clang_decl =
           sem_ir().clang_decls().Lookup(var_storage.pattern_id)) {
-    auto* constant = cpp_code_generator_->GetAddrOfGlobal(
+    // TODO: This code generator can be for the wrong AST if we're not using
+    // --share-cpp-ast.
+    auto* constant = context().cpp_code_generator()->GetAddrOfGlobal(
         CreateGlobalDecl(cast<clang::NamedDecl>(clang_decl->decl())),
         /*isForDefinition=*/false);
     if (constant) {
@@ -772,7 +776,9 @@ auto FileContext::BuildVtable(const SemIR::Vtable& vtable,
   if (!vtable.carbon_native_vtable) {
     auto* cxx_record_decl = cast<clang::CXXRecordDecl>(
         sem_ir().clang_decls().Lookup(class_info.latest_decl_id())->key.decl);
-    return cpp_code_generator_->GetAddrOfVTable(
+    // TODO: This code generator can be for the wrong AST if we're not using
+    // --share-cpp-ast.
+    return context().cpp_code_generator()->GetAddrOfVTable(
         clang::BaseSubobject(cxx_record_decl,
                              clang::CharUnits::fromQuantity(0)),
         cxx_record_decl);
diff --git a/toolchain/lower/file_context.h b/toolchain/lower/file_context.h
index b135a2f517ff..cc9a18fc4d3c 100644
--- a/toolchain/lower/file_context.h
+++ b/toolchain/lower/file_context.h
@@ -166,10 +166,6 @@ class FileContext {
   auto context() -> Context& { return *context_; }
   auto llvm_context() -> llvm::LLVMContext& { return context().llvm_context(); }
   auto llvm_module() -> llvm::Module& { return context().llvm_module(); }
-  auto cpp_code_generator() -> clang::CodeGenerator& {
-    CARBON_CHECK(cpp_code_generator_);
-    return *cpp_code_generator_;
-  }
   auto sem_ir() const -> const SemIR::File& { return *sem_ir_; }
   auto cpp_file() -> const SemIR::CppFile* { return sem_ir().cpp_file(); }
   auto inst_namer() -> const SemIR::InstNamer* { return inst_namer_; }
@@ -270,10 +266,6 @@ class FileContext {
   // The input SemIR.
   const SemIR::File* const sem_ir_;
 
-  // The Clang `CodeGenerator` to generate LLVM module from imported C++
-  // code. Can be null if no C++ code is imported.
-  clang::CodeGenerator* cpp_code_generator_;
-
   // The instruction namer, if given.
   const SemIR::InstNamer* const inst_namer_;
 
diff --git a/toolchain/lower/handle_call.cpp b/toolchain/lower/handle_call.cpp
index b37fa1d078b7..a5722af833ae 100644
--- a/toolchain/lower/handle_call.cpp
+++ b/toolchain/lower/handle_call.cpp
@@ -744,9 +744,17 @@ auto HandleInst(FunctionContext& context, SemIR::InstId inst_id,
   // Lower args in the LLVM parameter order, rather than the SemIR parameter
   // order.
   std::vector<llvm::Value*> args;
+  bool args_ok = true;
+  auto* callee_type = function_info->llvm_function->getFunctionType();
   for (auto index : function_info->lowered_param_indices) {
     args.push_back(context.GetValue(arg_ids[index.index]));
+
+    if (args.size() > callee_type->getNumParams() ||
+        callee_type->getParamType(args.size() - 1) != args.back()->getType()) {
+      args_ok = false;
+    }
   }
+  args_ok &= args.size() == callee_type->getNumParams();
 
   llvm::CallInst* call;
   if (function.virtual_index == -1) {
@@ -765,8 +773,7 @@ auto HandleInst(FunctionContext& context, SemIR::InstId inst_id,
       llvm_callee->print(out);
       return out.TakeStr();
     };
-    CARBON_CHECK(llvm_callee->arg_size() == args.size(),
-                 "Argument count mismatch: {0}", describe_call());
+    CARBON_CHECK(args_ok, "Argument mismatch: {0}", describe_call());
     call = context.builder().CreateCall(llvm_callee, args);
   } else {
     call = HandleVirtualCall(context, args, function, *function_info);
diff --git a/toolchain/lower/lower.cpp b/toolchain/lower/lower.cpp
index 5101dd3cf83c..83d24b2c2243 100644
--- a/toolchain/lower/lower.cpp
+++ b/toolchain/lower/lower.cpp
@@ -23,7 +23,7 @@ auto LowerToLLVM(
   Context context(
       &llvm_context, std::move(fs), options.want_debug_info,
       &tree_and_subtrees_getters,
-      sem_ir.cpp_file() ? sem_ir.cpp_file()->GetCodeGenerator() : nullptr,
+      sem_ir.cpp_file() ? sem_ir.cpp_file()->code_generator() : nullptr,
       sem_ir.filename(), total_ir_count, options.opt_level,
       options.mangle_string_fingerprint, options.vlog_stream);
 
diff --git a/toolchain/lower/testdata/function/generic/call.carbon b/toolchain/lower/testdata/function/generic/call.carbon
index 7872988602b7..47af9f4c7f69 100644
--- a/toolchain/lower/testdata/function/generic/call.carbon
+++ b/toolchain/lower/testdata/function/generic/call.carbon
@@ -33,7 +33,7 @@ fn G() {
 // CHECK:STDOUT: ; ModuleID = 'call.carbon'
 // CHECK:STDOUT: source_filename = "call.carbon"
 // CHECK:STDOUT:
-// CHECK:STDOUT: %type = type {}
+// CHECK:STDOUT: %type.26 = type {}
 // CHECK:STDOUT:
 // CHECK:STDOUT: @C.val.loc20_3 = internal constant {} zeroinitializer
 // CHECK:STDOUT: @D.val.loc21_3 = internal constant {} zeroinitializer
@@ -59,7 +59,7 @@ fn G() {
 // CHECK:STDOUT:   call void @_CF.Main.84588f41d61dafba(i32 %.loc27), !dbg !14
 // CHECK:STDOUT:   %.loc28 = load double, ptr %m.var, align 8, !dbg !15
 // CHECK:STDOUT:   call void @_CF.Main.073fbce68be6103e(double %.loc28), !dbg !16
-// CHECK:STDOUT:   call void @_CF.Main.5754c7a55c7cbe4a(%type zeroinitializer), !dbg !17
+// CHECK:STDOUT:   call void @_CF.Main.5754c7a55c7cbe4a(%type.26 zeroinitializer), !dbg !17
 // CHECK:STDOUT:   call void @"_COp.30d8007fdcc57f83:core.Destroy.Core"(ptr %m.var), !dbg !10
 // CHECK:STDOUT:   call void @"_COp.5e27612b9dd31a14:core.Destroy.Core"(ptr %n.var), !dbg !9
 // CHECK:STDOUT:   call void @"_COp.7fd3b6c3a3c15807:core.Destroy.Core"(ptr %d.var), !dbg !8
@@ -116,7 +116,7 @@ fn G() {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr void @_CF.Main.5754c7a55c7cbe4a(%type %_) #0 !dbg !53 {
+// CHECK:STDOUT: define linkonce_odr void @_CF.Main.5754c7a55c7cbe4a(%type.26 %_) #0 !dbg !53 {
 // CHECK:STDOUT: entry:
 // CHECK:STDOUT:   ret void, !dbg !56
 // CHECK:STDOUT: }
diff --git a/toolchain/lower/testdata/function/generic/call_basic.carbon b/toolchain/lower/testdata/function/generic/call_basic.carbon
index c84994ed7438..1278139b46c9 100644
--- a/toolchain/lower/testdata/function/generic/call_basic.carbon
+++ b/toolchain/lower/testdata/function/generic/call_basic.carbon
@@ -59,7 +59,7 @@ fn M() {
 // CHECK:STDOUT: ; ModuleID = 'call_basic.carbon'
 // CHECK:STDOUT: source_filename = "call_basic.carbon"
 // CHECK:STDOUT:
-// CHECK:STDOUT: %type = type {}
+// CHECK:STDOUT: %type.26 = type {}
 // CHECK:STDOUT:
 // CHECK:STDOUT: @C.val.loc15_43 = internal constant {} zeroinitializer
 // CHECK:STDOUT:
@@ -138,7 +138,7 @@ fn M() {
 // CHECK:STDOUT:   %H.call.loc29 = call i32 @_CH.Main.5bd8d5767580997a(i32 %x), !dbg !51
 // CHECK:STDOUT:   store i32 %H.call.loc29, ptr %.loc29_6.3.temp, align 4, !dbg !51
 // CHECK:STDOUT:   call void @"_COp.5e27612b9dd31a14:core.Destroy.Core"(ptr %.loc29_6.3.temp), !dbg !51
-// CHECK:STDOUT:   %H.call.loc30 = call %type @_CH.Main.ee509b43cf4eb3c5(%type zeroinitializer), !dbg !60
+// CHECK:STDOUT:   %H.call.loc30 = call %type.26 @_CH.Main.ee509b43cf4eb3c5(%type.26 zeroinitializer), !dbg !60
 // CHECK:STDOUT:   call void @llvm.lifetime.start.p0(ptr %.loc31_8.3.temp), !dbg !52
 // CHECK:STDOUT:   %G.call = call i32 @_CG.Main.58016a73bff04416(i32 %x), !dbg !52
 // CHECK:STDOUT:   call void @llvm.lifetime.start.p0(ptr %.loc31_9.3.temp), !dbg !53
@@ -195,7 +195,7 @@ fn M() {
 // CHECK:STDOUT:   %H.call.loc29 = call double @_CH.Main.c27b765f2159c9a0(double %x), !dbg !77
 // CHECK:STDOUT:   store double %H.call.loc29, ptr %.loc29_6.3.temp, align 8, !dbg !77
 // CHECK:STDOUT:   call void @"_COp.30d8007fdcc57f83:core.Destroy.Core"(ptr %.loc29_6.3.temp), !dbg !77
-// CHECK:STDOUT:   %H.call.loc30 = call %type @_CH.Main.ee509b43cf4eb3c5(%type zeroinitializer), !dbg !86
+// CHECK:STDOUT:   %H.call.loc30 = call %type.26 @_CH.Main.ee509b43cf4eb3c5(%type.26 zeroinitializer), !dbg !86
 // CHECK:STDOUT:   call void @llvm.lifetime.start.p0(ptr %.loc31_8.3.temp), !dbg !78
 // CHECK:STDOUT:   %G.call = call double @_CG.Main.fa1f0912a5bbe922(double %x), !dbg !78
 // CHECK:STDOUT:   call void @llvm.lifetime.start.p0(ptr %.loc31_9.3.temp), !dbg !79
@@ -237,9 +237,9 @@ fn M() {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr %type @_CH.Main.ee509b43cf4eb3c5(%type %x) #0 !dbg !100 {
+// CHECK:STDOUT: define linkonce_odr %type.26 @_CH.Main.ee509b43cf4eb3c5(%type.26 %x) #0 !dbg !100 {
 // CHECK:STDOUT: entry:
-// CHECK:STDOUT:   ret %type %x, !dbg !103
+// CHECK:STDOUT:   ret %type.26 %x, !dbg !103
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
diff --git a/toolchain/lower/testdata/function/generic/call_deref_ptr.carbon b/toolchain/lower/testdata/function/generic/call_deref_ptr.carbon
index 3b7850c12933..11997ae2eb3b 100644
--- a/toolchain/lower/testdata/function/generic/call_deref_ptr.carbon
+++ b/toolchain/lower/testdata/function/generic/call_deref_ptr.carbon
@@ -44,7 +44,7 @@ fn M() {
 // CHECK:STDOUT: ; ModuleID = 'call_deref_ptr.carbon'
 // CHECK:STDOUT: source_filename = "call_deref_ptr.carbon"
 // CHECK:STDOUT:
-// CHECK:STDOUT: %type = type {}
+// CHECK:STDOUT: %type.26 = type {}
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
 // CHECK:STDOUT: define void @_CM.Main() #0 !dbg !4 {
@@ -80,7 +80,7 @@ fn M() {
 // CHECK:STDOUT: ; Function Attrs: nounwind
 // CHECK:STDOUT: define linkonce_odr void @_CF.Main.58016a73bff04416(ptr %x) #0 !dbg !28 {
 // CHECK:STDOUT: entry:
-// CHECK:STDOUT:   %A.call = call %type @_CA.Main.ee509b43cf4eb3c5(%type zeroinitializer), !dbg !31
+// CHECK:STDOUT:   %A.call = call %type.26 @_CA.Main.ee509b43cf4eb3c5(%type.26 zeroinitializer), !dbg !31
 // CHECK:STDOUT:   call void @_CB.Main.58016a73bff04416(ptr %x), !dbg !32
 // CHECK:STDOUT:   ret void, !dbg !33
 // CHECK:STDOUT: }
@@ -88,15 +88,15 @@ fn M() {
 // CHECK:STDOUT: ; Function Attrs: nounwind
 // CHECK:STDOUT: define linkonce_odr void @_CF.Main.fa1f0912a5bbe922(ptr %x) #0 !dbg !34 {
 // CHECK:STDOUT: entry:
-// CHECK:STDOUT:   %A.call = call %type @_CA.Main.ee509b43cf4eb3c5(%type zeroinitializer), !dbg !37
+// CHECK:STDOUT:   %A.call = call %type.26 @_CA.Main.ee509b43cf4eb3c5(%type.26 zeroinitializer), !dbg !37
 // CHECK:STDOUT:   call void @_CB.Main.fa1f0912a5bbe922(ptr %x), !dbg !38
 // CHECK:STDOUT:   ret void, !dbg !39
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr %type @_CA.Main.ee509b43cf4eb3c5(%type %x) #0 !dbg !40 {
+// CHECK:STDOUT: define linkonce_odr %type.26 @_CA.Main.ee509b43cf4eb3c5(%type.26 %x) #0 !dbg !40 {
 // CHECK:STDOUT: entry:
-// CHECK:STDOUT:   ret %type %x, !dbg !45
+// CHECK:STDOUT:   ret %type.26 %x, !dbg !45
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
diff --git a/toolchain/lower/testdata/function/generic/call_different_specific.carbon b/toolchain/lower/testdata/function/generic/call_different_specific.carbon
index d10edc0dae35..dc454daec477 100644
--- a/toolchain/lower/testdata/function/generic/call_different_specific.carbon
+++ b/toolchain/lower/testdata/function/generic/call_different_specific.carbon
@@ -48,7 +48,7 @@ fn M(ptr_i32: i32*, ptr_f64: f64*) {
 // CHECK:STDOUT: ; ModuleID = 'call_different_specific.carbon'
 // CHECK:STDOUT: source_filename = "call_different_specific.carbon"
 // CHECK:STDOUT:
-// CHECK:STDOUT: %type = type {}
+// CHECK:STDOUT: %type.58 = type {}
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
 // CHECK:STDOUT: define void @_CM.Main(ptr %ptr_i32, ptr %ptr_f64) #0 !dbg !4 {
@@ -73,7 +73,7 @@ fn M(ptr_i32: i32*, ptr_f64: f64*) {
 // CHECK:STDOUT: ; Function Attrs: nounwind
 // CHECK:STDOUT: define linkonce_odr void @_CF.Main.58016a73bff04416(ptr %x) #0 !dbg !27 {
 // CHECK:STDOUT: entry:
-// CHECK:STDOUT:   %A.call = call %type @_CA.Main.ee509b43cf4eb3c5(%type zeroinitializer), !dbg !30
+// CHECK:STDOUT:   %A.call = call %type.58 @_CA.Main.ee509b43cf4eb3c5(%type.58 zeroinitializer), !dbg !30
 // CHECK:STDOUT:   call void @_CB.Main.58016a73bff04416(ptr %x), !dbg !31
 // CHECK:STDOUT:   ret void, !dbg !32
 // CHECK:STDOUT: }
@@ -81,15 +81,15 @@ fn M(ptr_i32: i32*, ptr_f64: f64*) {
 // CHECK:STDOUT: ; Function Attrs: nounwind
 // CHECK:STDOUT: define linkonce_odr void @_CF.Main.fa1f0912a5bbe922(ptr %x) #0 !dbg !33 {
 // CHECK:STDOUT: entry:
-// CHECK:STDOUT:   %A.call = call %type @_CA.Main.ee509b43cf4eb3c5(%type zeroinitializer), !dbg !36
+// CHECK:STDOUT:   %A.call = call %type.58 @_CA.Main.ee509b43cf4eb3c5(%type.58 zeroinitializer), !dbg !36
 // CHECK:STDOUT:   call void @_CB.Main.fa1f0912a5bbe922(ptr %x), !dbg !37
 // CHECK:STDOUT:   ret void, !dbg !38
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr %type @_CA.Main.ee509b43cf4eb3c5(%type %x) #0 !dbg !39 {
+// CHECK:STDOUT: define linkonce_odr %type.58 @_CA.Main.ee509b43cf4eb3c5(%type.58 %x) #0 !dbg !39 {
 // CHECK:STDOUT: entry:
-// CHECK:STDOUT:   ret %type %x, !dbg !44
+// CHECK:STDOUT:   ret %type.58 %x, !dbg !44
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
diff --git a/toolchain/lower/testdata/function/generic/call_specific_in_class.carbon b/toolchain/lower/testdata/function/generic/call_specific_in_class.carbon
index db4d28deca30..11ed3eb270bb 100644
--- a/toolchain/lower/testdata/function/generic/call_specific_in_class.carbon
+++ b/toolchain/lower/testdata/function/generic/call_specific_in_class.carbon
@@ -48,7 +48,7 @@ fn M() {
 // CHECK:STDOUT: ; ModuleID = 'call_specific_in_class.carbon'
 // CHECK:STDOUT: source_filename = "call_specific_in_class.carbon"
 // CHECK:STDOUT:
-// CHECK:STDOUT: %type = type {}
+// CHECK:STDOUT: %type.26 = type {}
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
 // CHECK:STDOUT: define weak_odr void @"_COp.807eb4f2d3ed7e54:core.Destroy.Core"(ptr %self) #0 !dbg !4 {
@@ -86,7 +86,7 @@ fn M() {
 // CHECK:STDOUT:   %.loc42_5 = load double, ptr %var_f64.var, align 8, !dbg !28
 // CHECK:STDOUT:   %F.call.loc42 = call double @_CF.Main.c27b765f2159c9a0(double %.loc42_5), !dbg !29
 // CHECK:STDOUT:   call void @llvm.lifetime.start.p0(ptr %_.var), !dbg !19
-// CHECK:STDOUT:   %F.call.loc44 = call %type @_CF.Main.ee509b43cf4eb3c5(%type zeroinitializer), !dbg !30
+// CHECK:STDOUT:   %F.call.loc44 = call %type.26 @_CF.Main.ee509b43cf4eb3c5(%type.26 zeroinitializer), !dbg !30
 // CHECK:STDOUT:   call void @"_COp.807eb4f2d3ed7e54:core.Destroy.Core"(ptr %_.var), !dbg !19
 // CHECK:STDOUT:   call void @"_COp.30d8007fdcc57f83:core.Destroy.Core"(ptr %var_f64.var), !dbg !18
 // CHECK:STDOUT:   call void @"_COp.5e27612b9dd31a14:core.Destroy.Core"(ptr %var_i32.var), !dbg !17
@@ -130,10 +130,10 @@ fn M() {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr %type @_CF.Main.ee509b43cf4eb3c5(%type %x) #0 !dbg !62 {
+// CHECK:STDOUT: define linkonce_odr %type.26 @_CF.Main.ee509b43cf4eb3c5(%type.26 %x) #0 !dbg !62 {
 // CHECK:STDOUT: entry:
-// CHECK:STDOUT:   %G.call = call %type @_CG.Main.ee509b43cf4eb3c5(%type %x), !dbg !65
-// CHECK:STDOUT:   ret %type %G.call, !dbg !66
+// CHECK:STDOUT:   %G.call = call %type.26 @_CG.Main.ee509b43cf4eb3c5(%type.26 %x), !dbg !65
+// CHECK:STDOUT:   ret %type.26 %G.call, !dbg !66
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
@@ -167,13 +167,13 @@ fn M() {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr %type @_CG.Main.ee509b43cf4eb3c5(%type %x) #0 !dbg !85 {
+// CHECK:STDOUT: define linkonce_odr %type.26 @_CG.Main.ee509b43cf4eb3c5(%type.26 %x) #0 !dbg !85 {
 // CHECK:STDOUT: entry:
 // CHECK:STDOUT:   %c.var = alloca {}, align 1, !dbg !88
 // CHECK:STDOUT:   call void @llvm.lifetime.start.p0(ptr %c.var), !dbg !88
-// CHECK:STDOUT:   %C.Cfn.call = call %type @_CCfn.C.Main.ee509b43cf4eb3c5(ptr %c.var, %type %x), !dbg !89
+// CHECK:STDOUT:   %C.Cfn.call = call %type.26 @_CCfn.C.Main.ee509b43cf4eb3c5(ptr %c.var, %type.26 %x), !dbg !89
 // CHECK:STDOUT:   call void @"_COp.807eb4f2d3ed7e54:core.Destroy.Core"(ptr %c.var), !dbg !88
-// CHECK:STDOUT:   ret %type %C.Cfn.call, !dbg !90
+// CHECK:STDOUT:   ret %type.26 %C.Cfn.call, !dbg !90
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
@@ -195,9 +195,9 @@ fn M() {
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define linkonce_odr %type @_CCfn.C.Main.ee509b43cf4eb3c5(ptr %self, %type %x) #0 !dbg !110 {
+// CHECK:STDOUT: define linkonce_odr %type.26 @_CCfn.C.Main.ee509b43cf4eb3c5(ptr %self, %type.26 %x) #0 !dbg !110 {
 // CHECK:STDOUT: entry:
-// CHECK:STDOUT:   ret %type %x, !dbg !114
+// CHECK:STDOUT:   ret %type.26 %x, !dbg !114
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; uselistorder directives
diff --git a/toolchain/lower/testdata/interop/cpp/class/export/class.carbon b/toolchain/lower/testdata/interop/cpp/class/export/class.carbon
index 0f11fd76ebca..82ff728f5950 100644
--- a/toolchain/lower/testdata/interop/cpp/class/export/class.carbon
+++ b/toolchain/lower/testdata/interop/cpp/class/export/class.carbon
@@ -458,7 +458,7 @@ fn G() {
 // CHECK:STDOUT: target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
 // CHECK:STDOUT: target triple = "x86_64-unknown-linux-gnu"
 // CHECK:STDOUT:
-// CHECK:STDOUT: %"class.Carbon::C" = type { i32, i32 }
+// CHECK:STDOUT: %"class.Carbon::C.0" = type { i32, i32 }
 // CHECK:STDOUT:
 // CHECK:STDOUT: @C.val.loc19_3 = internal constant { i32, i32 } zeroinitializer
 // CHECK:STDOUT:
@@ -468,10 +468,10 @@ fn G() {
 // CHECK:STDOUT:   %c.addr = alloca ptr, align 8
 // CHECK:STDOUT:   store ptr %c, ptr %c.addr, align 8, !tbaa !12
 // CHECK:STDOUT:   %0 = load ptr, ptr %c.addr, align 8, !tbaa !12, !nonnull !15, !align !16
-// CHECK:STDOUT:   %a = getelementptr inbounds nuw %"class.Carbon::C", ptr %0, i32 0, i32 0
+// CHECK:STDOUT:   %a = getelementptr inbounds nuw %"class.Carbon::C.0", ptr %0, i32 0, i32 0
 // CHECK:STDOUT:   store i32 12, ptr %a, align 4, !tbaa !17
 // CHECK:STDOUT:   %1 = load ptr, ptr %c.addr, align 8, !tbaa !12, !nonnull !15, !align !16
-// CHECK:STDOUT:   %b = getelementptr inbounds nuw %"class.Carbon::C", ptr %1, i32 0, i32 1
+// CHECK:STDOUT:   %b = getelementptr inbounds nuw %"class.Carbon::C.0", ptr %1, i32 0, i32 1
 // CHECK:STDOUT:   store i32 34, ptr %b, align 4, !tbaa !19
 // CHECK:STDOUT:   ret void
 // CHECK:STDOUT: }
diff --git a/toolchain/lower/testdata/interop/cpp/class/export/method.carbon b/toolchain/lower/testdata/interop/cpp/class/export/method.carbon
index 73a87ea14a8f..79f74f5f322e 100644
--- a/toolchain/lower/testdata/interop/cpp/class/export/method.carbon
+++ b/toolchain/lower/testdata/interop/cpp/class/export/method.carbon
@@ -188,14 +188,14 @@ fn CallCallF() { Cpp.CallF(); }
 // CHECK:STDOUT: target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
 // CHECK:STDOUT: target triple = "x86_64-unknown-linux-gnu"
 // CHECK:STDOUT:
-// CHECK:STDOUT: %"class.Carbon::A" = type {}
+// CHECK:STDOUT: %"class.Carbon::A.0" = type {}
 // CHECK:STDOUT:
 // CHECK:STDOUT: $_ZN6Carbon1AD2Ev = comdat any
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: mustprogress nounwind uwtable
 // CHECK:STDOUT: define dso_local noundef i32 @_Z5CallFv() #0 {
 // CHECK:STDOUT: entry:
-// CHECK:STDOUT:   %ref.tmp = alloca %"class.Carbon::A", align 1
+// CHECK:STDOUT:   %ref.tmp = alloca %"class.Carbon::A.0", align 1
 // CHECK:STDOUT:   call void @llvm.lifetime.start.p0(ptr %ref.tmp) #4
 // CHECK:STDOUT:   %call = call noundef i32 @_ZNK6Carbon1A1FEi(ptr noundef nonnull align 1 %ref.tmp, i32 noundef 123)
 // CHECK:STDOUT:   call void @_ZN6Carbon1AD2Ev(ptr noundef nonnull align 1 %ref.tmp) #4
diff --git a/toolchain/lower/testdata/interop/cpp/class/import/constructor.carbon b/toolchain/lower/testdata/interop/cpp/class/import/constructor.carbon
index 6a544bf3cde2..8ae6417f3d19 100644
--- a/toolchain/lower/testdata/interop/cpp/class/import/constructor.carbon
+++ b/toolchain/lower/testdata/interop/cpp/class/import/constructor.carbon
@@ -276,7 +276,7 @@ fn Four() {
 // CHECK:STDOUT: target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
 // CHECK:STDOUT: target triple = "x86_64-unknown-linux-gnu"
 // CHECK:STDOUT:
-// CHECK:STDOUT: %class.C = type { i32, i32 }
+// CHECK:STDOUT: %class.C.18 = type { i32, i32 }
 // CHECK:STDOUT:
 // CHECK:STDOUT: $_ZN1CC2Ev = comdat any
 // CHECK:STDOUT:
@@ -321,9 +321,9 @@ fn Four() {
 // CHECK:STDOUT:   %this.addr = alloca ptr, align 8
 // CHECK:STDOUT:   store ptr %this, ptr %this.addr, align 8, !tbaa !17
 // CHECK:STDOUT:   %this1 = load ptr, ptr %this.addr, align 8
-// CHECK:STDOUT:   %x_ = getelementptr inbounds nuw %class.C, ptr %this1, i32 0, i32 0
+// CHECK:STDOUT:   %x_ = getelementptr inbounds nuw %class.C.18, ptr %this1, i32 0, i32 0
 // CHECK:STDOUT:   store i32 8, ptr %x_, align 4, !tbaa !30
-// CHECK:STDOUT:   %y_ = getelementptr inbounds nuw %class.C, ptr %this1, i32 0, i32 1
+// CHECK:STDOUT:   %y_ = getelementptr inbounds nuw %class.C.18, ptr %this1, i32 0, i32 1
 // CHECK:STDOUT:   store i32 9, ptr %y_, align 4, !tbaa !32
 // CHECK:STDOUT:   ret void
 // CHECK:STDOUT: }
diff --git a/toolchain/lower/testdata/interop/cpp/class/import/method.carbon b/toolchain/lower/testdata/interop/cpp/class/import/method.carbon
index 8c7dd90ef293..477067ab5b44 100644
--- a/toolchain/lower/testdata/interop/cpp/class/import/method.carbon
+++ b/toolchain/lower/testdata/interop/cpp/class/import/method.carbon
@@ -184,8 +184,8 @@ fn F(ref r: Cpp.A) {
 // CHECK:STDOUT: target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
 // CHECK:STDOUT: target triple = "x86_64-unknown-linux-gnu"
 // CHECK:STDOUT:
-// CHECK:STDOUT: %struct.A = type <{ %struct.Base, i32, [4 x i8] }>
-// CHECK:STDOUT: %struct.Base = type { ptr }
+// CHECK:STDOUT: %struct.A.18 = type <{ %struct.Base.19, i32, [4 x i8] }>
+// CHECK:STDOUT: %struct.Base.19 = type { ptr }
 // CHECK:STDOUT:
 // CHECK:STDOUT: $_ZN1A6by_refEv = comdat any
 // CHECK:STDOUT:
@@ -211,7 +211,7 @@ fn F(ref r: Cpp.A) {
 // CHECK:STDOUT:   %this.addr = alloca ptr, align 8
 // CHECK:STDOUT:   store ptr %this, ptr %this.addr, align 8, !tbaa !21
 // CHECK:STDOUT:   %this1 = load ptr, ptr %this.addr, align 8
-// CHECK:STDOUT:   %n = getelementptr inbounds nuw %struct.A, ptr %this1, i32 0, i32 1
+// CHECK:STDOUT:   %n = getelementptr inbounds nuw %struct.A.18, ptr %this1, i32 0, i32 1
 // CHECK:STDOUT:   %0 = load i32, ptr %n, align 8, !tbaa !24
 // CHECK:STDOUT:   ret i32 %0
 // CHECK:STDOUT: }
diff --git a/toolchain/lower/testdata/interop/cpp/globals.carbon b/toolchain/lower/testdata/interop/cpp/globals.carbon
index 0aedb0a9e113..97f39c42a0c7 100644
--- a/toolchain/lower/testdata/interop/cpp/globals.carbon
+++ b/toolchain/lower/testdata/interop/cpp/globals.carbon
@@ -528,10 +528,10 @@ fn ReadStaticVarTemplateWithConstructor() -> Cpp.Y* {
 // CHECK:STDOUT: target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
 // CHECK:STDOUT: target triple = "x86_64-unknown-linux-gnu"
 // CHECK:STDOUT:
-// CHECK:STDOUT: %struct.Y = type { i8 }
+// CHECK:STDOUT: %struct.Y.26 = type { i8 }
 // CHECK:STDOUT:
 // CHECK:STDOUT: @_ZN1X11static_tmplIiEE = external global i32, align 4
-// CHECK:STDOUT: @_ZN1X11static_tmplI1YEE = external global %struct.Y, align 1
+// CHECK:STDOUT: @_ZN1X11static_tmplI1YEE = external global %struct.Y.26, align 1
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
 // CHECK:STDOUT: define i32 @_CReadStaticVarTemplate.Main() #0 !dbg !12 {
diff --git a/toolchain/lower/testdata/interop/cpp/operators.carbon b/toolchain/lower/testdata/interop/cpp/operators.carbon
index d1de98480052..610f3dad578a 100644
--- a/toolchain/lower/testdata/interop/cpp/operators.carbon
+++ b/toolchain/lower/testdata/interop/cpp/operators.carbon
@@ -290,7 +290,7 @@ fn Driver(x: Cpp.A, y: Cpp.A) {
 // CHECK:STDOUT: target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
 // CHECK:STDOUT: target triple = "x86_64-unknown-linux-gnu"
 // CHECK:STDOUT:
-// CHECK:STDOUT: %struct.A = type { i32 }
+// CHECK:STDOUT: %struct.A.62 = type { i32 }
 // CHECK:STDOUT:
 // CHECK:STDOUT: $_Zlt1AS_ = comdat any
 // CHECK:STDOUT:
@@ -313,8 +313,8 @@ fn Driver(x: Cpp.A, y: Cpp.A) {
 // CHECK:STDOUT:   %x.addr = alloca ptr, align 8
 // CHECK:STDOUT:   %y.addr = alloca ptr, align 8
 // CHECK:STDOUT:   %return.addr = alloca ptr, align 8
-// CHECK:STDOUT:   %agg.tmp = alloca %struct.A, align 4
-// CHECK:STDOUT:   %agg.tmp1 = alloca %struct.A, align 4
+// CHECK:STDOUT:   %agg.tmp = alloca %struct.A.62, align 4
+// CHECK:STDOUT:   %agg.tmp1 = alloca %struct.A.62, align 4
 // CHECK:STDOUT:   store ptr %x, ptr %x.addr, align 8, !tbaa !21
 // CHECK:STDOUT:   store ptr %y, ptr %y.addr, align 8, !tbaa !21
 // CHECK:STDOUT:   store ptr %return, ptr %return.addr, align 8, !tbaa !24
@@ -323,9 +323,9 @@ fn Driver(x: Cpp.A, y: Cpp.A) {
 // CHECK:STDOUT:   call void @llvm.memcpy.p0.p0.i64(ptr align 4 %agg.tmp, ptr align 4 %1, i64 4, i1 false), !tbaa.struct !26
 // CHECK:STDOUT:   %2 = load ptr, ptr %y.addr, align 8, !tbaa !21
 // CHECK:STDOUT:   call void @llvm.memcpy.p0.p0.i64(ptr align 4 %agg.tmp1, ptr align 4 %2, i64 4, i1 false), !tbaa.struct !26
-// CHECK:STDOUT:   %coerce.dive = getelementptr inbounds nuw %struct.A, ptr %agg.tmp, i32 0, i32 0
+// CHECK:STDOUT:   %coerce.dive = getelementptr inbounds nuw %struct.A.62, ptr %agg.tmp, i32 0, i32 0
 // CHECK:STDOUT:   %3 = load i32, ptr %coerce.dive, align 4
-// CHECK:STDOUT:   %coerce.dive2 = getelementptr inbounds nuw %struct.A, ptr %agg.tmp1, i32 0, i32 0
+// CHECK:STDOUT:   %coerce.dive2 = getelementptr inbounds nuw %struct.A.62, ptr %agg.tmp1, i32 0, i32 0
 // CHECK:STDOUT:   %4 = load i32, ptr %coerce.dive2, align 4
 // CHECK:STDOUT:   %call = call noundef zeroext i1 @_Zlt1AS_(i32 %3, i32 %4)
 // CHECK:STDOUT:   %storedv = zext i1 %call to i8
@@ -339,8 +339,8 @@ fn Driver(x: Cpp.A, y: Cpp.A) {
 // CHECK:STDOUT:   %x.addr = alloca ptr, align 8
 // CHECK:STDOUT:   %y.addr = alloca ptr, align 8
 // CHECK:STDOUT:   %return.addr = alloca ptr, align 8
-// CHECK:STDOUT:   %agg.tmp = alloca %struct.A, align 4
-// CHECK:STDOUT:   %agg.tmp1 = alloca %struct.A, align 4
+// CHECK:STDOUT:   %agg.tmp = alloca %struct.A.62, align 4
+// CHECK:STDOUT:   %agg.tmp1 = alloca %struct.A.62, align 4
 // CHECK:STDOUT:   store ptr %x, ptr %x.addr, align 8, !tbaa !21
 // CHECK:STDOUT:   store ptr %y, ptr %y.addr, align 8, !tbaa !21
 // CHECK:STDOUT:   store ptr %return, ptr %return.addr, align 8, !tbaa !24
@@ -349,9 +349,9 @@ fn Driver(x: Cpp.A, y: Cpp.A) {
 // CHECK:STDOUT:   call void @llvm.memcpy.p0.p0.i64(ptr align 4 %agg.tmp, ptr align 4 %1, i64 4, i1 false), !tbaa.struct !26
 // CHECK:STDOUT:   %2 = load ptr, ptr %y.addr, align 8, !tbaa !21
 // CHECK:STDOUT:   call void @llvm.memcpy.p0.p0.i64(ptr align 4 %agg.tmp1, ptr align 4 %2, i64 4, i1 false), !tbaa.struct !26
-// CHECK:STDOUT:   %coerce.dive = getelementptr inbounds nuw %struct.A, ptr %agg.tmp, i32 0, i32 0
+// CHECK:STDOUT:   %coerce.dive = getelementptr inbounds nuw %struct.A.62, ptr %agg.tmp, i32 0, i32 0
 // CHECK:STDOUT:   %3 = load i32, ptr %coerce.dive, align 4
-// CHECK:STDOUT:   %coerce.dive2 = getelementptr inbounds nuw %struct.A, ptr %agg.tmp1, i32 0, i32 0
+// CHECK:STDOUT:   %coerce.dive2 = getelementptr inbounds nuw %struct.A.62, ptr %agg.tmp1, i32 0, i32 0
 // CHECK:STDOUT:   %4 = load i32, ptr %coerce.dive2, align 4
 // CHECK:STDOUT:   %call = call noundef zeroext i1 @_Zle1AS_(i32 %3, i32 %4)
 // CHECK:STDOUT:   %storedv = zext i1 %call to i8
@@ -365,8 +365,8 @@ fn Driver(x: Cpp.A, y: Cpp.A) {
 // CHECK:STDOUT:   %x.addr = alloca ptr, align 8
 // CHECK:STDOUT:   %y.addr = alloca ptr, align 8
 // CHECK:STDOUT:   %return.addr = alloca ptr, align 8
-// CHECK:STDOUT:   %agg.tmp = alloca %struct.A, align 4
-// CHECK:STDOUT:   %agg.tmp1 = alloca %struct.A, align 4
+// CHECK:STDOUT:   %agg.tmp = alloca %struct.A.62, align 4
+// CHECK:STDOUT:   %agg.tmp1 = alloca %struct.A.62, align 4
 // CHECK:STDOUT:   store ptr %x, ptr %x.addr, align 8, !tbaa !21
 // CHECK:STDOUT:   store ptr %y, ptr %y.addr, align 8, !tbaa !21
 // CHECK:STDOUT:   store ptr %return, ptr %return.addr, align 8, !tbaa !24
@@ -375,9 +375,9 @@ fn Driver(x: Cpp.A, y: Cpp.A) {
 // CHECK:STDOUT:   call void @llvm.memcpy.p0.p0.i64(ptr align 4 %agg.tmp, ptr align 4 %1, i64 4, i1 false), !tbaa.struct !26
 // CHECK:STDOUT:   %2 = load ptr, ptr %y.addr, align 8, !tbaa !21
 // CHECK:STDOUT:   call void @llvm.memcpy.p0.p0.i64(ptr align 4 %agg.tmp1, ptr align 4 %2, i64 4, i1 false), !tbaa.struct !26
-// CHECK:STDOUT:   %coerce.dive = getelementptr inbounds nuw %struct.A, ptr %agg.tmp, i32 0, i32 0
+// CHECK:STDOUT:   %coerce.dive = getelementptr inbounds nuw %struct.A.62, ptr %agg.tmp, i32 0, i32 0
 // CHECK:STDOUT:   %3 = load i32, ptr %coerce.dive, align 4
-// CHECK:STDOUT:   %coerce.dive2 = getelementptr inbounds nuw %struct.A, ptr %agg.tmp1, i32 0, i32 0
+// CHECK:STDOUT:   %coerce.dive2 = getelementptr inbounds nuw %struct.A.62, ptr %agg.tmp1, i32 0, i32 0
 // CHECK:STDOUT:   %4 = load i32, ptr %coerce.dive2, align 4
 // CHECK:STDOUT:   %call = call noundef zeroext i1 @_Zgt1AS_(i32 %3, i32 %4)
 // CHECK:STDOUT:   %storedv = zext i1 %call to i8
@@ -391,8 +391,8 @@ fn Driver(x: Cpp.A, y: Cpp.A) {
 // CHECK:STDOUT:   %x.addr = alloca ptr, align 8
 // CHECK:STDOUT:   %y.addr = alloca ptr, align 8
 // CHECK:STDOUT:   %return.addr = alloca ptr, align 8
-// CHECK:STDOUT:   %agg.tmp = alloca %struct.A, align 4
-// CHECK:STDOUT:   %agg.tmp1 = alloca %struct.A, align 4
+// CHECK:STDOUT:   %agg.tmp = alloca %struct.A.62, align 4
+// CHECK:STDOUT:   %agg.tmp1 = alloca %struct.A.62, align 4
 // CHECK:STDOUT:   store ptr %x, ptr %x.addr, align 8, !tbaa !21
 // CHECK:STDOUT:   store ptr %y, ptr %y.addr, align 8, !tbaa !21
 // CHECK:STDOUT:   store ptr %return, ptr %return.addr, align 8, !tbaa !24
@@ -401,9 +401,9 @@ fn Driver(x: Cpp.A, y: Cpp.A) {
 // CHECK:STDOUT:   call void @llvm.memcpy.p0.p0.i64(ptr align 4 %agg.tmp, ptr align 4 %1, i64 4, i1 false), !tbaa.struct !26
 // CHECK:STDOUT:   %2 = load ptr, ptr %y.addr, align 8, !tbaa !21
 // CHECK:STDOUT:   call void @llvm.memcpy.p0.p0.i64(ptr align 4 %agg.tmp1, ptr align 4 %2, i64 4, i1 false), !tbaa.struct !26
-// CHECK:STDOUT:   %coerce.dive = getelementptr inbounds nuw %struct.A, ptr %agg.tmp, i32 0, i32 0
+// CHECK:STDOUT:   %coerce.dive = getelementptr inbounds nuw %struct.A.62, ptr %agg.tmp, i32 0, i32 0
 // CHECK:STDOUT:   %3 = load i32, ptr %coerce.dive, align 4
-// CHECK:STDOUT:   %coerce.dive2 = getelementptr inbounds nuw %struct.A, ptr %agg.tmp1, i32 0, i32 0
+// CHECK:STDOUT:   %coerce.dive2 = getelementptr inbounds nuw %struct.A.62, ptr %agg.tmp1, i32 0, i32 0
 // CHECK:STDOUT:   %4 = load i32, ptr %coerce.dive2, align 4
 // CHECK:STDOUT:   %call = call noundef zeroext i1 @_Zge1AS_(i32 %3, i32 %4)
 // CHECK:STDOUT:   %storedv = zext i1 %call to i8
@@ -467,15 +467,15 @@ fn Driver(x: Cpp.A, y: Cpp.A) {
 // CHECK:STDOUT: ; Function Attrs: mustprogress nounwind uwtable
 // CHECK:STDOUT: define linkonce_odr dso_local noundef zeroext i1 @_Zlt1AS_(i32 %x.coerce, i32 %y.coerce) #4 comdat {
 // CHECK:STDOUT: entry:
-// CHECK:STDOUT:   %x = alloca %struct.A, align 4
-// CHECK:STDOUT:   %y = alloca %struct.A, align 4
-// CHECK:STDOUT:   %coerce.dive = getelementptr inbounds nuw %struct.A, ptr %x, i32 0, i32 0
+// CHECK:STDOUT:   %x = alloca %struct.A.62, align 4
+// CHECK:STDOUT:   %y = alloca %struct.A.62, align 4
+// CHECK:STDOUT:   %coerce.dive = getelementptr inbounds nuw %struct.A.62, ptr %x, i32 0, i32 0
 // CHECK:STDOUT:   store i32 %x.coerce, ptr %coerce.dive, align 4
-// CHECK:STDOUT:   %coerce.dive1 = getelementptr inbounds nuw %struct.A, ptr %y, i32 0, i32 0
+// CHECK:STDOUT:   %coerce.dive1 = getelementptr inbounds nuw %struct.A.62, ptr %y, i32 0, i32 0
 // CHECK:STDOUT:   store i32 %y.coerce, ptr %coerce.dive1, align 4
-// CHECK:STDOUT:   %value = getelementptr inbounds nuw %struct.A, ptr %x, i32 0, i32 0
+// CHECK:STDOUT:   %value = getelementptr inbounds nuw %struct.A.62, ptr %x, i32 0, i32 0
 // CHECK:STDOUT:   %0 = load i32, ptr %value, align 4, !tbaa !61
-// CHECK:STDOUT:   %value2 = getelementptr inbounds nuw %struct.A, ptr %y, i32 0, i32 0
+// CHECK:STDOUT:   %value2 = getelementptr inbounds nuw %struct.A.62, ptr %y, i32 0, i32 0
 // CHECK:STDOUT:   %1 = load i32, ptr %value2, align 4, !tbaa !61
 // CHECK:STDOUT:   %cmp = icmp slt i32 %0, %1
 // CHECK:STDOUT:   ret i1 %cmp
@@ -487,19 +487,19 @@ fn Driver(x: Cpp.A, y: Cpp.A) {
 // CHECK:STDOUT: ; Function Attrs: mustprogress nounwind uwtable
 // CHECK:STDOUT: define linkonce_odr dso_local noundef zeroext i1 @_Zle1AS_(i32 %x.coerce, i32 %y.coerce) #4 comdat {
 // CHECK:STDOUT: entry:
-// CHECK:STDOUT:   %x = alloca %struct.A, align 4
-// CHECK:STDOUT:   %y = alloca %struct.A, align 4
-// CHECK:STDOUT:   %agg.tmp = alloca %struct.A, align 4
-// CHECK:STDOUT:   %agg.tmp2 = alloca %struct.A, align 4
-// CHECK:STDOUT:   %coerce.dive = getelementptr inbounds nuw %struct.A, ptr %x, i32 0, i32 0
+// CHECK:STDOUT:   %x = alloca %struct.A.62, align 4
+// CHECK:STDOUT:   %y = alloca %struct.A.62, align 4
+// CHECK:STDOUT:   %agg.tmp = alloca %struct.A.62, align 4
+// CHECK:STDOUT:   %agg.tmp2 = alloca %struct.A.62, align 4
+// CHECK:STDOUT:   %coerce.dive = getelementptr inbounds nuw %struct.A.62, ptr %x, i32 0, i32 0
 // CHECK:STDOUT:   store i32 %x.coerce, ptr %coerce.dive, align 4
-// CHECK:STDOUT:   %coerce.dive1 = getelementptr inbounds nuw %struct.A, ptr %y, i32 0, i32 0
+// CHECK:STDOUT:   %coerce.dive1 = getelementptr inbounds nuw %struct.A.62, ptr %y, i32 0, i32 0
 // CHECK:STDOUT:   store i32 %y.coerce, ptr %coerce.dive1, align 4
 // CHECK:STDOUT:   call void @llvm.memcpy.p0.p0.i64(ptr align 4 %agg.tmp, ptr align 4 %y, i64 4, i1 false), !tbaa.struct !26
 // CHECK:STDOUT:   call void @llvm.memcpy.p0.p0.i64(ptr align 4 %agg.tmp2, ptr align 4 %x, i64 4, i1 false), !tbaa.struct !26
-// CHECK:STDOUT:   %coerce.dive3 = getelementptr inbounds nuw %struct.A, ptr %agg.tmp, i32 0, i32 0
+// CHECK:STDOUT:   %coerce.dive3 = getelementptr inbounds nuw %struct.A.62, ptr %agg.tmp, i32 0, i32 0
 // CHECK:STDOUT:   %0 = load i32, ptr %coerce.dive3, align 4
-// CHECK:STDOUT:   %coerce.dive4 = getelementptr inbounds nuw %struct.A, ptr %agg.tmp2, i32 0, i32 0
+// CHECK:STDOUT:   %coerce.dive4 = getelementptr inbounds nuw %struct.A.62, ptr %agg.tmp2, i32 0, i32 0
 // CHECK:STDOUT:   %1 = load i32, ptr %coerce.dive4, align 4
 // CHECK:STDOUT:   %call = call noundef zeroext i1 @_Zlt1AS_(i32 %0, i32 %1)
 // CHECK:STDOUT:   %lnot = xor i1 %call, true
@@ -509,19 +509,19 @@ fn Driver(x: Cpp.A, y: Cpp.A) {
 // CHECK:STDOUT: ; Function Attrs: mustprogress nounwind uwtable
 // CHECK:STDOUT: define linkonce_odr dso_local noundef zeroext i1 @_Zgt1AS_(i32 %x.coerce, i32 %y.coerce) #4 comdat {
 // CHECK:STDOUT: entry:
-// CHECK:STDOUT:   %x = alloca %struct.A, align 4
-// CHECK:STDOUT:   %y = alloca %struct.A, align 4
-// CHECK:STDOUT:   %agg.tmp = alloca %struct.A, align 4
-// CHECK:STDOUT:   %agg.tmp2 = alloca %struct.A, align 4
-// CHECK:STDOUT:   %coerce.dive = getelementptr inbounds nuw %struct.A, ptr %x, i32 0, i32 0
+// CHECK:STDOUT:   %x = alloca %struct.A.62, align 4
+// CHECK:STDOUT:   %y = alloca %struct.A.62, align 4
+// CHECK:STDOUT:   %agg.tmp = alloca %struct.A.62, align 4
+// CHECK:STDOUT:   %agg.tmp2 = alloca %struct.A.62, align 4
+// CHECK:STDOUT:   %coerce.dive = getelementptr inbounds nuw %struct.A.62, ptr %x, i32 0, i32 0
 // CHECK:STDOUT:   store i32 %x.coerce, ptr %coerce.dive, align 4
-// CHECK:STDOUT:   %coerce.dive1 = getelementptr inbounds nuw %struct.A, ptr %y, i32 0, i32 0
+// CHECK:STDOUT:   %coerce.dive1 = getelementptr inbounds nuw %struct.A.62, ptr %y, i32 0, i32 0
 // CHECK:STDOUT:   store i32 %y.coerce, ptr %coerce.dive1, align 4
 // CHECK:STDOUT:   call void @llvm.memcpy.p0.p0.i64(ptr align 4 %agg.tmp, ptr align 4 %y, i64 4, i1 false), !tbaa.struct !26
 // CHECK:STDOUT:   call void @llvm.memcpy.p0.p0.i64(ptr align 4 %agg.tmp2, ptr align 4 %x, i64 4, i1 false), !tbaa.struct !26
-// CHECK:STDOUT:   %coerce.dive3 = getelementptr inbounds nuw %struct.A, ptr %agg.tmp, i32 0, i32 0
+// CHECK:STDOUT:   %coerce.dive3 = getelementptr inbounds nuw %struct.A.62, ptr %agg.tmp, i32 0, i32 0
 // CHECK:STDOUT:   %0 = load i32, ptr %coerce.dive3, align 4
-// CHECK:STDOUT:   %coerce.dive4 = getelementptr inbounds nuw %struct.A, ptr %agg.tmp2, i32 0, i32 0
+// CHECK:STDOUT:   %coerce.dive4 = getelementptr inbounds nuw %struct.A.62, ptr %agg.tmp2, i32 0, i32 0
 // CHECK:STDOUT:   %1 = load i32, ptr %coerce.dive4, align 4
 // CHECK:STDOUT:   %call = call noundef zeroext i1 @_Zlt1AS_(i32 %0, i32 %1)
 // CHECK:STDOUT:   ret i1 %call
@@ -530,19 +530,19 @@ fn Driver(x: Cpp.A, y: Cpp.A) {
 // CHECK:STDOUT: ; Function Attrs: mustprogress nounwind uwtable
 // CHECK:STDOUT: define linkonce_odr dso_local noundef zeroext i1 @_Zge1AS_(i32 %x.coerce, i32 %y.coerce) #4 comdat {
 // CHECK:STDOUT: entry:
-// CHECK:STDOUT:   %x = alloca %struct.A, align 4
-// CHECK:STDOUT:   %y = alloca %struct.A, align 4
-// CHECK:STDOUT:   %agg.tmp = alloca %struct.A, align 4
-// CHECK:STDOUT:   %agg.tmp2 = alloca %struct.A, align 4
-// CHECK:STDOUT:   %coerce.dive = getelementptr inbounds nuw %struct.A, ptr %x, i32 0, i32 0
+// CHECK:STDOUT:   %x = alloca %struct.A.62, align 4
+// CHECK:STDOUT:   %y = alloca %struct.A.62, align 4
+// CHECK:STDOUT:   %agg.tmp = alloca %struct.A.62, align 4
+// CHECK:STDOUT:   %agg.tmp2 = alloca %struct.A.62, align 4
+// CHECK:STDOUT:   %coerce.dive = getelementptr inbounds nuw %struct.A.62, ptr %x, i32 0, i32 0
 // CHECK:STDOUT:   store i32 %x.coerce, ptr %coerce.dive, align 4
-// CHECK:STDOUT:   %coerce.dive1 = getelementptr inbounds nuw %struct.A, ptr %y, i32 0, i32 0
+// CHECK:STDOUT:   %coerce.dive1 = getelementptr inbounds nuw %struct.A.62, ptr %y, i32 0, i32 0
 // CHECK:STDOUT:   store i32 %y.coerce, ptr %coerce.dive1, align 4
 // CHECK:STDOUT:   call void @llvm.memcpy.p0.p0.i64(ptr align 4 %agg.tmp, ptr align 4 %x, i64 4, i1 false), !tbaa.struct !26
 // CHECK:STDOUT:   call void @llvm.memcpy.p0.p0.i64(ptr align 4 %agg.tmp2, ptr align 4 %y, i64 4, i1 false), !tbaa.struct !26
-// CHECK:STDOUT:   %coerce.dive3 = getelementptr inbounds nuw %struct.A, ptr %agg.tmp, i32 0, i32 0
+// CHECK:STDOUT:   %coerce.dive3 = getelementptr inbounds nuw %struct.A.62, ptr %agg.tmp, i32 0, i32 0
 // CHECK:STDOUT:   %0 = load i32, ptr %coerce.dive3, align 4
-// CHECK:STDOUT:   %coerce.dive4 = getelementptr inbounds nuw %struct.A, ptr %agg.tmp2, i32 0, i32 0
+// CHECK:STDOUT:   %coerce.dive4 = getelementptr inbounds nuw %struct.A.62, ptr %agg.tmp2, i32 0, i32 0
 // CHECK:STDOUT:   %1 = load i32, ptr %coerce.dive4, align 4
 // CHECK:STDOUT:   %call = call noundef zeroext i1 @_Zlt1AS_(i32 %0, i32 %1)
 // CHECK:STDOUT:   %lnot = xor i1 %call, true
diff --git a/toolchain/lower/testdata/interop/cpp/reference.carbon b/toolchain/lower/testdata/interop/cpp/reference.carbon
index 0527ddcd7764..b195c43b3b60 100644
--- a/toolchain/lower/testdata/interop/cpp/reference.carbon
+++ b/toolchain/lower/testdata/interop/cpp/reference.carbon
@@ -599,7 +599,7 @@ fn GetRefs() {
 // CHECK:STDOUT: target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
 // CHECK:STDOUT: target triple = "x86_64-unknown-linux-gnu"
 // CHECK:STDOUT:
-// CHECK:STDOUT: %class.ForceThunk = type { i8 }
+// CHECK:STDOUT: %class.ForceThunk.23 = type { i8 }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
 // CHECK:STDOUT: define void @_CGetRefs.Main() #0 !dbg !12 {
@@ -616,7 +616,7 @@ fn GetRefs() {
 // CHECK:STDOUT: ; Function Attrs: alwaysinline mustprogress uwtable
 // CHECK:STDOUT: define internal noundef nonnull align 1 dereferenceable(1) ptr @_Z10ReturnCRef10ForceThunk.carbon_thunk.() #1 {
 // CHECK:STDOUT: entry:
-// CHECK:STDOUT:   %agg.tmp = alloca %class.ForceThunk, align 1
+// CHECK:STDOUT:   %agg.tmp = alloca %class.ForceThunk.23, align 1
 // CHECK:STDOUT:   %call = call noundef nonnull align 1 dereferenceable(1) ptr @_Z10ReturnCRef10ForceThunk()
 // CHECK:STDOUT:   ret ptr %call
 // CHECK:STDOUT: }
@@ -624,7 +624,7 @@ fn GetRefs() {
 // CHECK:STDOUT: ; Function Attrs: alwaysinline mustprogress uwtable
 // CHECK:STDOUT: define internal noundef nonnull align 1 dereferenceable(1) ptr @_Z11ReturnCRRef10ForceThunk.carbon_thunk.() #1 {
 // CHECK:STDOUT: entry:
-// CHECK:STDOUT:   %agg.tmp = alloca %class.ForceThunk, align 1
+// CHECK:STDOUT:   %agg.tmp = alloca %class.ForceThunk.23, align 1
 // CHECK:STDOUT:   %call = call noundef nonnull align 1 dereferenceable(1) ptr @_Z11ReturnCRRef10ForceThunk()
 // CHECK:STDOUT:   ret ptr %call
 // CHECK:STDOUT: }
@@ -632,7 +632,7 @@ fn GetRefs() {
 // CHECK:STDOUT: ; Function Attrs: alwaysinline mustprogress uwtable
 // CHECK:STDOUT: define internal noundef nonnull align 1 dereferenceable(1) ptr @_Z15ReturnConstCRef10ForceThunk.carbon_thunk.() #1 {
 // CHECK:STDOUT: entry:
-// CHECK:STDOUT:   %agg.tmp = alloca %class.ForceThunk, align 1
+// CHECK:STDOUT:   %agg.tmp = alloca %class.ForceThunk.23, align 1
 // CHECK:STDOUT:   %call = call noundef nonnull align 1 dereferenceable(1) ptr @_Z15ReturnConstCRef10ForceThunk()
 // CHECK:STDOUT:   ret ptr %call
 // CHECK:STDOUT: }
@@ -640,7 +640,7 @@ fn GetRefs() {
 // CHECK:STDOUT: ; Function Attrs: alwaysinline mustprogress uwtable
 // CHECK:STDOUT: define internal noundef nonnull align 4 dereferenceable(4) ptr @_Z12ReturnIntRef10ForceThunk.carbon_thunk.() #1 {
 // CHECK:STDOUT: entry:
-// CHECK:STDOUT:   %agg.tmp = alloca %class.ForceThunk, align 1
+// CHECK:STDOUT:   %agg.tmp = alloca %class.ForceThunk.23, align 1
 // CHECK:STDOUT:   %call = call noundef nonnull align 4 dereferenceable(4) ptr @_Z12ReturnIntRef10ForceThunk()
 // CHECK:STDOUT:   ret ptr %call
 // CHECK:STDOUT: }
@@ -648,7 +648,7 @@ fn GetRefs() {
 // CHECK:STDOUT: ; Function Attrs: alwaysinline mustprogress uwtable
 // CHECK:STDOUT: define internal noundef nonnull align 4 dereferenceable(4) ptr @_Z13ReturnIntRRef10ForceThunk.carbon_thunk.() #1 {
 // CHECK:STDOUT: entry:
-// CHECK:STDOUT:   %agg.tmp = alloca %class.ForceThunk, align 1
+// CHECK:STDOUT:   %agg.tmp = alloca %class.ForceThunk.23, align 1
 // CHECK:STDOUT:   %call = call noundef nonnull align 4 dereferenceable(4) ptr @_Z13ReturnIntRRef10ForceThunk()
 // CHECK:STDOUT:   ret ptr %call
 // CHECK:STDOUT: }
@@ -656,7 +656,7 @@ fn GetRefs() {
 // CHECK:STDOUT: ; Function Attrs: alwaysinline mustprogress uwtable
 // CHECK:STDOUT: define internal noundef nonnull align 4 dereferenceable(4) ptr @_Z17ReturnConstIntRef10ForceThunk.carbon_thunk.() #1 {
 // CHECK:STDOUT: entry:
-// CHECK:STDOUT:   %agg.tmp = alloca %class.ForceThunk, align 1
+// CHECK:STDOUT:   %agg.tmp = alloca %class.ForceThunk.23, align 1
 // CHECK:STDOUT:   %call = call noundef nonnull align 4 dereferenceable(4) ptr @_Z17ReturnConstIntRef10ForceThunk()
 // CHECK:STDOUT:   ret ptr %call
 // CHECK:STDOUT: }
diff --git a/toolchain/lower/testdata/interop/cpp/share_ast.carbon b/toolchain/lower/testdata/interop/cpp/share_ast.carbon
new file mode 100644
index 000000000000..a0505dc25f11
--- /dev/null
+++ b/toolchain/lower/testdata/interop/cpp/share_ast.carbon
@@ -0,0 +1,364 @@
+// 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/primitives.carbon
+// EXTRA-ARGS: --share-cpp-ast
+//
+// AUTOUPDATE
+// TIP: To test this file alone, run:
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/lower/testdata/interop/cpp/share_ast.carbon
+// TIP: To dump output, run:
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/interop/cpp/share_ast.carbon
+
+// --- a.h
+#ifndef A_H
+#define A_H
+struct A {
+  int a, b;
+};
+inline A make_a() { return {1, 2}; }
+#endif
+
+// --- b.h
+#ifndef B_H
+#define B_H
+struct B {
+  int x, y;
+};
+inline B make_b() { return {3, 4}; }
+#endif
+
+// --- use_a.carbon
+library "[[@TEST_NAME]]";
+import Cpp library "a.h";
+
+fn Test() -> i32 {
+  var a: Cpp.A = Cpp.make_a();
+  return a.b;
+}
+
+// --- use_b.carbon
+library "[[@TEST_NAME]]";
+import Cpp library "b.h";
+
+fn Test() -> i32 {
+  var b: Cpp.B = Cpp.make_b();
+  return b.x;
+}
+
+// --- use_both.carbon
+library "[[@TEST_NAME]]";
+import Cpp library "a.h";
+import Cpp library "b.h";
+
+fn TestA() -> i32 {
+  var a: Cpp.A = Cpp.make_a();
+  return a.b;
+}
+
+fn TestB() -> i32 {
+  var b: Cpp.B = Cpp.make_b();
+  return b.x;
+}
+
+
+// CHECK:STDOUT: ; ---
+// CHECK:STDOUT: ; ModuleID = 'use_a.carbon'
+// CHECK:STDOUT: source_filename = "use_a.carbon"
+// CHECK:STDOUT: target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
+// CHECK:STDOUT: target triple = "x86_64-unknown-linux-gnu"
+// CHECK:STDOUT:
+// CHECK:STDOUT: %struct.A = type { i32, i32 }
+// CHECK:STDOUT:
+// CHECK:STDOUT: $_Z6make_av = comdat any
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nounwind
+// CHECK:STDOUT: define i32 @_CTest.Main() #0 !dbg !12 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %a.var = alloca [8 x i8], align 4, !dbg !16
+// CHECK:STDOUT:   call void @llvm.lifetime.start.p0(ptr %a.var), !dbg !16
+// CHECK:STDOUT:   call void @_Z6make_av.carbon_thunk.(ptr %a.var), !dbg !17
+// CHECK:STDOUT:   %.loc6_11.1.b = getelementptr inbounds nuw [8 x i8], ptr %a.var, i32 0, i32 4, !dbg !18
+// CHECK:STDOUT:   %.loc6_11.2 = load i32, ptr %.loc6_11.1.b, align 4, !dbg !18
+// CHECK:STDOUT:   ret i32 %.loc6_11.2, !dbg !19
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: alwaysinline mustprogress uwtable
+// CHECK:STDOUT: define internal void @_Z6make_av.carbon_thunk.(ptr noundef %return) #1 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %return.addr = alloca ptr, align 8
+// CHECK:STDOUT:   store ptr %return, ptr %return.addr, align 8, !tbaa !20
+// CHECK:STDOUT:   %0 = load ptr, ptr %return.addr, align 8, !tbaa !20
+// CHECK:STDOUT:   %call = call i64 @_Z6make_av()
+// CHECK:STDOUT:   store i64 %call, ptr %0, align 4
+// CHECK:STDOUT:   ret void
+// 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)) #2
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: inlinehint mustprogress nounwind uwtable
+// CHECK:STDOUT: define linkonce_odr dso_local i64 @_Z6make_av() #3 comdat {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %retval = alloca %struct.A, align 4
+// CHECK:STDOUT:   %a = getelementptr inbounds nuw %struct.A, ptr %retval, i32 0, i32 0
+// CHECK:STDOUT:   store i32 1, ptr %a, align 4, !tbaa !23
+// CHECK:STDOUT:   %b = getelementptr inbounds nuw %struct.A, ptr %retval, i32 0, i32 1
+// CHECK:STDOUT:   store i32 2, ptr %b, align 4, !tbaa !25
+// CHECK:STDOUT:   %0 = load i64, ptr %retval, align 4
+// CHECK:STDOUT:   ret i64 %0
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: attributes #0 = { nounwind }
+// CHECK:STDOUT: attributes #1 = { alwaysinline mustprogress uwtable "min-legal-vector-width"="0" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cmov,+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" }
+// CHECK:STDOUT: attributes #2 = { nocallback nofree nosync nounwind willreturn memory(argmem: readwrite) }
+// CHECK:STDOUT: attributes #3 = { inlinehint mustprogress nounwind uwtable "min-legal-vector-width"="0" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cmov,+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" }
+// CHECK:STDOUT:
+// CHECK:STDOUT: !llvm.dbg.cu = !{!0}
+// CHECK:STDOUT: !llvm.module.flags = !{!2, !3, !4, !5, !6}
+// CHECK:STDOUT: !llvm.errno.tbaa = !{!7}
+// CHECK:STDOUT:
+// CHECK:STDOUT: !0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "carbon", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug)
+// CHECK:STDOUT: !1 = !DIFile(filename: "use_a.carbon", directory: "")
+// CHECK:STDOUT: !2 = !{i32 8, !"PIC Level", i32 2}
+// CHECK:STDOUT: !3 = !{i32 7, !"PIE Level", i32 2}
+// CHECK:STDOUT: !4 = !{i32 7, !"uwtable", i32 2}
+// CHECK:STDOUT: !5 = !{i32 7, !"Dwarf Version", i32 5}
+// CHECK:STDOUT: !6 = !{i32 2, !"Debug Info Version", i32 3}
+// CHECK:STDOUT: !7 = !{!8, !9, i64 0}
+// CHECK:STDOUT: !8 = !{!"__libc_errno", !9, i64 0}
+// CHECK:STDOUT: !9 = !{!"int", !10, i64 0}
+// CHECK:STDOUT: !10 = !{!"omnipotent char", !11, i64 0}
+// CHECK:STDOUT: !11 = !{!"Simple C++ TBAA"}
+// CHECK:STDOUT: !12 = distinct !DISubprogram(name: "Test", linkageName: "_CTest.Main", scope: null, file: !1, line: 4, type: !13, spFlags: DISPFlagDefinition, unit: !0)
+// CHECK:STDOUT: !13 = !DISubroutineType(types: !14)
+// CHECK:STDOUT: !14 = !{!15}
+// CHECK:STDOUT: !15 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+// CHECK:STDOUT: !16 = !DILocation(line: 5, column: 3, scope: !12)
+// CHECK:STDOUT: !17 = !DILocation(line: 5, column: 18, scope: !12)
+// CHECK:STDOUT: !18 = !DILocation(line: 6, column: 10, scope: !12)
+// CHECK:STDOUT: !19 = !DILocation(line: 6, column: 3, scope: !12)
+// CHECK:STDOUT: !20 = !{!21, !21, i64 0}
+// CHECK:STDOUT: !21 = !{!"p1 _ZTS1A", !22, i64 0}
+// CHECK:STDOUT: !22 = !{!"any pointer", !10, i64 0}
+// CHECK:STDOUT: !23 = !{!24, !9, i64 0}
+// CHECK:STDOUT: !24 = !{!"_ZTS1A", !9, i64 0, !9, i64 4}
+// CHECK:STDOUT: !25 = !{!24, !9, i64 4}
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; ---
+// CHECK:STDOUT: ; ModuleID = 'use_b.carbon'
+// CHECK:STDOUT: source_filename = "use_b.carbon"
+// CHECK:STDOUT: target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
+// CHECK:STDOUT: target triple = "x86_64-unknown-linux-gnu"
+// CHECK:STDOUT:
+// CHECK:STDOUT: %struct.B = type { i32, i32 }
+// CHECK:STDOUT:
+// CHECK:STDOUT: $_Z6make_bv = comdat any
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nounwind
+// CHECK:STDOUT: define i32 @_CTest.Main() #0 !dbg !12 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %b.var = alloca [8 x i8], align 4, !dbg !16
+// CHECK:STDOUT:   call void @llvm.lifetime.start.p0(ptr %b.var), !dbg !16
+// CHECK:STDOUT:   call void @_Z6make_bv.carbon_thunk.(ptr %b.var), !dbg !17
+// CHECK:STDOUT:   %.loc6_11.1.x = getelementptr inbounds nuw [8 x i8], ptr %b.var, i32 0, i32 0, !dbg !18
+// CHECK:STDOUT:   %.loc6_11.2 = load i32, ptr %.loc6_11.1.x, align 4, !dbg !18
+// CHECK:STDOUT:   ret i32 %.loc6_11.2, !dbg !19
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: alwaysinline mustprogress uwtable
+// CHECK:STDOUT: define internal void @_Z6make_bv.carbon_thunk.(ptr noundef %return) #1 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %return.addr = alloca ptr, align 8
+// CHECK:STDOUT:   store ptr %return, ptr %return.addr, align 8, !tbaa !20
+// CHECK:STDOUT:   %0 = load ptr, ptr %return.addr, align 8, !tbaa !20
+// CHECK:STDOUT:   %call = call i64 @_Z6make_bv()
+// CHECK:STDOUT:   store i64 %call, ptr %0, align 4
+// CHECK:STDOUT:   ret void
+// 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)) #2
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: inlinehint mustprogress nounwind uwtable
+// CHECK:STDOUT: define linkonce_odr dso_local i64 @_Z6make_bv() #3 comdat {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %retval = alloca %struct.B, align 4
+// CHECK:STDOUT:   %x = getelementptr inbounds nuw %struct.B, ptr %retval, i32 0, i32 0
+// CHECK:STDOUT:   store i32 3, ptr %x, align 4, !tbaa !23
+// CHECK:STDOUT:   %y = getelementptr inbounds nuw %struct.B, ptr %retval, i32 0, i32 1
+// CHECK:STDOUT:   store i32 4, ptr %y, align 4, !tbaa !25
+// CHECK:STDOUT:   %0 = load i64, ptr %retval, align 4
+// CHECK:STDOUT:   ret i64 %0
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: attributes #0 = { nounwind }
+// CHECK:STDOUT: attributes #1 = { alwaysinline mustprogress uwtable "min-legal-vector-width"="0" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cmov,+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" }
+// CHECK:STDOUT: attributes #2 = { nocallback nofree nosync nounwind willreturn memory(argmem: readwrite) }
+// CHECK:STDOUT: attributes #3 = { inlinehint mustprogress nounwind uwtable "min-legal-vector-width"="0" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cmov,+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" }
+// CHECK:STDOUT:
+// CHECK:STDOUT: !llvm.dbg.cu = !{!0}
+// CHECK:STDOUT: !llvm.module.flags = !{!2, !3, !4, !5, !6}
+// CHECK:STDOUT: !llvm.errno.tbaa = !{!7}
+// CHECK:STDOUT:
+// CHECK:STDOUT: !0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "carbon", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug)
+// CHECK:STDOUT: !1 = !DIFile(filename: "use_b.carbon", directory: "")
+// CHECK:STDOUT: !2 = !{i32 8, !"PIC Level", i32 2}
+// CHECK:STDOUT: !3 = !{i32 7, !"PIE Level", i32 2}
+// CHECK:STDOUT: !4 = !{i32 7, !"uwtable", i32 2}
+// CHECK:STDOUT: !5 = !{i32 7, !"Dwarf Version", i32 5}
+// CHECK:STDOUT: !6 = !{i32 2, !"Debug Info Version", i32 3}
+// CHECK:STDOUT: !7 = !{!8, !9, i64 0}
+// CHECK:STDOUT: !8 = !{!"__libc_errno", !9, i64 0}
+// CHECK:STDOUT: !9 = !{!"int", !10, i64 0}
+// CHECK:STDOUT: !10 = !{!"omnipotent char", !11, i64 0}
+// CHECK:STDOUT: !11 = !{!"Simple C++ TBAA"}
+// CHECK:STDOUT: !12 = distinct !DISubprogram(name: "Test", linkageName: "_CTest.Main", scope: null, file: !1, line: 4, type: !13, spFlags: DISPFlagDefinition, unit: !0)
+// CHECK:STDOUT: !13 = !DISubroutineType(types: !14)
+// CHECK:STDOUT: !14 = !{!15}
+// CHECK:STDOUT: !15 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+// CHECK:STDOUT: !16 = !DILocation(line: 5, column: 3, scope: !12)
+// CHECK:STDOUT: !17 = !DILocation(line: 5, column: 18, scope: !12)
+// CHECK:STDOUT: !18 = !DILocation(line: 6, column: 10, scope: !12)
+// CHECK:STDOUT: !19 = !DILocation(line: 6, column: 3, scope: !12)
+// CHECK:STDOUT: !20 = !{!21, !21, i64 0}
+// CHECK:STDOUT: !21 = !{!"p1 _ZTS1B", !22, i64 0}
+// CHECK:STDOUT: !22 = !{!"any pointer", !10, i64 0}
+// CHECK:STDOUT: !23 = !{!24, !9, i64 0}
+// CHECK:STDOUT: !24 = !{!"_ZTS1B", !9, i64 0, !9, i64 4}
+// CHECK:STDOUT: !25 = !{!24, !9, i64 4}
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; ---
+// CHECK:STDOUT: ; ModuleID = 'use_both.carbon'
+// CHECK:STDOUT: source_filename = "use_both.carbon"
+// CHECK:STDOUT: target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
+// CHECK:STDOUT: target triple = "x86_64-unknown-linux-gnu"
+// CHECK:STDOUT:
+// CHECK:STDOUT: %struct.A.32 = type { i32, i32 }
+// CHECK:STDOUT: %struct.B.33 = type { i32, i32 }
+// CHECK:STDOUT:
+// CHECK:STDOUT: $_Z6make_av = comdat any
+// CHECK:STDOUT:
+// CHECK:STDOUT: $_Z6make_bv = comdat any
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nounwind
+// CHECK:STDOUT: define i32 @_CTestA.Main() #0 !dbg !12 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %a.var = alloca [8 x i8], align 4, !dbg !16
+// CHECK:STDOUT:   call void @llvm.lifetime.start.p0(ptr %a.var), !dbg !16
+// CHECK:STDOUT:   call void @_Z6make_av.carbon_thunk.(ptr %a.var), !dbg !17
+// CHECK:STDOUT:   %.loc7_11.1.b = getelementptr inbounds nuw [8 x i8], ptr %a.var, i32 0, i32 4, !dbg !18
+// CHECK:STDOUT:   %.loc7_11.2 = load i32, ptr %.loc7_11.1.b, align 4, !dbg !18
+// CHECK:STDOUT:   ret i32 %.loc7_11.2, !dbg !19
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: alwaysinline mustprogress uwtable
+// CHECK:STDOUT: define internal void @_Z6make_av.carbon_thunk.(ptr noundef %return) #1 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %return.addr = alloca ptr, align 8
+// CHECK:STDOUT:   store ptr %return, ptr %return.addr, align 8, !tbaa !20
+// CHECK:STDOUT:   %0 = load ptr, ptr %return.addr, align 8, !tbaa !20
+// CHECK:STDOUT:   %call = call i64 @_Z6make_av()
+// CHECK:STDOUT:   store i64 %call, ptr %0, align 4
+// CHECK:STDOUT:   ret void
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nounwind
+// CHECK:STDOUT: define i32 @_CTestB.Main() #0 !dbg !23 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %b.var = alloca [8 x i8], align 4, !dbg !24
+// CHECK:STDOUT:   call void @llvm.lifetime.start.p0(ptr %b.var), !dbg !24
+// CHECK:STDOUT:   call void @_Z6make_bv.carbon_thunk.(ptr %b.var), !dbg !25
+// CHECK:STDOUT:   %.loc12_11.1.x = getelementptr inbounds nuw [8 x i8], ptr %b.var, i32 0, i32 0, !dbg !26
+// CHECK:STDOUT:   %.loc12_11.2 = load i32, ptr %.loc12_11.1.x, align 4, !dbg !26
+// CHECK:STDOUT:   ret i32 %.loc12_11.2, !dbg !27
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: alwaysinline mustprogress uwtable
+// CHECK:STDOUT: define internal void @_Z6make_bv.carbon_thunk.(ptr noundef %return) #1 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %return.addr = alloca ptr, align 8
+// CHECK:STDOUT:   store ptr %return, ptr %return.addr, align 8, !tbaa !28
+// CHECK:STDOUT:   %0 = load ptr, ptr %return.addr, align 8, !tbaa !28
+// CHECK:STDOUT:   %call = call i64 @_Z6make_bv()
+// CHECK:STDOUT:   store i64 %call, ptr %0, align 4
+// CHECK:STDOUT:   ret void
+// 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)) #2
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: inlinehint mustprogress nounwind uwtable
+// CHECK:STDOUT: define linkonce_odr dso_local i64 @_Z6make_av() #3 comdat {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %retval = alloca %struct.A.32, align 4
+// CHECK:STDOUT:   %a = getelementptr inbounds nuw %struct.A.32, ptr %retval, i32 0, i32 0
+// CHECK:STDOUT:   store i32 1, ptr %a, align 4, !tbaa !30
+// CHECK:STDOUT:   %b = getelementptr inbounds nuw %struct.A.32, ptr %retval, i32 0, i32 1
+// CHECK:STDOUT:   store i32 2, ptr %b, align 4, !tbaa !32
+// CHECK:STDOUT:   %0 = load i64, ptr %retval, align 4
+// CHECK:STDOUT:   ret i64 %0
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: inlinehint mustprogress nounwind uwtable
+// CHECK:STDOUT: define linkonce_odr dso_local i64 @_Z6make_bv() #3 comdat {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %retval = alloca %struct.B.33, align 4
+// CHECK:STDOUT:   %x = getelementptr inbounds nuw %struct.B.33, ptr %retval, i32 0, i32 0
+// CHECK:STDOUT:   store i32 3, ptr %x, align 4, !tbaa !33
+// CHECK:STDOUT:   %y = getelementptr inbounds nuw %struct.B.33, ptr %retval, i32 0, i32 1
+// CHECK:STDOUT:   store i32 4, ptr %y, align 4, !tbaa !35
+// CHECK:STDOUT:   %0 = load i64, ptr %retval, align 4
+// CHECK:STDOUT:   ret i64 %0
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; uselistorder directives
+// CHECK:STDOUT: uselistorder ptr @llvm.lifetime.start.p0, { 1, 0 }
+// CHECK:STDOUT:
+// CHECK:STDOUT: attributes #0 = { nounwind }
+// CHECK:STDOUT: attributes #1 = { alwaysinline mustprogress uwtable "min-legal-vector-width"="0" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cmov,+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" }
+// CHECK:STDOUT: attributes #2 = { nocallback nofree nosync nounwind willreturn memory(argmem: readwrite) }
+// CHECK:STDOUT: attributes #3 = { inlinehint mustprogress nounwind uwtable "min-legal-vector-width"="0" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cmov,+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" }
+// CHECK:STDOUT:
+// CHECK:STDOUT: !llvm.dbg.cu = !{!0}
+// CHECK:STDOUT: !llvm.module.flags = !{!2, !3, !4, !5, !6}
+// CHECK:STDOUT: !llvm.errno.tbaa = !{!7}
+// CHECK:STDOUT:
+// CHECK:STDOUT: !0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "carbon", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug)
+// CHECK:STDOUT: !1 = !DIFile(filename: "use_both.carbon", directory: "")
+// CHECK:STDOUT: !2 = !{i32 8, !"PIC Level", i32 2}
+// CHECK:STDOUT: !3 = !{i32 7, !"PIE Level", i32 2}
+// CHECK:STDOUT: !4 = !{i32 7, !"uwtable", i32 2}
+// CHECK:STDOUT: !5 = !{i32 7, !"Dwarf Version", i32 5}
+// CHECK:STDOUT: !6 = !{i32 2, !"Debug Info Version", i32 3}
+// CHECK:STDOUT: !7 = !{!8, !9, i64 0}
+// CHECK:STDOUT: !8 = !{!"__libc_errno", !9, i64 0}
+// CHECK:STDOUT: !9 = !{!"int", !10, i64 0}
+// CHECK:STDOUT: !10 = !{!"omnipotent char", !11, i64 0}
+// CHECK:STDOUT: !11 = !{!"Simple C++ TBAA"}
+// CHECK:STDOUT: !12 = distinct !DISubprogram(name: "TestA", linkageName: "_CTestA.Main", scope: null, file: !1, line: 5, type: !13, spFlags: DISPFlagDefinition, unit: !0)
+// CHECK:STDOUT: !13 = !DISubroutineType(types: !14)
+// CHECK:STDOUT: !14 = !{!15}
+// CHECK:STDOUT: !15 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+// CHECK:STDOUT: !16 = !DILocation(line: 6, column: 3, scope: !12)
+// CHECK:STDOUT: !17 = !DILocation(line: 6, column: 18, scope: !12)
+// CHECK:STDOUT: !18 = !DILocation(line: 7, column: 10, scope: !12)
+// CHECK:STDOUT: !19 = !DILocation(line: 7, column: 3, scope: !12)
+// CHECK:STDOUT: !20 = !{!21, !21, i64 0}
+// CHECK:STDOUT: !21 = !{!"p1 _ZTS1A", !22, i64 0}
+// CHECK:STDOUT: !22 = !{!"any pointer", !10, i64 0}
+// CHECK:STDOUT: !23 = distinct !DISubprogram(name: "TestB", linkageName: "_CTestB.Main", scope: null, file: !1, line: 10, type: !13, spFlags: DISPFlagDefinition, unit: !0)
+// CHECK:STDOUT: !24 = !DILocation(line: 11, column: 3, scope: !23)
+// CHECK:STDOUT: !25 = !DILocation(line: 11, column: 18, scope: !23)
+// CHECK:STDOUT: !26 = !DILocation(line: 12, column: 10, scope: !23)
+// CHECK:STDOUT: !27 = !DILocation(line: 12, column: 3, scope: !23)
+// CHECK:STDOUT: !28 = !{!29, !29, i64 0}
+// CHECK:STDOUT: !29 = !{!"p1 _ZTS1B", !22, i64 0}
+// CHECK:STDOUT: !30 = !{!31, !9, i64 0}
+// CHECK:STDOUT: !31 = !{!"_ZTS1A", !9, i64 0, !9, i64 4}
+// CHECK:STDOUT: !32 = !{!31, !9, i64 4}
+// CHECK:STDOUT: !33 = !{!34, !9, i64 0}
+// CHECK:STDOUT: !34 = !{!"_ZTS1B", !9, i64 0, !9, i64 4}
+// CHECK:STDOUT: !35 = !{!34, !9, i64 4}
+// CHECK:STDOUT:
diff --git a/toolchain/lower/testdata/interop/cpp/std_initializer_list.carbon b/toolchain/lower/testdata/interop/cpp/std_initializer_list.carbon
index 11571025a4ef..dd0d76773517 100644
--- a/toolchain/lower/testdata/interop/cpp/std_initializer_list.carbon
+++ b/toolchain/lower/testdata/interop/cpp/std_initializer_list.carbon
@@ -368,7 +368,7 @@ fn InitNontrivialDtor() {
 // CHECK:STDOUT: target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
 // CHECK:STDOUT: target triple = "x86_64-unknown-linux-gnu"
 // CHECK:STDOUT:
-// CHECK:STDOUT: %"class.std::initializer_list" = type { ptr, i64 }
+// CHECK:STDOUT: %"class.std::initializer_list.64" = type { ptr, i64 }
 // CHECK:STDOUT:
 // CHECK:STDOUT: $_ZN11vector_likeD2Ev = comdat any
 // CHECK:STDOUT:
@@ -442,7 +442,7 @@ fn InitNontrivialDtor() {
 // CHECK:STDOUT: entry:
 // CHECK:STDOUT:   %list.addr = alloca ptr, align 8
 // CHECK:STDOUT:   %return.addr = alloca ptr, align 8
-// CHECK:STDOUT:   %agg.tmp = alloca %"class.std::initializer_list", align 8
+// CHECK:STDOUT:   %agg.tmp = alloca %"class.std::initializer_list.64", align 8
 // CHECK:STDOUT:   store ptr %list, ptr %list.addr, align 8, !tbaa !38
 // CHECK:STDOUT:   store ptr %return, ptr %return.addr, align 8, !tbaa !41
 // CHECK:STDOUT:   %0 = load ptr, ptr %return.addr, align 8, !tbaa !41
@@ -521,7 +521,7 @@ fn InitNontrivialDtor() {
 // CHECK:STDOUT: ; Function Attrs: mustprogress nounwind uwtable
 // CHECK:STDOUT: define linkonce_odr dso_local void @_ZN11vector_likeC2ESt16initializer_listIiE(ptr noundef nonnull align 1 dereferenceable(1) %this, ptr %list.coerce0, i64 %list.coerce1) unnamed_addr #2 comdat align 2 {
 // CHECK:STDOUT: entry:
-// CHECK:STDOUT:   %list = alloca %"class.std::initializer_list", align 8
+// CHECK:STDOUT:   %list = alloca %"class.std::initializer_list.64", align 8
 // CHECK:STDOUT:   %this.addr = alloca ptr, align 8
 // CHECK:STDOUT:   %0 = getelementptr inbounds nuw { ptr, i64 }, ptr %list, i32 0, i32 0
 // CHECK:STDOUT:   store ptr %list.coerce0, ptr %0, align 8
diff --git a/toolchain/lower/testdata/primitives/type_values.carbon b/toolchain/lower/testdata/primitives/type_values.carbon
index e689b5e65744..e9be58a34b96 100644
--- a/toolchain/lower/testdata/primitives/type_values.carbon
+++ b/toolchain/lower/testdata/primitives/type_values.carbon
@@ -29,24 +29,24 @@ fn F64() -> type {
 // CHECK:STDOUT: ; ModuleID = 'type_values.carbon'
 // CHECK:STDOUT: source_filename = "type_values.carbon"
 // CHECK:STDOUT:
-// CHECK:STDOUT: %type = type {}
+// CHECK:STDOUT: %type.26 = type {}
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define %type @_CI32.Main() #0 !dbg !4 {
+// CHECK:STDOUT: define %type.26 @_CI32.Main() #0 !dbg !4 {
 // CHECK:STDOUT: entry:
-// CHECK:STDOUT:   ret %type zeroinitializer, !dbg !8
+// CHECK:STDOUT:   ret %type.26 zeroinitializer, !dbg !8
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define %type @_CI48.Main() #0 !dbg !9 {
+// CHECK:STDOUT: define %type.26 @_CI48.Main() #0 !dbg !9 {
 // CHECK:STDOUT: entry:
-// CHECK:STDOUT:   ret %type zeroinitializer, !dbg !10
+// CHECK:STDOUT:   ret %type.26 zeroinitializer, !dbg !10
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: ; Function Attrs: nounwind
-// CHECK:STDOUT: define %type @_CF64.Main() #0 !dbg !11 {
+// CHECK:STDOUT: define %type.26 @_CF64.Main() #0 !dbg !11 {
 // CHECK:STDOUT: entry:
-// CHECK:STDOUT:   ret %type zeroinitializer, !dbg !12
+// CHECK:STDOUT:   ret %type.26 zeroinitializer, !dbg !12
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: attributes #0 = { nounwind }
diff --git a/toolchain/sem_ir/cpp_file.cpp b/toolchain/sem_ir/cpp_file.cpp
index f7e97a3d50c6..dabbfcc62b6c 100644
--- a/toolchain/sem_ir/cpp_file.cpp
+++ b/toolchain/sem_ir/cpp_file.cpp
@@ -12,8 +12,13 @@
 namespace Carbon::SemIR {
 
 CppFile::CppFile(std::shared_ptr<clang::CompilerInstance> clang,
-                 llvm::LLVMContext* llvm_context)
-    : clang_(std::move(clang)), llvm_context_(llvm_context) {}
+                 std::unique_ptr<clang::MangleContext> mangle_context,
+                 llvm::LLVMContext* llvm_context,
+                 clang::CodeGenerator* code_generator)
+    : clang_(std::move(clang)),
+      mangle_context_(std::move(mangle_context)),
+      llvm_context_(llvm_context),
+      code_generator_(code_generator) {}
 
 CppFile::~CppFile() = default;
 
@@ -45,11 +50,6 @@ auto CppFile::ast_context() const -> const clang::ASTContext& {
   return clang_->getASTContext();
 }
 
-auto CppFile::CreateMangleContext() -> void {
-  CARBON_CHECK(!mangle_context_);
-  mangle_context_.reset(ast_context().createMangleContext());
-}
-
 auto CppFile::mangle_context() const -> clang::MangleContext& {
   return *mangle_context_;
 }
diff --git a/toolchain/sem_ir/cpp_file.h b/toolchain/sem_ir/cpp_file.h
index ecab3f701a2d..a046f1af71fb 100644
--- a/toolchain/sem_ir/cpp_file.h
+++ b/toolchain/sem_ir/cpp_file.h
@@ -29,7 +29,9 @@ namespace Carbon::SemIR {
 class CppFile {
  public:
   explicit CppFile(std::shared_ptr<clang::CompilerInstance> clang,
-                   llvm::LLVMContext* llvm_context);
+                   std::unique_ptr<clang::MangleContext> mangle_context,
+                   llvm::LLVMContext* llvm_context,
+                   clang::CodeGenerator* code_generator);
   ~CppFile();
 
   // Access to compilation options.
@@ -47,28 +49,18 @@ class CppFile {
   auto ast_context() -> clang::ASTContext&;
   auto ast_context() const -> const clang::ASTContext&;
 
-  // Creates the mangle context for this file's C++ AST. Must be called once the
-  // AST context is available (after the frontend begins the source file) and
-  // before `mangle_context()` is used.
-  auto CreateMangleContext() -> void;
   auto mangle_context() const -> clang::MangleContext&;
 
   auto llvm_context() const -> llvm::LLVMContext* { return llvm_context_; }
-  auto SetCodeGenerator(clang::CodeGenerator* code_generator) -> void {
-    code_generator_ = code_generator;
-  }
-  auto GetCodeGenerator() const -> clang::CodeGenerator* {
-    // Clang code generation should not actually modify the AST, but isn't
-    // const-correct.
+  auto code_generator() const -> clang::CodeGenerator* {
     return code_generator_;
   }
 
  private:
   std::shared_ptr<clang::CompilerInstance> clang_;
-  llvm::LLVMContext* llvm_context_;
-  clang::CodeGenerator* code_generator_ = nullptr;
-  // Created by `CreateMangleContext()` once the AST context is available.
   std::unique_ptr<clang::MangleContext> mangle_context_;
+  llvm::LLVMContext* llvm_context_;
+  clang::CodeGenerator* code_generator_;
 };
 
 }  // namespace Carbon::SemIR
diff --git a/toolchain/sem_ir/mangler.cpp b/toolchain/sem_ir/mangler.cpp
index 4dfc3900323a..7f49b410b1a8 100644
--- a/toolchain/sem_ir/mangler.cpp
+++ b/toolchain/sem_ir/mangler.cpp
@@ -271,7 +271,7 @@ auto Mangler::MangleWithPlatform(SemIR::FunctionId function_id,
   // The only platform mangling that's relevant for us is applying a global
   // prefix, if the platform has one.
   if (char prefix = sem_ir_.cpp_file()
-                        ->GetCodeGenerator()
+                        ->code_generator()
                         ->GetModule()
                         ->getDataLayout()
                         .getGlobalPrefix()) {