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[clang] Do not emit template parameter objects as COMDATs when they have internal linkage. #125448

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Feb 3, 2025
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[clang] Do not emit template parameter objects as COMDATs when they have internal linkage. #125448

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2 changes: 1 addition & 1 deletion clang/lib/CodeGen/CodeGenModule.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -3765,7 +3765,7 @@ ConstantAddress CodeGenModule::GetAddrOfTemplateParamObject(
auto *GV = new llvm::GlobalVariable(getModule(), Init->getType(),
/*isConstant=*/true, Linkage, Init, Name);
setGVProperties(GV, TPO);
if (supportsCOMDAT())
if (supportsCOMDAT() && Linkage == llvm::GlobalValue::LinkOnceODRLinkage)
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I recall that in some cases WeakODRLinkage is used. Should the condition be something like !isLocalLinkage()?

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Linkage is set to either LinkOnceODRLinkage or InternalLinkage a few lines above this.

GV->setComdat(TheModule.getOrInsertComdat(GV->getName()));
Emitter.finalize(GV);

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10 changes: 10 additions & 0 deletions clang/test/CodeGenCXX/template-param-objects.cpp
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Expand Up @@ -5,6 +5,9 @@ struct S { char buf[32]; };
template<S s> constexpr const char *begin() { return s.buf; }
template<S s> constexpr const char *end() { return s.buf + __builtin_strlen(s.buf); }

namespace { struct T { char buf[32]; }; }
template<T t> constexpr const char* begin_anon() { return t.buf; }

// ITANIUM: [[HELLO:@_ZTAXtl1StlA32_cLc104ELc101ELc108ELc108ELc111ELc32ELc119ELc111ELc114ELc108ELc100EEEE]]
// MSABI: [[HELLO:@"[?][?]__N2US@@3D0GI@@0GF@@0GM@@0GM@@0GP@@0CA@@0HH@@0GP@@0HC@@0GM@@0GE@@0A@@0A@@0A@@0A@@0A@@0A@@0A@@0A@@0A@@0A@@0A@@0A@@0A@@0A@@0A@@0A@@0A@@0A@@0A@@0A@@0A@@@@@"]]
// ITANIUM-SAME: = linkonce_odr constant { <{ [11 x i8], [21 x i8] }> } { <{ [11 x i8], [21 x i8] }> <{ [11 x i8] c"hello world", [21 x i8] zeroinitializer }> }, comdat
Expand All @@ -19,3 +22,10 @@ const char *p = begin<S{"hello world"}>();
// MSABI: @"?q@@3PEBDEB"
// CHECK-SAME: global ptr getelementptr (i8, ptr [[HELLO]], i64 11)
const char *q = end<S{"hello world"}>();


// CHECK: internal constant { <{ [10 x i8], [22 x i8] }> } { <{ [10 x i8], [22 x i8] }> <{ [10 x i8] c"hello anon", [22 x i8] zeroinitializer }> }
// CHECK-NOT: comdat
// ITANIUM: @r
// MSABI: @"?r@@3PEBDEB"
const char *r = begin_anon<T{"hello anon"}>();