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Handle signature mismatch when a Carbon function overrides a C++ virtual function. (#7499)

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When a Carbon virtual function overrides a C++ virtual function, we need
to export it with the C++ signature in order for it to work as an
override. Instead of mapping the C++ signature into Carbon and then back
again, use the original C++ signature from the base class as the
signature exported to C++.

Also add documentation explaining how we use thunks in C++ interop,
including in this new virtual function handling logic.
This commit is contained in:
Richard Smith
2026-07-15 18:42:03 +00:00
committed by GitHub
parent 14e8bffe24
commit 9ae73d2847
14 changed files with 635 additions and 174 deletions
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toolchain/lower/testdata/interop/cpp/class/virtual_fn.carbon
Vendored
+7 -8
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@@ -82,8 +82,8 @@ void delete_new_Base() {
// CHECK:STDOUT: $_ZTSN6Carbon4BaseE = comdat any
// CHECK:STDOUT:
// CHECK:STDOUT: @_ZTV1A = available_externally constant { [5 x ptr] } { [5 x ptr] [ptr null, ptr @_ZTI1A, ptr @__cxa_pure_virtual, ptr @__cxa_pure_virtual, ptr @_ZNK1A1FEv] }, align 8
// CHECK:STDOUT: @_ZTVN6Carbon5FinalE = linkonce_odr dso_local constant { [6 x ptr] } { [6 x ptr] [ptr null, ptr @_ZTIN6Carbon5FinalE, ptr @_ZN6Carbon5FinalD2Ev, ptr @_ZN6Carbon5FinalD0Ev, ptr @_ZNK1A1FEv, ptr @_ZN6Carbon5Final1FEv] }, comdat, align 8
// CHECK:STDOUT: @_ZTVN6Carbon4BaseE = linkonce_odr dso_local constant { [6 x ptr] } { [6 x ptr] [ptr null, ptr @_ZTIN6Carbon4BaseE, ptr @_ZN6Carbon4BaseD2Ev, ptr @_ZN6Carbon4BaseD0Ev, ptr @_ZNK1A1FEv, ptr @_ZN6Carbon4Base1FEv] }, comdat, align 8
// CHECK:STDOUT: @_ZTVN6Carbon5FinalE = linkonce_odr dso_local constant { [5 x ptr] } { [5 x ptr] [ptr null, ptr @_ZTIN6Carbon5FinalE, ptr @_ZN6Carbon5FinalD2Ev, ptr @_ZN6Carbon5FinalD0Ev, ptr @_ZNK6Carbon5Final1FEv] }, comdat, align 8
// CHECK:STDOUT: @_ZTVN6Carbon4BaseE = linkonce_odr dso_local constant { [5 x ptr] } { [5 x ptr] [ptr null, ptr @_ZTIN6Carbon4BaseE, ptr @_ZN6Carbon4BaseD2Ev, ptr @_ZN6Carbon4BaseD0Ev, ptr @_ZNK6Carbon4Base1FEv] }, comdat, align 8
// CHECK:STDOUT: @_ZTI1A = external constant ptr
// CHECK:STDOUT: @_ZTIN6Carbon5FinalE = linkonce_odr dso_local constant { ptr, ptr, ptr } { ptr getelementptr inbounds (ptr, ptr @_ZTVN10__cxxabiv120__si_class_type_infoE, i64 2), ptr @_ZTSN6Carbon5FinalE, ptr @_ZTI1A }, comdat, align 8
// CHECK:STDOUT: @_ZTVN10__cxxabiv120__si_class_type_infoE = external global [0 x ptr]
@@ -126,7 +126,7 @@ void delete_new_Base() {
// CHECK:STDOUT: store ptr %this, ptr %this.addr, align 8, !tbaa !12
// CHECK:STDOUT: %this1 = load ptr, ptr %this.addr, align 8
// CHECK:STDOUT: call void @_ZN1AC2Ev(ptr noundef nonnull align 8 dereferenceable(8) %this1) #8
// CHECK:STDOUT: store ptr getelementptr inbounds inrange(-16, 32) ({ [6 x ptr] }, ptr @_ZTVN6Carbon5FinalE, i32 0, i32 0, i32 2), ptr %this1, align 8, !tbaa !15
// CHECK:STDOUT: store ptr getelementptr inbounds inrange(-16, 24) ({ [5 x ptr] }, ptr @_ZTVN6Carbon5FinalE, i32 0, i32 0, i32 2), ptr %this1, align 8, !tbaa !15
// CHECK:STDOUT: ret void
// CHECK:STDOUT: }
// CHECK:STDOUT:
@@ -178,7 +178,7 @@ void delete_new_Base() {
// CHECK:STDOUT: store ptr %this, ptr %this.addr, align 8, !tbaa !17
// CHECK:STDOUT: %this1 = load ptr, ptr %this.addr, align 8
// CHECK:STDOUT: call void @_ZN1AC2Ev(ptr noundef nonnull align 8 dereferenceable(8) %this1) #8
// CHECK:STDOUT: store ptr getelementptr inbounds inrange(-16, 32) ({ [6 x ptr] }, ptr @_ZTVN6Carbon4BaseE, i32 0, i32 0, i32 2), ptr %this1, align 8, !tbaa !15
// CHECK:STDOUT: store ptr getelementptr inbounds inrange(-16, 24) ({ [5 x ptr] }, ptr @_ZTVN6Carbon4BaseE, i32 0, i32 0, i32 2), ptr %this1, align 8, !tbaa !15
// CHECK:STDOUT: ret void
// CHECK:STDOUT: }
// CHECK:STDOUT:
@@ -278,7 +278,7 @@ void delete_new_Base() {
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: alwaysinline mustprogress nounwind uwtable
// CHECK:STDOUT: define internal void @_ZN6Carbon5Final1FEv(ptr noundef nonnull align 8 dereferenceable(8) %this) unnamed_addr #5 align 2 {
// CHECK:STDOUT: define internal void @_ZNK6Carbon5Final1FEv(ptr noundef nonnull align 8 dereferenceable(8) %this) unnamed_addr #5 align 2 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: %this.addr = alloca ptr, align 8
// CHECK:STDOUT: store ptr %this, ptr %this.addr, align 8, !tbaa !12
@@ -293,7 +293,7 @@ void delete_new_Base() {
// 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: store ptr getelementptr inbounds inrange(-16, 32) ({ [6 x ptr] }, ptr @_ZTVN6Carbon4BaseE, i32 0, i32 0, i32 2), ptr %this1, align 8, !tbaa !15
// CHECK:STDOUT: store ptr getelementptr inbounds inrange(-16, 24) ({ [5 x ptr] }, ptr @_ZTVN6Carbon4BaseE, i32 0, i32 0, i32 2), ptr %this1, align 8, !tbaa !15
// CHECK:STDOUT: call void @"_C__destroy_thunk:thunk.Base.Main"(ptr noundef nonnull align 8 dereferenceable(8) %this1)
// CHECK:STDOUT: call void @_ZN1AD2Ev(ptr noundef nonnull align 8 dead_on_return(8) dereferenceable(8) %this1) #8
// CHECK:STDOUT: ret void
@@ -311,7 +311,7 @@ void delete_new_Base() {
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: alwaysinline mustprogress nounwind uwtable
// CHECK:STDOUT: define internal void @_ZN6Carbon4Base1FEv(ptr noundef nonnull align 8 dereferenceable(8) %this) unnamed_addr #5 align 2 {
// CHECK:STDOUT: define internal void @_ZNK6Carbon4Base1FEv(ptr noundef nonnull align 8 dereferenceable(8) %this) unnamed_addr #5 align 2 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: %this.addr = alloca ptr, align 8
// CHECK:STDOUT: store ptr %this, ptr %this.addr, align 8, !tbaa !17
@@ -336,7 +336,6 @@ void delete_new_Base() {
// CHECK:STDOUT: ; uselistorder directives
// CHECK:STDOUT: uselistorder ptr @_ZN6Carbon5FinalD2Ev, { 2, 1, 0 }
// CHECK:STDOUT: uselistorder ptr @__cxa_pure_virtual, { 1, 0 }
// CHECK:STDOUT: uselistorder ptr @_ZNK1A1FEv, { 2, 1, 0 }
// CHECK:STDOUT: uselistorder ptr @_ZN6Carbon4BaseD2Ev, { 1, 0 }
// CHECK:STDOUT: uselistorder ptr @_ZN1AC2Ev, { 1, 0 }
// CHECK:STDOUT: uselistorder ptr @_ZN1AD2Ev, { 1, 0 }