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Give thunks weak_odr linkage. (#7525)

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We can end up emitting the same thunk from multiple compilations in some
cases -- in particular, when the thunk is wrapping a function that is
either synthesized by the compiler or imported from C++. When this
happens, we will have multiple-definition link errors unless we allow
redefinitions across multiple files.

It'd be nice to detect when we need to do this and when we don't, but
that's a bit tricky to do in practice. Ideally, in fact, we would use a
different strategy, and emit the thunks as discardable definitions in
each compilation that *uses* them. But for now emitting them with
weak_odr linkage seems like a good way to make progress.
This commit is contained in:
Richard Smith
2026-07-17 13:25:19 +00:00
committed by GitHub
parent 643ab57f5a
commit 5c544f7c2f
20 changed files with 362 additions and 75 deletions
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toolchain/lower/testdata/interop/cpp/class/virtual_fn.carbon
Vendored
+4 -4
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@@ -198,7 +198,7 @@ void delete_new_Base() {
// CHECK:STDOUT: declare void @_CF.Final.Main(ptr)
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: alwaysinline nounwind
// CHECK:STDOUT: define void @"_CF:thunk:A.Cpp:Final.Main"(ptr %self) #6 !dbg !23 {
// CHECK:STDOUT: define weak_odr void @"_CF:thunk:A.Cpp:Final.Main"(ptr %self) #6 !dbg !23 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: call void @_CF.Final.Main(ptr %self), !dbg !29
// CHECK:STDOUT: ret void, !dbg !29
@@ -207,14 +207,14 @@ void delete_new_Base() {
// CHECK:STDOUT: declare void @_CF.Base.Main(ptr)
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: alwaysinline nounwind
// CHECK:STDOUT: define void @"_CF:thunk:A.Cpp:Base.Main"(ptr %self) #6 !dbg !30 {
// CHECK:STDOUT: define weak_odr void @"_CF:thunk:A.Cpp:Base.Main"(ptr %self) #6 !dbg !30 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: call void @_CF.Base.Main(ptr %self), !dbg !33
// CHECK:STDOUT: ret void, !dbg !33
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: alwaysinline nounwind
// CHECK:STDOUT: define void @"_C__destroy_thunk:thunk.Final.Main"(ptr %self) #6 !dbg !34 {
// CHECK:STDOUT: define weak_odr void @"_C__destroy_thunk:thunk.Final.Main"(ptr %self) #6 !dbg !34 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: call void @"_COp.6622c02ec7a967c3:core.Destroy.Core"(ptr %self), !dbg !37
// CHECK:STDOUT: ret void, !dbg !37
@@ -243,7 +243,7 @@ void delete_new_Base() {
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: alwaysinline nounwind
// CHECK:STDOUT: define void @"_C__destroy_thunk:thunk.Base.Main"(ptr %self) #6 !dbg !50 {
// CHECK:STDOUT: define weak_odr void @"_C__destroy_thunk:thunk.Base.Main"(ptr %self) #6 !dbg !50 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: call void @"_COp.a45b619846c20518:core.Destroy.Core"(ptr %self), !dbg !53
// CHECK:STDOUT: ret void, !dbg !53