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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/operators.carbon
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+6 -6
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@@ -146,7 +146,7 @@ fn Driver(x: Cpp.A, y: Cpp.A) {
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: alwaysinline nounwind
// CHECK:STDOUT: define i1 @"_CEqual:thunk:EqWith.ffb401eeee8c4872.Core:Cpp"(ptr %self, ptr %other) #2 !dbg !30 {
// CHECK:STDOUT: define weak_odr i1 @"_CEqual:thunk:EqWith.ffb401eeee8c4872.Core:Cpp"(ptr %self, ptr %other) #2 !dbg !30 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: %.6.temp = alloca i1, align 1, !dbg !36
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %.6.temp), !dbg !36
@@ -156,7 +156,7 @@ fn Driver(x: Cpp.A, y: Cpp.A) {
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: alwaysinline nounwind
// CHECK:STDOUT: define i1 @"_CNotEqual:thunk:EqWith.ffb401eeee8c4872.Core:Cpp"(ptr %self, ptr %other) #2 !dbg !37 {
// CHECK:STDOUT: define weak_odr i1 @"_CNotEqual:thunk:EqWith.ffb401eeee8c4872.Core:Cpp"(ptr %self, ptr %other) #2 !dbg !37 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: %.6.temp = alloca i1, align 1, !dbg !41
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %.6.temp), !dbg !41
@@ -412,7 +412,7 @@ fn Driver(x: Cpp.A, y: Cpp.A) {
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: alwaysinline nounwind
// CHECK:STDOUT: define i1 @"_CLess:thunk:OrderedWith.92c0df05bd55f97a.Core:Cpp"(ptr %self, ptr %other) #2 !dbg !30 {
// CHECK:STDOUT: define weak_odr i1 @"_CLess:thunk:OrderedWith.92c0df05bd55f97a.Core:Cpp"(ptr %self, ptr %other) #2 !dbg !30 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: %.6.temp = alloca i1, align 1, !dbg !36
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %.6.temp), !dbg !36
@@ -422,7 +422,7 @@ fn Driver(x: Cpp.A, y: Cpp.A) {
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: alwaysinline nounwind
// CHECK:STDOUT: define i1 @"_CLessOrEquivalent:thunk:OrderedWith.92c0df05bd55f97a.Core:Cpp"(ptr %self, ptr %other) #2 !dbg !37 {
// CHECK:STDOUT: define weak_odr i1 @"_CLessOrEquivalent:thunk:OrderedWith.92c0df05bd55f97a.Core:Cpp"(ptr %self, ptr %other) #2 !dbg !37 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: %.6.temp = alloca i1, align 1, !dbg !41
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %.6.temp), !dbg !41
@@ -432,7 +432,7 @@ fn Driver(x: Cpp.A, y: Cpp.A) {
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: alwaysinline nounwind
// CHECK:STDOUT: define i1 @"_CGreater:thunk:OrderedWith.92c0df05bd55f97a.Core:Cpp"(ptr %self, ptr %other) #2 !dbg !42 {
// CHECK:STDOUT: define weak_odr i1 @"_CGreater:thunk:OrderedWith.92c0df05bd55f97a.Core:Cpp"(ptr %self, ptr %other) #2 !dbg !42 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: %.6.temp = alloca i1, align 1, !dbg !46
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %.6.temp), !dbg !46
@@ -442,7 +442,7 @@ fn Driver(x: Cpp.A, y: Cpp.A) {
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: alwaysinline nounwind
// CHECK:STDOUT: define i1 @"_CGreaterOrEquivalent:thunk:OrderedWith.92c0df05bd55f97a.Core:Cpp"(ptr %self, ptr %other) #2 !dbg !47 {
// CHECK:STDOUT: define weak_odr i1 @"_CGreaterOrEquivalent:thunk:OrderedWith.92c0df05bd55f97a.Core:Cpp"(ptr %self, ptr %other) #2 !dbg !47 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: %.6.temp = alloca i1, align 1, !dbg !51
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %.6.temp), !dbg !51