Allow interop with classes with virtual base classes. (#6413)

For now, treat such classes as being final, since we can't correctly
derive from them.

This removes the last category of C++ class that we are entirely unable
to interop with, and is a prerequisite for interop with C++ iostreams
(which have a virtual base class).

toolchain/check/cpp/import.cpp

@@ -742,6 +742,13 @@ static auto GetInheritanceKind(clang::CXXRecordDecl* class_def)
     return SemIR::Class::Final;
   }
 
+  if (class_def->getNumVBases()) {
+    // TODO: We treat classes with virtual bases as final for now. We use the
+    // layout of the class including its virtual bases as its Carbon type
+    // layout, so we wouldn't behave correctly if we derived from it.
+    return SemIR::Class::Final;
+  }
+
   if (class_def->isAbstract()) {
     // If the class has any abstract members, it's abstract.
     return SemIR::Class::Abstract;
@@ -804,8 +811,15 @@ static auto ImportClassObjectRepr(Context& context, SemIR::ClassId class_id,
 
   // Import bases.
   for (const auto& base : clang_def->bases()) {
-    CARBON_CHECK(!base.isVirtual(),
-                 "Should not import definition for class with a virtual base");
+    if (base.isVirtual()) {
+      // If the base is virtual, skip it from the layout. We don't know where it
+      // will actually appear within the complete object layout, as a pointer to
+      // this class might point to a derived type that puts the vbase in a
+      // different place.
+      // TODO: Track that the virtual base existed. Support derived-to-vbase
+      // conversions by generating a clang AST fragment.
+      continue;
+    }
 
     auto [base_type_inst_id, base_type_id] =
         ImportTypeAndDependencies(context, import_ir_inst_id, base.getType());
@@ -844,6 +858,10 @@ static auto ImportClassObjectRepr(Context& context, SemIR::ClassId class_id,
       class_info.base_id = SemIR::InstId::None;
     }
 
+    // TODO: If the base class has virtual bases, the size of the type that we
+    // add to the layout here will be the full size of the class (including
+    // virtual bases), whereas the size actually occupied by this base class is
+    // only the nvsize (excluding virtual bases).
     auto base_offset = base.isVirtual()
                            ? clang_layout.getVBaseClassOffset(base_class)
                            : clang_layout.getBaseClassOffset(base_class);
@@ -2447,17 +2465,6 @@ auto ImportClassDefinitionForClangDecl(Context& context, SemIR::LocId loc_id,
     auto* class_def = class_decl->getDefinition();
     CARBON_CHECK(class_def, "Complete type has no definition");
 
-    if (class_def->getNumVBases()) {
-      // TODO: Handle virtual bases. We don't actually know where they go in the
-      // layout. We may also want to use a different size in the layout for
-      // `partial C`, excluding the virtual base. It's also not entirely safe to
-      // just skip over the virtual base, as the type we would construct would
-      // have a misleading size. For now, treat a C++ class with vbases as
-      // incomplete in Carbon.
-      context.TODO(loc_id, "class with virtual bases");
-      return false;
-    }
-
     BuildClassDefinition(context, import_ir_inst_id, class_id, class_inst_id,
                          class_def);
   } else if (auto* enum_decl = dyn_cast<clang::EnumDecl>(clang_decl)) {

toolchain/check/testdata/interop/cpp/class/base.carbon

@@ -298,30 +298,128 @@ library "[[@TEST_NAME]]";
 import Cpp library "virtual_inheritance.h";
 
 fn Convert(p: Cpp.B*) -> Cpp.A* {
-  // CHECK:STDERR: fail_todo_use_virtual_inheritance.carbon:[[@LINE+21]]:3: error: semantics TODO: `class with virtual bases` [SemanticsTodo]
+  // CHECK:STDERR: fail_todo_use_virtual_inheritance.carbon:[[@LINE+7]]:3: error: cannot implicitly convert expression of type `Cpp.B*` to `Cpp.A*` [ConversionFailure]
   // CHECK:STDERR:   return p;
   // CHECK:STDERR:   ^~~~~~~~~
-  // CHECK:STDERR: fail_todo_use_virtual_inheritance.carbon:[[@LINE+18]]:3: note: while completing C++ type `Cpp.B` [InCppTypeCompletion]
+  // CHECK:STDERR: fail_todo_use_virtual_inheritance.carbon:[[@LINE+4]]:3: note: type `Cpp.B*` does not implement interface `Core.ImplicitAs(Cpp.A*)` [MissingImplInMemberAccessNote]
   // CHECK:STDERR:   return p;
   // CHECK:STDERR:   ^~~~~~~~~
   // CHECK:STDERR:
-  // CHECK:STDERR: fail_todo_use_virtual_inheritance.carbon:[[@LINE+14]]:3: error: semantics TODO: `class with virtual bases` [SemanticsTodo]
+  return p;
+}
+
+// --- diamond.h
+
+struct A {
+  int a;
+};
+
+struct B : virtual A {
+  int b;
+};
+
+struct C : virtual A {
+  int c;
+};
+
+struct D : B, C {
+  int d;
+};
+
+// --- fail_todo_use_diamond.carbon
+
+library "[[@TEST_NAME]]";
+
+import Cpp library "diamond.h";
+
+fn ConvertBA(p: Cpp.B*) -> Cpp.A* {
+  // CHECK:STDERR: fail_todo_use_diamond.carbon:[[@LINE+7]]:3: error: cannot implicitly convert expression of type `Cpp.B*` to `Cpp.A*` [ConversionFailure]
   // CHECK:STDERR:   return p;
   // CHECK:STDERR:   ^~~~~~~~~
-  // CHECK:STDERR: fail_todo_use_virtual_inheritance.carbon:[[@LINE+11]]:3: note: while completing C++ type `Cpp.B` [InCppTypeCompletion]
+  // CHECK:STDERR: fail_todo_use_diamond.carbon:[[@LINE+4]]:3: note: type `Cpp.B*` does not implement interface `Core.ImplicitAs(Cpp.A*)` [MissingImplInMemberAccessNote]
   // CHECK:STDERR:   return p;
   // CHECK:STDERR:   ^~~~~~~~~
   // CHECK:STDERR:
-  // CHECK:STDERR: fail_todo_use_virtual_inheritance.carbon:[[@LINE+7]]:3: error: cannot implicitly convert expression of type `Cpp.B*` to `Cpp.A*` [ConversionFailure]
+  return p;
+}
+
+fn ConvertCA(p: Cpp.C*) -> Cpp.A* {
+  // CHECK:STDERR: fail_todo_use_diamond.carbon:[[@LINE+7]]:3: error: cannot implicitly convert expression of type `Cpp.C*` to `Cpp.A*` [ConversionFailure]
   // CHECK:STDERR:   return p;
   // CHECK:STDERR:   ^~~~~~~~~
-  // CHECK:STDERR: fail_todo_use_virtual_inheritance.carbon:[[@LINE+4]]:3: note: type `Cpp.B*` does not implement interface `Core.ImplicitAs(Cpp.A*)` [MissingImplInMemberAccessNote]
+  // CHECK:STDERR: fail_todo_use_diamond.carbon:[[@LINE+4]]:3: note: type `Cpp.C*` does not implement interface `Core.ImplicitAs(Cpp.A*)` [MissingImplInMemberAccessNote]
   // CHECK:STDERR:   return p;
   // CHECK:STDERR:   ^~~~~~~~~
   // CHECK:STDERR:
   return p;
 }
 
+fn ConvertDB(p: Cpp.D*) -> Cpp.B* {
+  // CHECK:STDERR: fail_todo_use_diamond.carbon:[[@LINE+7]]:3: error: cannot implicitly convert expression of type `Cpp.D*` to `Cpp.B*` [ConversionFailure]
+  // CHECK:STDERR:   return p;
+  // CHECK:STDERR:   ^~~~~~~~~
+  // CHECK:STDERR: fail_todo_use_diamond.carbon:[[@LINE+4]]:3: note: type `Cpp.D*` does not implement interface `Core.ImplicitAs(Cpp.B*)` [MissingImplInMemberAccessNote]
+  // CHECK:STDERR:   return p;
+  // CHECK:STDERR:   ^~~~~~~~~
+  // CHECK:STDERR:
+  return p;
+}
+
+fn ConvertDC(p: Cpp.D*) -> Cpp.C* {
+  // CHECK:STDERR: fail_todo_use_diamond.carbon:[[@LINE+7]]:3: error: cannot implicitly convert expression of type `Cpp.D*` to `Cpp.C*` [ConversionFailure]
+  // CHECK:STDERR:   return p;
+  // CHECK:STDERR:   ^~~~~~~~~
+  // CHECK:STDERR: fail_todo_use_diamond.carbon:[[@LINE+4]]:3: note: type `Cpp.D*` does not implement interface `Core.ImplicitAs(Cpp.C*)` [MissingImplInMemberAccessNote]
+  // CHECK:STDERR:   return p;
+  // CHECK:STDERR:   ^~~~~~~~~
+  // CHECK:STDERR:
+  return p;
+}
+
+fn AccessBA(d: Cpp.D) -> i32 {
+  // CHECK:STDERR: fail_todo_use_diamond.carbon:[[@LINE+7]]:11: error: cannot convert expression of type `Cpp.D` to `Cpp.B` with `as` [ConversionFailure]
+  // CHECK:STDERR:   return (d as Cpp.B).b;
+  // CHECK:STDERR:           ^~~~~~~~~~
+  // CHECK:STDERR: fail_todo_use_diamond.carbon:[[@LINE+4]]:11: note: type `Cpp.D` does not implement interface `Core.As(Cpp.B)` [MissingImplInMemberAccessNote]
+  // CHECK:STDERR:   return (d as Cpp.B).b;
+  // CHECK:STDERR:           ^~~~~~~~~~
+  // CHECK:STDERR:
+  return (d as Cpp.B).b;
+}
+
+fn AccessCA(d: Cpp.D) -> i32 {
+  // CHECK:STDERR: fail_todo_use_diamond.carbon:[[@LINE+7]]:11: error: cannot convert expression of type `Cpp.D` to `Cpp.C` with `as` [ConversionFailure]
+  // CHECK:STDERR:   return (d as Cpp.C).b;
+  // CHECK:STDERR:           ^~~~~~~~~~
+  // CHECK:STDERR: fail_todo_use_diamond.carbon:[[@LINE+4]]:11: note: type `Cpp.D` does not implement interface `Core.As(Cpp.C)` [MissingImplInMemberAccessNote]
+  // CHECK:STDERR:   return (d as Cpp.C).b;
+  // CHECK:STDERR:           ^~~~~~~~~~
+  // CHECK:STDERR:
+  return (d as Cpp.C).b;
+}
+
+fn AccessDB(d: Cpp.D) -> i32 {
+  // CHECK:STDERR: fail_todo_use_diamond.carbon:[[@LINE+7]]:10: error: cannot implicitly convert expression of type `Cpp.D` to `Cpp.B` [ConversionFailure]
+  // CHECK:STDERR:   return d.b;
+  // CHECK:STDERR:          ^~~
+  // CHECK:STDERR: fail_todo_use_diamond.carbon:[[@LINE+4]]:10: note: type `Cpp.D` does not implement interface `Core.ImplicitAs(Cpp.B)` [MissingImplInMemberAccessNote]
+  // CHECK:STDERR:   return d.b;
+  // CHECK:STDERR:          ^~~
+  // CHECK:STDERR:
+  return d.b;
+}
+
+fn AccessDC(d: Cpp.D) -> i32 {
+  // CHECK:STDERR: fail_todo_use_diamond.carbon:[[@LINE+7]]:10: error: cannot implicitly convert expression of type `Cpp.D` to `Cpp.C` [ConversionFailure]
+  // CHECK:STDERR:   return d.c;
+  // CHECK:STDERR:          ^~~
+  // CHECK:STDERR: fail_todo_use_diamond.carbon:[[@LINE+4]]:10: note: type `Cpp.D` does not implement interface `Core.ImplicitAs(Cpp.C)` [MissingImplInMemberAccessNote]
+  // CHECK:STDERR:   return d.c;
+  // CHECK:STDERR:          ^~~
+  // CHECK:STDERR:
+  return d.c;
+}
+
 // --- final.h
 
 struct A final {};

toolchain/check/testdata/interop/cpp/function/operators.carbon

@@ -877,54 +877,6 @@ fn F() {
   let result: i32 = *CreateIncomplete() + complete;
 }
 
-// ============================================================================
-// Unsupported operand type in instantiation
-// ============================================================================
-
-// --- unsupported_in_instantiation.h
-
-struct Supported {};
-
-template<typename T>
-struct Unsupported : public virtual Supported {};
-using UnsupportedAlias = Unsupported<int>;
-extern UnsupportedAlias unsupported;
-
-// --- fail_import_unsupported_in_instantiation_unary.carbon
-
-library "[[@TEST_NAME]]";
-
-import Cpp library "unsupported_in_instantiation.h";
-
-fn F() {
-  // CHECK:STDERR: fail_import_unsupported_in_instantiation_unary.carbon:[[@LINE+7]]:21: error: semantics TODO: `class with virtual bases` [SemanticsTodo]
-  // CHECK:STDERR:   let result: i32 = -Cpp.unsupported;
-  // CHECK:STDERR:                     ^~~~~~~~~~~~~~~~
-  // CHECK:STDERR: fail_import_unsupported_in_instantiation_unary.carbon:[[@LINE+4]]:21: note: while completing C++ type `Cpp.Unsupported` [InCppTypeCompletion]
-  // CHECK:STDERR:   let result: i32 = -Cpp.unsupported;
-  // CHECK:STDERR:                     ^~~~~~~~~~~~~~~~
-  // CHECK:STDERR:
-  let result: i32 = -Cpp.unsupported;
-}
-
-// --- fail_import_unsupported_in_instantiation_binary.carbon
-
-library "[[@TEST_NAME]]";
-
-import Cpp library "unsupported_in_instantiation.h";
-
-fn F() {
-  var supported: Cpp.Supported = Cpp.Supported.Supported();
-  // CHECK:STDERR: fail_import_unsupported_in_instantiation_binary.carbon:[[@LINE+7]]:21: error: semantics TODO: `class with virtual bases` [SemanticsTodo]
-  // CHECK:STDERR:   let result: i32 = supported + Cpp.unsupported;
-  // CHECK:STDERR:                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~
-  // CHECK:STDERR: fail_import_unsupported_in_instantiation_binary.carbon:[[@LINE+4]]:21: note: while completing C++ type `Cpp.Unsupported` [InCppTypeCompletion]
-  // CHECK:STDERR:   let result: i32 = supported + Cpp.unsupported;
-  // CHECK:STDERR:                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~
-  // CHECK:STDERR:
-  let result: i32 = supported + Cpp.unsupported;
-}
-
 // ============================================================================
 // Indirect template instantiation
 // ============================================================================

toolchain/lower/testdata/interop/cpp/virtual_base.carbon

@@ -0,0 +1,197 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// INCLUDE-FILE: toolchain/testing/testdata/min_prelude/int.carbon
+//
+// AUTOUPDATE
+// TIP: To test this file alone, run:
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/lower/testdata/interop/cpp/virtual_base.carbon
+// TIP: To dump output, run:
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/interop/cpp/virtual_base.carbon
+
+// --- diamond.h
+
+struct A {
+  A();
+  int a;
+};
+
+struct B : virtual A {
+  B();
+  int b;
+};
+
+struct C : virtual A {
+  C();
+  int c;
+};
+
+struct D : B, C {
+  int d;
+};
+
+// Layout of D (x86_64):
+//
+// 0:  B | 0: vptr
+// 8:    | 8: int B::b
+// 12: (4 bytes padding)
+// 16: C | 0: vptr
+// 24:   | 8: int C::c
+// 28: int D::d
+// 32: A | 0: int A::a
+// 36: (4 bytes padding)
+// 40: (end of D)
+
+// --- use_diamond.carbon
+
+library "[[@TEST_NAME]]";
+
+import Cpp library "diamond.h";
+
+fn Make() {
+  // This should construct a 40-byte object, using a construtor with a `...C1`
+  // mangled name for D (a complete object constructor), which should call
+  // constructors with `...C2` mangled names for A, B, and C (base subobject
+  // constructors).
+  var d: Cpp.D = Cpp.D.D();
+}
+
+fn AccessD(d: Cpp.D) -> i32 {
+  // This should read an i32 at offset 28.
+  return d.d;
+}
+
+// CHECK:STDOUT: ; ModuleID = 'use_diamond.carbon'
+// CHECK:STDOUT: source_filename = "use_diamond.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: $_ZN1DC1Ev = comdat any
+// CHECK:STDOUT:
+// CHECK:STDOUT: $_ZTV1D = comdat any
+// CHECK:STDOUT:
+// CHECK:STDOUT: $_ZTT1D = comdat any
+// CHECK:STDOUT:
+// CHECK:STDOUT: $_ZTC1D0_1B = comdat any
+// CHECK:STDOUT:
+// CHECK:STDOUT: $_ZTI1B = comdat any
+// CHECK:STDOUT:
+// CHECK:STDOUT: $_ZTS1B = comdat any
+// CHECK:STDOUT:
+// CHECK:STDOUT: $_ZTI1A = comdat any
+// CHECK:STDOUT:
+// CHECK:STDOUT: $_ZTS1A = comdat any
+// CHECK:STDOUT:
+// CHECK:STDOUT: $_ZTC1D16_1C = comdat any
+// CHECK:STDOUT:
+// CHECK:STDOUT: $_ZTI1C = comdat any
+// CHECK:STDOUT:
+// CHECK:STDOUT: $_ZTS1C = comdat any
+// CHECK:STDOUT:
+// CHECK:STDOUT: $_ZTI1D = comdat any
+// CHECK:STDOUT:
+// CHECK:STDOUT: $_ZTS1D = comdat any
+// CHECK:STDOUT:
+// CHECK:STDOUT: @_ZTV1D = linkonce_odr dso_local unnamed_addr constant { [3 x ptr], [3 x ptr] } { [3 x ptr] [ptr inttoptr (i64 32 to ptr), ptr null, ptr @_ZTI1D], [3 x ptr] [ptr inttoptr (i64 16 to ptr), ptr inttoptr (i64 -16 to ptr), ptr @_ZTI1D] }, comdat, align 8
+// CHECK:STDOUT: @_ZTT1D = linkonce_odr dso_local unnamed_addr constant [4 x ptr] [ptr getelementptr inbounds inrange(-24, 0) ({ [3 x ptr], [3 x ptr] }, ptr @_ZTV1D, i32 0, i32 0, i32 3), ptr getelementptr inbounds inrange(-24, 0) ({ [3 x ptr] }, ptr @_ZTC1D0_1B, i32 0, i32 0, i32 3), ptr getelementptr inbounds inrange(-24, 0) ({ [3 x ptr] }, ptr @_ZTC1D16_1C, i32 0, i32 0, i32 3), ptr getelementptr inbounds inrange(-24, 0) ({ [3 x ptr], [3 x ptr] }, ptr @_ZTV1D, i32 0, i32 1, i32 3)], comdat, align 8
+// CHECK:STDOUT: @_ZTC1D0_1B = linkonce_odr dso_local unnamed_addr constant { [3 x ptr] } { [3 x ptr] [ptr inttoptr (i64 32 to ptr), ptr null, ptr @_ZTI1B] }, comdat, align 8
+// CHECK:STDOUT: @_ZTI1B = linkonce_odr dso_local constant { ptr, ptr, i32, i32, ptr, i64 } { ptr getelementptr inbounds (ptr, ptr @_ZTVN10__cxxabiv121__vmi_class_type_infoE, i64 2), ptr @_ZTS1B, i32 0, i32 1, ptr @_ZTI1A, i64 -6141 }, comdat, align 8
+// CHECK:STDOUT: @_ZTVN10__cxxabiv121__vmi_class_type_infoE = external global [0 x ptr]
+// CHECK:STDOUT: @_ZTS1B = linkonce_odr dso_local constant [3 x i8] c"1B\00", comdat, align 1
+// CHECK:STDOUT: @_ZTI1A = linkonce_odr dso_local constant { ptr, ptr } { ptr getelementptr inbounds (ptr, ptr @_ZTVN10__cxxabiv117__class_type_infoE, i64 2), ptr @_ZTS1A }, comdat, align 8
+// CHECK:STDOUT: @_ZTVN10__cxxabiv117__class_type_infoE = external global [0 x ptr]
+// CHECK:STDOUT: @_ZTS1A = linkonce_odr dso_local constant [3 x i8] c"1A\00", comdat, align 1
+// CHECK:STDOUT: @_ZTC1D16_1C = linkonce_odr dso_local unnamed_addr constant { [3 x ptr] } { [3 x ptr] [ptr inttoptr (i64 16 to ptr), ptr null, ptr @_ZTI1C] }, comdat, align 8
+// CHECK:STDOUT: @_ZTI1C = linkonce_odr dso_local constant { ptr, ptr, i32, i32, ptr, i64 } { ptr getelementptr inbounds (ptr, ptr @_ZTVN10__cxxabiv121__vmi_class_type_infoE, i64 2), ptr @_ZTS1C, i32 0, i32 1, ptr @_ZTI1A, i64 -6141 }, comdat, align 8
+// CHECK:STDOUT: @_ZTS1C = linkonce_odr dso_local constant [3 x i8] c"1C\00", comdat, align 1
+// CHECK:STDOUT: @_ZTI1D = linkonce_odr dso_local constant { ptr, ptr, i32, i32, ptr, i64, ptr, i64 } { ptr getelementptr inbounds (ptr, ptr @_ZTVN10__cxxabiv121__vmi_class_type_infoE, i64 2), ptr @_ZTS1D, i32 2, i32 2, ptr @_ZTI1B, i64 2, ptr @_ZTI1C, i64 4098 }, comdat, align 8
+// CHECK:STDOUT: @_ZTS1D = linkonce_odr dso_local constant [3 x i8] c"1D\00", comdat, align 1
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nounwind
+// CHECK:STDOUT: define void @_CMake.Main() #0 !dbg !7 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %d.var = alloca [40 x i8], align 1, !dbg !10
+// CHECK:STDOUT:   call void @llvm.lifetime.start.p0(ptr %d.var), !dbg !10
+// CHECK:STDOUT:   call void @_ZN1DC1Ev.carbon_thunk(ptr %d.var), !dbg !11
+// CHECK:STDOUT:   ret void, !dbg !12
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: nounwind
+// CHECK:STDOUT: define i32 @_CAccessD.Main(ptr %d) #0 !dbg !13 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %.loc16_11.1.d = getelementptr inbounds nuw [40 x i8], ptr %d, i32 0, i32 28, !dbg !14
+// CHECK:STDOUT:   %.loc16_11.2 = load i32, ptr %.loc16_11.1.d, align 4, !dbg !14
+// CHECK:STDOUT:   ret i32 %.loc16_11.2, !dbg !15
+// 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: alwaysinline mustprogress
+// CHECK:STDOUT: define dso_local void @_ZN1DC1Ev.carbon_thunk(ptr %return) #2 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %return.addr = alloca ptr, align 8
+// CHECK:STDOUT:   store ptr %return, ptr %return.addr, align 8
+// CHECK:STDOUT:   %0 = load ptr, ptr %return.addr, align 8
+// CHECK:STDOUT:   call void @_ZN1DC1Ev(ptr nonnull align 8 dereferenceable(32) %0)
+// CHECK:STDOUT:   ret void
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; Function Attrs: mustprogress noinline optnone
+// CHECK:STDOUT: define linkonce_odr dso_local void @_ZN1DC1Ev(ptr nonnull align 8 dereferenceable(32) %this) unnamed_addr #3 comdat align 2 {
+// CHECK:STDOUT: entry:
+// CHECK:STDOUT:   %this.addr = alloca ptr, align 8
+// CHECK:STDOUT:   store ptr %this, ptr %this.addr, align 8
+// CHECK:STDOUT:   %this1 = load ptr, ptr %this.addr, align 8
+// CHECK:STDOUT:   %0 = getelementptr inbounds i8, ptr %this1, i64 32
+// CHECK:STDOUT:   call void @_ZN1AC2Ev(ptr nonnull align 4 dereferenceable(4) %0)
+// CHECK:STDOUT:   call void @_ZN1BC2Ev(ptr nonnull align 8 dereferenceable(12) %this1, ptr getelementptr inbounds ([4 x ptr], ptr @_ZTT1D, i64 0, i64 1))
+// CHECK:STDOUT:   %1 = getelementptr inbounds i8, ptr %this1, i64 16
+// CHECK:STDOUT:   call void @_ZN1CC2Ev(ptr nonnull align 8 dereferenceable(12) %1, ptr getelementptr inbounds ([4 x ptr], ptr @_ZTT1D, i64 0, i64 2))
+// CHECK:STDOUT:   store ptr getelementptr inbounds inrange(-24, 0) ({ [3 x ptr], [3 x ptr] }, ptr @_ZTV1D, i32 0, i32 0, i32 3), ptr %this1, align 8
+// CHECK:STDOUT:   %add.ptr = getelementptr inbounds i8, ptr %this1, i64 16
+// CHECK:STDOUT:   store ptr getelementptr inbounds inrange(-24, 0) ({ [3 x ptr], [3 x ptr] }, ptr @_ZTV1D, i32 0, i32 1, i32 3), ptr %add.ptr, align 8
+// CHECK:STDOUT:   ret void
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: declare void @_ZN1AC2Ev(ptr nonnull align 4 dereferenceable(4)) unnamed_addr #4
+// CHECK:STDOUT:
+// CHECK:STDOUT: declare void @_ZN1BC2Ev(ptr nonnull align 8 dereferenceable(12), ptr) unnamed_addr #4
+// CHECK:STDOUT:
+// CHECK:STDOUT: declare void @_ZN1CC2Ev(ptr nonnull align 8 dereferenceable(12), ptr) unnamed_addr #4
+// CHECK:STDOUT:
+// CHECK:STDOUT: ; uselistorder directives
+// CHECK:STDOUT: uselistorder ptr getelementptr inbounds inrange(-24, 0) ({ [3 x ptr], [3 x ptr] }, ptr @_ZTV1D, i32 0, i32 0, i32 3), { 1, 0 }
+// CHECK:STDOUT: uselistorder ptr getelementptr inbounds inrange(-24, 0) ({ [3 x ptr], [3 x ptr] }, ptr @_ZTV1D, i32 0, i32 1, i32 3), { 1, 0 }
+// CHECK:STDOUT: uselistorder ptr getelementptr inbounds (ptr, ptr @_ZTVN10__cxxabiv121__vmi_class_type_infoE, i64 2), { 2, 1, 0 }
+// CHECK:STDOUT: uselistorder ptr @_ZTI1B, { 1, 0 }
+// CHECK:STDOUT: uselistorder ptr @_ZTI1A, { 1, 0 }
+// CHECK:STDOUT: uselistorder ptr @_ZTI1C, { 1, 0 }
+// CHECK:STDOUT: uselistorder ptr @_ZTI1D, { 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 = { 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 #3 = { mustprogress noinline optnone "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_plus_plus, file: !6, producer: "carbon", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug)
+// CHECK:STDOUT: !6 = !DIFile(filename: "use_diamond.carbon", directory: "")
+// CHECK:STDOUT: !7 = distinct !DISubprogram(name: "Make", linkageName: "_CMake.Main", scope: null, file: !6, line: 6, 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: 11, column: 18, scope: !7)
+// CHECK:STDOUT: !12 = !DILocation(line: 6, column: 1, scope: !7)
+// CHECK:STDOUT: !13 = distinct !DISubprogram(name: "AccessD", linkageName: "_CAccessD.Main", scope: null, file: !6, line: 14, type: !8, spFlags: DISPFlagDefinition, unit: !5)
+// CHECK:STDOUT: !14 = !DILocation(line: 16, column: 10, scope: !13)
+// CHECK:STDOUT: !15 = !DILocation(line: 16, column: 3, scope: !13)