diff --git a/toolchain/check/testdata/interop/cpp/function/variadic.carbon b/toolchain/check/testdata/interop/cpp/function/variadic.carbon
new file mode 100644
index 000000000000..2885ba8da1bf
--- /dev/null
+++ b/toolchain/check/testdata/interop/cpp/function/variadic.carbon
@@ -0,0 +1,177 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// INCLUDE-FILE: toolchain/testing/testdata/min_prelude/int.carbon
+//
+// AUTOUPDATE
+// TIP: To test this file alone, run:
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/interop/cpp/function/variadic.carbon
+// TIP: To dump output, run:
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/interop/cpp/function/variadic.carbon
+
+// --- variadic.h
+
+template<typename ...T>
+auto foo(int, T...) -> void;
+
+// --- call_variadic.carbon
+
+library "[[@TEST_NAME]]";
+
+import Cpp library "variadic.h";
+
+fn Call1() {
+  //@dump-sem-ir-begin
+  Cpp.foo(1);
+  //@dump-sem-ir-end
+}
+
+fn Call2() {
+  //@dump-sem-ir-begin
+  Cpp.foo(1, 2);
+  //@dump-sem-ir-end
+}
+
+fn Call3() {
+  //@dump-sem-ir-begin
+  Cpp.foo(1, 2, 3);
+  //@dump-sem-ir-end
+}
+
+// CHECK:STDOUT: --- call_variadic.carbon
+// CHECK:STDOUT:
+// CHECK:STDOUT: constants {
+// CHECK:STDOUT:   %empty_tuple.type: type = tuple_type () [concrete]
+// CHECK:STDOUT:   %foo.cpp_overload_set.type: type = cpp_overload_set_type @foo.cpp_overload_set [concrete]
+// CHECK:STDOUT:   %foo.cpp_overload_set.value: %foo.cpp_overload_set.type = cpp_overload_set_value @foo.cpp_overload_set [concrete]
+// CHECK:STDOUT:   %int_1.5b8: Core.IntLiteral = int_value 1 [concrete]
+// CHECK:STDOUT:   %int_32: Core.IntLiteral = int_value 32 [concrete]
+// CHECK:STDOUT:   %i32: type = class_type @Int, @Int(%int_32) [concrete]
+// CHECK:STDOUT:   %foo.type.a5abd1.1: type = fn_type @foo.1 [concrete]
+// CHECK:STDOUT:   %foo.23ea43.1: %foo.type.a5abd1.1 = struct_value () [concrete]
+// CHECK:STDOUT:   %ImplicitAs.type.d14: type = facet_type <@ImplicitAs, @ImplicitAs(%i32)> [concrete]
+// CHECK:STDOUT:   %ImplicitAs.Convert.type.1b6: type = fn_type @ImplicitAs.Convert, @ImplicitAs(%i32) [concrete]
+// CHECK:STDOUT:   %To: Core.IntLiteral = symbolic_binding To, 0 [symbolic]
+// CHECK:STDOUT:   %Core.IntLiteral.as.ImplicitAs.impl.Convert.type.f51: type = fn_type @Core.IntLiteral.as.ImplicitAs.impl.Convert, @Core.IntLiteral.as.ImplicitAs.impl(%To) [symbolic]
+// CHECK:STDOUT:   %Core.IntLiteral.as.ImplicitAs.impl.Convert.2a1: %Core.IntLiteral.as.ImplicitAs.impl.Convert.type.f51 = struct_value () [symbolic]
+// CHECK:STDOUT:   %ImplicitAs.impl_witness.bc9: <witness> = impl_witness imports.%ImplicitAs.impl_witness_table.132, @Core.IntLiteral.as.ImplicitAs.impl(%int_32) [concrete]
+// CHECK:STDOUT:   %Core.IntLiteral.as.ImplicitAs.impl.Convert.type.51e: type = fn_type @Core.IntLiteral.as.ImplicitAs.impl.Convert, @Core.IntLiteral.as.ImplicitAs.impl(%int_32) [concrete]
+// CHECK:STDOUT:   %Core.IntLiteral.as.ImplicitAs.impl.Convert.e9b: %Core.IntLiteral.as.ImplicitAs.impl.Convert.type.51e = struct_value () [concrete]
+// CHECK:STDOUT:   %ImplicitAs.facet: %ImplicitAs.type.d14 = facet_value Core.IntLiteral, (%ImplicitAs.impl_witness.bc9) [concrete]
+// CHECK:STDOUT:   %.322: type = fn_type_with_self_type %ImplicitAs.Convert.type.1b6, %ImplicitAs.facet [concrete]
+// CHECK:STDOUT:   %Core.IntLiteral.as.ImplicitAs.impl.Convert.bound.265: <bound method> = bound_method %int_1.5b8, %Core.IntLiteral.as.ImplicitAs.impl.Convert.e9b [concrete]
+// CHECK:STDOUT:   %Core.IntLiteral.as.ImplicitAs.impl.Convert.specific_fn: <specific function> = specific_function %Core.IntLiteral.as.ImplicitAs.impl.Convert.e9b, @Core.IntLiteral.as.ImplicitAs.impl.Convert(%int_32) [concrete]
+// CHECK:STDOUT:   %bound_method.dfc: <bound method> = bound_method %int_1.5b8, %Core.IntLiteral.as.ImplicitAs.impl.Convert.specific_fn [concrete]
+// CHECK:STDOUT:   %int_1.5d2: %i32 = int_value 1 [concrete]
+// CHECK:STDOUT:   %int_2.ecc: Core.IntLiteral = int_value 2 [concrete]
+// CHECK:STDOUT:   %foo.type.a5abd1.2: type = fn_type @foo.2 [concrete]
+// CHECK:STDOUT:   %foo.23ea43.2: %foo.type.a5abd1.2 = struct_value () [concrete]
+// CHECK:STDOUT:   %Core.IntLiteral.as.ImplicitAs.impl.Convert.bound.393: <bound method> = bound_method %int_2.ecc, %Core.IntLiteral.as.ImplicitAs.impl.Convert.e9b [concrete]
+// CHECK:STDOUT:   %bound_method.9f7: <bound method> = bound_method %int_2.ecc, %Core.IntLiteral.as.ImplicitAs.impl.Convert.specific_fn [concrete]
+// CHECK:STDOUT:   %int_2.ef8: %i32 = int_value 2 [concrete]
+// CHECK:STDOUT:   %int_3.1ba: Core.IntLiteral = int_value 3 [concrete]
+// CHECK:STDOUT:   %foo.type.a5abd1.3: type = fn_type @foo.3 [concrete]
+// CHECK:STDOUT:   %foo.23ea43.3: %foo.type.a5abd1.3 = struct_value () [concrete]
+// CHECK:STDOUT:   %Core.IntLiteral.as.ImplicitAs.impl.Convert.bound.87d: <bound method> = bound_method %int_3.1ba, %Core.IntLiteral.as.ImplicitAs.impl.Convert.e9b [concrete]
+// CHECK:STDOUT:   %bound_method.def: <bound method> = bound_method %int_3.1ba, %Core.IntLiteral.as.ImplicitAs.impl.Convert.specific_fn [concrete]
+// CHECK:STDOUT:   %int_3.822: %i32 = int_value 3 [concrete]
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: imports {
+// CHECK:STDOUT:   %Cpp: <namespace> = namespace file.%Cpp.import_cpp, [concrete] {
+// CHECK:STDOUT:     .foo = %foo.cpp_overload_set.value
+// CHECK:STDOUT:     import Cpp//...
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %foo.cpp_overload_set.value: %foo.cpp_overload_set.type = cpp_overload_set_value @foo.cpp_overload_set [concrete = constants.%foo.cpp_overload_set.value]
+// CHECK:STDOUT:   %foo.decl.bd967b.1: %foo.type.a5abd1.1 = fn_decl @foo.1 [concrete = constants.%foo.23ea43.1] {
+// CHECK:STDOUT:     <elided>
+// CHECK:STDOUT:   } {
+// CHECK:STDOUT:     <elided>
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %Core.import_ref.e24: @Core.IntLiteral.as.ImplicitAs.impl.%Core.IntLiteral.as.ImplicitAs.impl.Convert.type (%Core.IntLiteral.as.ImplicitAs.impl.Convert.type.f51) = import_ref Core//prelude/parts/int, loc{{\d+_\d+}}, loaded [symbolic = @Core.IntLiteral.as.ImplicitAs.impl.%Core.IntLiteral.as.ImplicitAs.impl.Convert (constants.%Core.IntLiteral.as.ImplicitAs.impl.Convert.2a1)]
+// CHECK:STDOUT:   %ImplicitAs.impl_witness_table.132 = impl_witness_table (%Core.import_ref.e24), @Core.IntLiteral.as.ImplicitAs.impl [concrete]
+// CHECK:STDOUT:   %foo.decl.bd967b.2: %foo.type.a5abd1.2 = fn_decl @foo.2 [concrete = constants.%foo.23ea43.2] {
+// CHECK:STDOUT:     <elided>
+// CHECK:STDOUT:   } {
+// CHECK:STDOUT:     <elided>
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %foo.decl.bd967b.3: %foo.type.a5abd1.3 = fn_decl @foo.3 [concrete = constants.%foo.23ea43.3] {
+// CHECK:STDOUT:     <elided>
+// CHECK:STDOUT:   } {
+// CHECK:STDOUT:     <elided>
+// CHECK:STDOUT:   }
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @Call1() {
+// CHECK:STDOUT: !entry:
+// CHECK:STDOUT:   %Cpp.ref: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
+// CHECK:STDOUT:   %foo.ref: %foo.cpp_overload_set.type = name_ref foo, imports.%foo.cpp_overload_set.value [concrete = constants.%foo.cpp_overload_set.value]
+// CHECK:STDOUT:   %int_1: Core.IntLiteral = int_value 1 [concrete = constants.%int_1.5b8]
+// CHECK:STDOUT:   %impl.elem0: %.322 = impl_witness_access constants.%ImplicitAs.impl_witness.bc9, element0 [concrete = constants.%Core.IntLiteral.as.ImplicitAs.impl.Convert.e9b]
+// CHECK:STDOUT:   %bound_method.loc8_11.1: <bound method> = bound_method %int_1, %impl.elem0 [concrete = constants.%Core.IntLiteral.as.ImplicitAs.impl.Convert.bound.265]
+// CHECK:STDOUT:   %specific_fn: <specific function> = specific_function %impl.elem0, @Core.IntLiteral.as.ImplicitAs.impl.Convert(constants.%int_32) [concrete = constants.%Core.IntLiteral.as.ImplicitAs.impl.Convert.specific_fn]
+// CHECK:STDOUT:   %bound_method.loc8_11.2: <bound method> = bound_method %int_1, %specific_fn [concrete = constants.%bound_method.dfc]
+// CHECK:STDOUT:   %Core.IntLiteral.as.ImplicitAs.impl.Convert.call: init %i32 = call %bound_method.loc8_11.2(%int_1) [concrete = constants.%int_1.5d2]
+// CHECK:STDOUT:   %.loc8_11.1: %i32 = value_of_initializer %Core.IntLiteral.as.ImplicitAs.impl.Convert.call [concrete = constants.%int_1.5d2]
+// CHECK:STDOUT:   %.loc8_11.2: %i32 = converted %int_1, %.loc8_11.1 [concrete = constants.%int_1.5d2]
+// CHECK:STDOUT:   %foo.call: init %empty_tuple.type = call imports.%foo.decl.bd967b.1(%.loc8_11.2)
+// CHECK:STDOUT:   <elided>
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @Call2() {
+// CHECK:STDOUT: !entry:
+// CHECK:STDOUT:   %Cpp.ref: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
+// CHECK:STDOUT:   %foo.ref: %foo.cpp_overload_set.type = name_ref foo, imports.%foo.cpp_overload_set.value [concrete = constants.%foo.cpp_overload_set.value]
+// CHECK:STDOUT:   %int_1: Core.IntLiteral = int_value 1 [concrete = constants.%int_1.5b8]
+// CHECK:STDOUT:   %int_2: Core.IntLiteral = int_value 2 [concrete = constants.%int_2.ecc]
+// CHECK:STDOUT:   %impl.elem0.loc14_11: %.322 = impl_witness_access constants.%ImplicitAs.impl_witness.bc9, element0 [concrete = constants.%Core.IntLiteral.as.ImplicitAs.impl.Convert.e9b]
+// CHECK:STDOUT:   %bound_method.loc14_11.1: <bound method> = bound_method %int_1, %impl.elem0.loc14_11 [concrete = constants.%Core.IntLiteral.as.ImplicitAs.impl.Convert.bound.265]
+// CHECK:STDOUT:   %specific_fn.loc14_11: <specific function> = specific_function %impl.elem0.loc14_11, @Core.IntLiteral.as.ImplicitAs.impl.Convert(constants.%int_32) [concrete = constants.%Core.IntLiteral.as.ImplicitAs.impl.Convert.specific_fn]
+// CHECK:STDOUT:   %bound_method.loc14_11.2: <bound method> = bound_method %int_1, %specific_fn.loc14_11 [concrete = constants.%bound_method.dfc]
+// CHECK:STDOUT:   %Core.IntLiteral.as.ImplicitAs.impl.Convert.call.loc14_11: init %i32 = call %bound_method.loc14_11.2(%int_1) [concrete = constants.%int_1.5d2]
+// CHECK:STDOUT:   %.loc14_11.1: %i32 = value_of_initializer %Core.IntLiteral.as.ImplicitAs.impl.Convert.call.loc14_11 [concrete = constants.%int_1.5d2]
+// CHECK:STDOUT:   %.loc14_11.2: %i32 = converted %int_1, %.loc14_11.1 [concrete = constants.%int_1.5d2]
+// CHECK:STDOUT:   %impl.elem0.loc14_14: %.322 = impl_witness_access constants.%ImplicitAs.impl_witness.bc9, element0 [concrete = constants.%Core.IntLiteral.as.ImplicitAs.impl.Convert.e9b]
+// CHECK:STDOUT:   %bound_method.loc14_14.1: <bound method> = bound_method %int_2, %impl.elem0.loc14_14 [concrete = constants.%Core.IntLiteral.as.ImplicitAs.impl.Convert.bound.393]
+// CHECK:STDOUT:   %specific_fn.loc14_14: <specific function> = specific_function %impl.elem0.loc14_14, @Core.IntLiteral.as.ImplicitAs.impl.Convert(constants.%int_32) [concrete = constants.%Core.IntLiteral.as.ImplicitAs.impl.Convert.specific_fn]
+// CHECK:STDOUT:   %bound_method.loc14_14.2: <bound method> = bound_method %int_2, %specific_fn.loc14_14 [concrete = constants.%bound_method.9f7]
+// CHECK:STDOUT:   %Core.IntLiteral.as.ImplicitAs.impl.Convert.call.loc14_14: init %i32 = call %bound_method.loc14_14.2(%int_2) [concrete = constants.%int_2.ef8]
+// CHECK:STDOUT:   %.loc14_14.1: %i32 = value_of_initializer %Core.IntLiteral.as.ImplicitAs.impl.Convert.call.loc14_14 [concrete = constants.%int_2.ef8]
+// CHECK:STDOUT:   %.loc14_14.2: %i32 = converted %int_2, %.loc14_14.1 [concrete = constants.%int_2.ef8]
+// CHECK:STDOUT:   %foo.call: init %empty_tuple.type = call imports.%foo.decl.bd967b.2(%.loc14_11.2, %.loc14_14.2)
+// CHECK:STDOUT:   <elided>
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @Call3() {
+// CHECK:STDOUT: !entry:
+// CHECK:STDOUT:   %Cpp.ref: <namespace> = name_ref Cpp, imports.%Cpp [concrete = imports.%Cpp]
+// CHECK:STDOUT:   %foo.ref: %foo.cpp_overload_set.type = name_ref foo, imports.%foo.cpp_overload_set.value [concrete = constants.%foo.cpp_overload_set.value]
+// CHECK:STDOUT:   %int_1: Core.IntLiteral = int_value 1 [concrete = constants.%int_1.5b8]
+// CHECK:STDOUT:   %int_2: Core.IntLiteral = int_value 2 [concrete = constants.%int_2.ecc]
+// CHECK:STDOUT:   %int_3: Core.IntLiteral = int_value 3 [concrete = constants.%int_3.1ba]
+// CHECK:STDOUT:   %impl.elem0.loc20_11: %.322 = impl_witness_access constants.%ImplicitAs.impl_witness.bc9, element0 [concrete = constants.%Core.IntLiteral.as.ImplicitAs.impl.Convert.e9b]
+// CHECK:STDOUT:   %bound_method.loc20_11.1: <bound method> = bound_method %int_1, %impl.elem0.loc20_11 [concrete = constants.%Core.IntLiteral.as.ImplicitAs.impl.Convert.bound.265]
+// CHECK:STDOUT:   %specific_fn.loc20_11: <specific function> = specific_function %impl.elem0.loc20_11, @Core.IntLiteral.as.ImplicitAs.impl.Convert(constants.%int_32) [concrete = constants.%Core.IntLiteral.as.ImplicitAs.impl.Convert.specific_fn]
+// CHECK:STDOUT:   %bound_method.loc20_11.2: <bound method> = bound_method %int_1, %specific_fn.loc20_11 [concrete = constants.%bound_method.dfc]
+// CHECK:STDOUT:   %Core.IntLiteral.as.ImplicitAs.impl.Convert.call.loc20_11: init %i32 = call %bound_method.loc20_11.2(%int_1) [concrete = constants.%int_1.5d2]
+// CHECK:STDOUT:   %.loc20_11.1: %i32 = value_of_initializer %Core.IntLiteral.as.ImplicitAs.impl.Convert.call.loc20_11 [concrete = constants.%int_1.5d2]
+// CHECK:STDOUT:   %.loc20_11.2: %i32 = converted %int_1, %.loc20_11.1 [concrete = constants.%int_1.5d2]
+// CHECK:STDOUT:   %impl.elem0.loc20_14: %.322 = impl_witness_access constants.%ImplicitAs.impl_witness.bc9, element0 [concrete = constants.%Core.IntLiteral.as.ImplicitAs.impl.Convert.e9b]
+// CHECK:STDOUT:   %bound_method.loc20_14.1: <bound method> = bound_method %int_2, %impl.elem0.loc20_14 [concrete = constants.%Core.IntLiteral.as.ImplicitAs.impl.Convert.bound.393]
+// CHECK:STDOUT:   %specific_fn.loc20_14: <specific function> = specific_function %impl.elem0.loc20_14, @Core.IntLiteral.as.ImplicitAs.impl.Convert(constants.%int_32) [concrete = constants.%Core.IntLiteral.as.ImplicitAs.impl.Convert.specific_fn]
+// CHECK:STDOUT:   %bound_method.loc20_14.2: <bound method> = bound_method %int_2, %specific_fn.loc20_14 [concrete = constants.%bound_method.9f7]
+// CHECK:STDOUT:   %Core.IntLiteral.as.ImplicitAs.impl.Convert.call.loc20_14: init %i32 = call %bound_method.loc20_14.2(%int_2) [concrete = constants.%int_2.ef8]
+// CHECK:STDOUT:   %.loc20_14.1: %i32 = value_of_initializer %Core.IntLiteral.as.ImplicitAs.impl.Convert.call.loc20_14 [concrete = constants.%int_2.ef8]
+// CHECK:STDOUT:   %.loc20_14.2: %i32 = converted %int_2, %.loc20_14.1 [concrete = constants.%int_2.ef8]
+// CHECK:STDOUT:   %impl.elem0.loc20_17: %.322 = impl_witness_access constants.%ImplicitAs.impl_witness.bc9, element0 [concrete = constants.%Core.IntLiteral.as.ImplicitAs.impl.Convert.e9b]
+// CHECK:STDOUT:   %bound_method.loc20_17.1: <bound method> = bound_method %int_3, %impl.elem0.loc20_17 [concrete = constants.%Core.IntLiteral.as.ImplicitAs.impl.Convert.bound.87d]
+// CHECK:STDOUT:   %specific_fn.loc20_17: <specific function> = specific_function %impl.elem0.loc20_17, @Core.IntLiteral.as.ImplicitAs.impl.Convert(constants.%int_32) [concrete = constants.%Core.IntLiteral.as.ImplicitAs.impl.Convert.specific_fn]
+// CHECK:STDOUT:   %bound_method.loc20_17.2: <bound method> = bound_method %int_3, %specific_fn.loc20_17 [concrete = constants.%bound_method.def]
+// CHECK:STDOUT:   %Core.IntLiteral.as.ImplicitAs.impl.Convert.call.loc20_17: init %i32 = call %bound_method.loc20_17.2(%int_3) [concrete = constants.%int_3.822]
+// CHECK:STDOUT:   %.loc20_17.1: %i32 = value_of_initializer %Core.IntLiteral.as.ImplicitAs.impl.Convert.call.loc20_17 [concrete = constants.%int_3.822]
+// CHECK:STDOUT:   %.loc20_17.2: %i32 = converted %int_3, %.loc20_17.1 [concrete = constants.%int_3.822]
+// CHECK:STDOUT:   %foo.call: init %empty_tuple.type = call imports.%foo.decl.bd967b.3(%.loc20_11.2, %.loc20_14.2, %.loc20_17.2)
+// CHECK:STDOUT:   <elided>
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
diff --git a/toolchain/lower/testdata/interop/cpp/template.carbon b/toolchain/lower/testdata/interop/cpp/template.carbon
index 6cc1cfee0ac9..f3abb80e4913 100644
--- a/toolchain/lower/testdata/interop/cpp/template.carbon
+++ b/toolchain/lower/testdata/interop/cpp/template.carbon
@@ -30,6 +30,61 @@ fn PassClass(a: Cpp.Class) -> Cpp.Class {
   return Cpp.identity(a);
 }
 
+// --- variadic.carbon
+
+library "[[@TEST_NAME]]";
+
+import Cpp inline '''
+template<typename ...T>
+auto foo(int, T...) -> void;
+''';
+
+fn Call1() {
+  //@dump-sem-ir-begin
+  Cpp.foo(1);
+  //@dump-sem-ir-end
+}
+
+fn Call2() {
+  //@dump-sem-ir-begin
+  Cpp.foo(1, 2);
+  //@dump-sem-ir-end
+}
+
+fn Call3() {
+  //@dump-sem-ir-begin
+  Cpp.foo(1, 2, 3);
+  //@dump-sem-ir-end
+}
+
+// --- variadic_thunk.carbon
+
+library "[[@TEST_NAME]]";
+
+import Cpp inline '''
+class X {};
+template<typename ...T>
+auto foo(X, T...) -> void;
+''';
+
+fn Call1() {
+  //@dump-sem-ir-begin
+  Cpp.foo({} as Cpp.X);
+  //@dump-sem-ir-end
+}
+
+fn Call2() {
+  //@dump-sem-ir-begin
+  Cpp.foo({} as Cpp.X, 2);
+  //@dump-sem-ir-end
+}
+
+fn Call3() {
+  //@dump-sem-ir-begin
+  Cpp.foo({} as Cpp.X, 2, 3);
+  //@dump-sem-ir-end
+}
+
 // CHECK:STDOUT: ; ModuleID = 'call.carbon'
 // CHECK:STDOUT: source_filename = "call.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"
@@ -108,3 +163,185 @@ fn PassClass(a: Cpp.Class) -> Cpp.Class {
 // CHECK:STDOUT: !12 = distinct !DISubprogram(name: "PassClass", linkageName: "_CPassClass.Main", scope: null, file: !6, line: 10, type: !8, spFlags: DISPFlagDefinition, unit: !5)
 // CHECK:STDOUT: !13 = !DILocation(line: 11, column: 10, scope: !12)
 // CHECK:STDOUT: !14 = !DILocation(line: 11, column: 3, scope: !12)
+// CHECK:STDOUT: ; ModuleID = 'variadic.carbon'
+// CHECK:STDOUT: source_filename = "variadic.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: ; Function Attrs: nounwind
+// CHECK:STDOUT: define void @_CCall1.Main() #0 !dbg !7 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   call void @_Z3fooIJEEviDpT_(i32 1), !dbg !10
+// CHECK:STDOUT:   ret void, !dbg !11
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: declare void @_Z3fooIJEEviDpT_(i32)
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nounwind
+// CHECK:STDOUT: define void @_CCall2.Main() #0 !dbg !12 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   call void @_Z3fooIJiEEviDpT_(i32 1, i32 2), !dbg !13
+// CHECK:STDOUT:   ret void, !dbg !14
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: declare void @_Z3fooIJiEEviDpT_(i32, i32)
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nounwind
+// CHECK:STDOUT: define void @_CCall3.Main() #0 !dbg !15 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   call void @_Z3fooIJiiEEviDpT_(i32 1, i32 2, i32 3), !dbg !16
+// CHECK:STDOUT:   ret void, !dbg !17
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: declare void @_Z3fooIJiiEEviDpT_(i32, i32, i32)
+// CHECK:STDOUT:
+// CHECK:STDOUT: attributes #0 = { nounwind }
+// CHECK:STDOUT:
+// CHECK:STDOUT: !llvm.module.flags = !{!0, !1, !2, !3, !4}
+// CHECK:STDOUT: !llvm.dbg.cu = !{!5}
+// CHECK:STDOUT:
+// CHECK:STDOUT: !0 = !{i32 7, !"Dwarf Version", i32 5}
+// CHECK:STDOUT: !1 = !{i32 2, !"Debug Info Version", i32 3}
+// CHECK:STDOUT: !2 = !{i32 1, !"wchar_size", i32 4}
+// CHECK:STDOUT: !3 = !{i32 8, !"PIC Level", i32 0}
+// CHECK:STDOUT: !4 = !{i32 7, !"PIE Level", i32 2}
+// CHECK:STDOUT: !5 = distinct !DICompileUnit(language: DW_LANG_C, file: !6, producer: "carbon", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug)
+// CHECK:STDOUT: !6 = !DIFile(filename: "variadic.carbon", directory: "")
+// CHECK:STDOUT: !7 = distinct !DISubprogram(name: "Call1", linkageName: "_CCall1.Main", scope: null, file: !6, line: 9, type: !8, spFlags: DISPFlagDefinition, unit: !5)
+// CHECK:STDOUT: !8 = !DISubroutineType(types: !9)
+// CHECK:STDOUT: !9 = !{}
+// CHECK:STDOUT: !10 = !DILocation(line: 11, column: 3, scope: !7)
+// CHECK:STDOUT: !11 = !DILocation(line: 9, column: 1, scope: !7)
+// CHECK:STDOUT: !12 = distinct !DISubprogram(name: "Call2", linkageName: "_CCall2.Main", scope: null, file: !6, line: 15, type: !8, spFlags: DISPFlagDefinition, unit: !5)
+// CHECK:STDOUT: !13 = !DILocation(line: 17, column: 3, scope: !12)
+// CHECK:STDOUT: !14 = !DILocation(line: 15, column: 1, scope: !12)
+// CHECK:STDOUT: !15 = distinct !DISubprogram(name: "Call3", linkageName: "_CCall3.Main", scope: null, file: !6, line: 21, type: !8, spFlags: DISPFlagDefinition, unit: !5)
+// CHECK:STDOUT: !16 = !DILocation(line: 23, column: 3, scope: !15)
+// CHECK:STDOUT: !17 = !DILocation(line: 21, column: 1, scope: !15)
+// CHECK:STDOUT: ; ModuleID = 'variadic_thunk.carbon'
+// CHECK:STDOUT: source_filename = "variadic_thunk.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: %class.X = type { i8 }
+// CHECK:STDOUT:
+// CHECK:STDOUT: @X.val.loc12_12.3 = internal constant {} zeroinitializer
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nounwind
+// CHECK:STDOUT: define void @_CCall1.Main() #0 !dbg !7 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %.loc12_12.2.temp = alloca {}, align 8, !dbg !10
+// CHECK:STDOUT:   call void @llvm.lifetime.start.p0(ptr %.loc12_12.2.temp), !dbg !10
+// CHECK:STDOUT:   call void @llvm.memcpy.p0.p0.i64(ptr align 1 %.loc12_12.2.temp, ptr align 1 @X.val.loc12_12.3, i64 0, i1 false), !dbg !10
+// CHECK:STDOUT:   call void @_Z3fooIJEEv1XDpT_.carbon_thunk(ptr %.loc12_12.2.temp), !dbg !11
+// CHECK:STDOUT:   ret void, !dbg !12
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nounwind
+// CHECK:STDOUT: define void @_CCall2.Main() #0 !dbg !13 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %.loc18_12.2.temp = alloca {}, align 8, !dbg !14
+// CHECK:STDOUT:   call void @llvm.lifetime.start.p0(ptr %.loc18_12.2.temp), !dbg !14
+// CHECK:STDOUT:   call void @llvm.memcpy.p0.p0.i64(ptr align 1 %.loc18_12.2.temp, ptr align 1 @X.val.loc12_12.3, i64 0, i1 false), !dbg !14
+// CHECK:STDOUT:   call void @_Z3fooIJiEEv1XDpT_.carbon_thunk(ptr %.loc18_12.2.temp, i32 2), !dbg !15
+// CHECK:STDOUT:   ret void, !dbg !16
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nounwind
+// CHECK:STDOUT: define void @_CCall3.Main() #0 !dbg !17 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %.loc24_12.2.temp = alloca {}, align 8, !dbg !18
+// CHECK:STDOUT:   call void @llvm.lifetime.start.p0(ptr %.loc24_12.2.temp), !dbg !18
+// CHECK:STDOUT:   call void @llvm.memcpy.p0.p0.i64(ptr align 1 %.loc24_12.2.temp, ptr align 1 @X.val.loc12_12.3, i64 0, i1 false), !dbg !18
+// CHECK:STDOUT:   call void @_Z3fooIJiiEEv1XDpT_.carbon_thunk(ptr %.loc24_12.2.temp, i32 2, i32 3), !dbg !19
+// CHECK:STDOUT:   ret void, !dbg !20
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nocallback nofree nosync nounwind willreturn memory(argmem: readwrite)
+// CHECK:STDOUT: declare void @llvm.lifetime.start.p0(ptr captures(none)) #1
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nocallback nofree nounwind willreturn memory(argmem: readwrite)
+// CHECK:STDOUT: declare void @llvm.memcpy.p0.p0.i64(ptr noalias writeonly captures(none), ptr noalias readonly captures(none), i64, i1 immarg) #2
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: alwaysinline mustprogress
+// CHECK:STDOUT: define dso_local void @_Z3fooIJEEv1XDpT_.carbon_thunk(ptr %0) #3 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %.addr = alloca ptr, align 8
+// CHECK:STDOUT:   %agg.tmp = alloca %class.X, align 1
+// CHECK:STDOUT:   store ptr %0, ptr %.addr, align 8
+// CHECK:STDOUT:   %1 = load ptr, ptr %.addr, align 8
+// CHECK:STDOUT:   call void @_Z3fooIJEEv1XDpT_()
+// CHECK:STDOUT:   ret void
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: declare void @_Z3fooIJEEv1XDpT_() #4
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: alwaysinline mustprogress
+// CHECK:STDOUT: define dso_local void @_Z3fooIJiEEv1XDpT_.carbon_thunk(ptr %0, i32 %1) #3 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %.addr = alloca ptr, align 8
+// CHECK:STDOUT:   %.addr1 = alloca i32, align 4
+// CHECK:STDOUT:   %agg.tmp = alloca %class.X, align 1
+// CHECK:STDOUT:   store ptr %0, ptr %.addr, align 8
+// CHECK:STDOUT:   store i32 %1, ptr %.addr1, align 4
+// CHECK:STDOUT:   %2 = load ptr, ptr %.addr, align 8
+// CHECK:STDOUT:   %3 = load i32, ptr %.addr1, align 4
+// CHECK:STDOUT:   call void @_Z3fooIJiEEv1XDpT_(i32 %3)
+// CHECK:STDOUT:   ret void
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: declare void @_Z3fooIJiEEv1XDpT_(i32) #4
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: alwaysinline mustprogress
+// CHECK:STDOUT: define dso_local void @_Z3fooIJiiEEv1XDpT_.carbon_thunk(ptr %0, i32 %1, i32 %2) #3 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %.addr = alloca ptr, align 8
+// CHECK:STDOUT:   %.addr1 = alloca i32, align 4
+// CHECK:STDOUT:   %.addr2 = alloca i32, align 4
+// CHECK:STDOUT:   %agg.tmp = alloca %class.X, align 1
+// CHECK:STDOUT:   store ptr %0, ptr %.addr, align 8
+// CHECK:STDOUT:   store i32 %1, ptr %.addr1, align 4
+// CHECK:STDOUT:   store i32 %2, ptr %.addr2, align 4
+// CHECK:STDOUT:   %3 = load ptr, ptr %.addr, align 8
+// CHECK:STDOUT:   %4 = load i32, ptr %.addr1, align 4
+// CHECK:STDOUT:   %5 = load i32, ptr %.addr2, align 4
+// CHECK:STDOUT:   call void @_Z3fooIJiiEEv1XDpT_(i32 %4, i32 %5)
+// CHECK:STDOUT:   ret void
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: declare void @_Z3fooIJiiEEv1XDpT_(i32, i32) #4
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; uselistorder directives
+// CHECK:STDOUT: uselistorder ptr @llvm.lifetime.start.p0, { 2, 1, 0 }
+// CHECK:STDOUT: uselistorder ptr @llvm.memcpy.p0.p0.i64, { 2, 1, 0 }
+// CHECK:STDOUT:
+// CHECK:STDOUT: attributes #0 = { nounwind }
+// CHECK:STDOUT: attributes #1 = { nocallback nofree nosync nounwind willreturn memory(argmem: readwrite) }
+// CHECK:STDOUT: attributes #2 = { nocallback nofree nounwind willreturn memory(argmem: readwrite) }
+// CHECK:STDOUT: attributes #3 = { alwaysinline mustprogress "min-legal-vector-width"="0" "no-trapping-math"="true" "stack-protector-buffer-size"="0" "target-cpu"="x86-64" "target-features"="+cmov,+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" }
+// CHECK:STDOUT: attributes #4 = { "no-trapping-math"="true" "stack-protector-buffer-size"="0" "target-cpu"="x86-64" "target-features"="+cmov,+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" }
+// CHECK:STDOUT:
+// CHECK:STDOUT: !llvm.module.flags = !{!0, !1, !2, !3, !4}
+// CHECK:STDOUT: !llvm.dbg.cu = !{!5}
+// CHECK:STDOUT:
+// CHECK:STDOUT: !0 = !{i32 7, !"Dwarf Version", i32 5}
+// CHECK:STDOUT: !1 = !{i32 2, !"Debug Info Version", i32 3}
+// CHECK:STDOUT: !2 = !{i32 1, !"wchar_size", i32 4}
+// CHECK:STDOUT: !3 = !{i32 8, !"PIC Level", i32 0}
+// CHECK:STDOUT: !4 = !{i32 7, !"PIE Level", i32 2}
+// CHECK:STDOUT: !5 = distinct !DICompileUnit(language: DW_LANG_C, file: !6, producer: "carbon", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug)
+// CHECK:STDOUT: !6 = !DIFile(filename: "variadic_thunk.carbon", directory: "")
+// CHECK:STDOUT: !7 = distinct !DISubprogram(name: "Call1", linkageName: "_CCall1.Main", scope: null, file: !6, line: 10, type: !8, spFlags: DISPFlagDefinition, unit: !5)
+// CHECK:STDOUT: !8 = !DISubroutineType(types: !9)
+// CHECK:STDOUT: !9 = !{}
+// CHECK:STDOUT: !10 = !DILocation(line: 12, column: 11, scope: !7)
+// CHECK:STDOUT: !11 = !DILocation(line: 12, column: 3, scope: !7)
+// CHECK:STDOUT: !12 = !DILocation(line: 10, column: 1, scope: !7)
+// CHECK:STDOUT: !13 = distinct !DISubprogram(name: "Call2", linkageName: "_CCall2.Main", scope: null, file: !6, line: 16, type: !8, spFlags: DISPFlagDefinition, unit: !5)
+// CHECK:STDOUT: !14 = !DILocation(line: 18, column: 11, scope: !13)
+// CHECK:STDOUT: !15 = !DILocation(line: 18, column: 3, scope: !13)
+// CHECK:STDOUT: !16 = !DILocation(line: 16, column: 1, scope: !13)
+// CHECK:STDOUT: !17 = distinct !DISubprogram(name: "Call3", linkageName: "_CCall3.Main", scope: null, file: !6, line: 22, type: !8, spFlags: DISPFlagDefinition, unit: !5)
+// CHECK:STDOUT: !18 = !DILocation(line: 24, column: 11, scope: !17)
+// CHECK:STDOUT: !19 = !DILocation(line: 24, column: 3, scope: !17)
+// CHECK:STDOUT: !20 = !DILocation(line: 22, column: 1, scope: !17)