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Give explicit template instantiations weak ODR linkage. Former

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iterations of this patch gave explicit template instantiation
link-once ODR linkage, which permitted the back end to eliminate
unused symbols. Weak ODR linkage still requires the symbols to be
generated.

llvm-svn: 98441
This commit is contained in:
Douglas Gregor
2010-03-13 18:23:07 +00:00
parent 13327bbe55
commit b14d123774
10 changed files with 47 additions and 37 deletions
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23
clang/lib/CodeGen/CodeGenModule.cpp
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@@ -285,8 +285,7 @@ GetLinkageForFunction(ASTContext &Context, const FunctionDecl *FD,
break;
case TSK_ExplicitInstantiationDefinition:
// FIXME: explicit instantiation definitions should use weak linkage
return CodeGenModule::GVA_StrongExternal;
return CodeGenModule::GVA_ExplicitTemplateInstantiation;
case TSK_ExplicitInstantiationDeclaration:
case TSK_ImplicitInstantiation:
@@ -343,6 +342,12 @@ CodeGenModule::getFunctionLinkage(const FunctionDecl *D) {
// merged with other definitions. c) C++ has the ODR, so we know the
// definition is dependable.
return llvm::Function::LinkOnceODRLinkage;
} else if (Linkage == GVA_ExplicitTemplateInstantiation) {
// An explicit instantiation of a template has weak linkage, since
// explicit instantiations can occur in multiple translation units
// and must all be equivalent. However, we are not allowed to
// throw away these explicit instantiations.
return llvm::Function::WeakODRLinkage;
} else {
assert(Linkage == GVA_StrongExternal);
// Otherwise, we have strong external linkage.
@@ -589,6 +594,7 @@ bool CodeGenModule::MayDeferGeneration(const ValueDecl *Global) {
// static, static inline, always_inline, and extern inline functions can
// always be deferred. Normal inline functions can be deferred in C99/C++.
// Implicit template instantiations can also be deferred in C++.
if (Linkage == GVA_Internal || Linkage == GVA_C99Inline ||
Linkage == GVA_CXXInline || Linkage == GVA_TemplateInstantiation)
return true;
@@ -1043,15 +1049,15 @@ GetLinkageForVariable(ASTContext &Context, const VarDecl *VD) {
switch (TSK) {
case TSK_Undeclared:
case TSK_ExplicitSpecialization:
// FIXME: ExplicitInstantiationDefinition should be weak!
case TSK_ExplicitInstantiationDefinition:
return CodeGenModule::GVA_StrongExternal;
case TSK_ExplicitInstantiationDeclaration:
llvm_unreachable("Variable should not be instantiated");
// Fall through to treat this like any other instantiation.
case TSK_ExplicitInstantiationDefinition:
return CodeGenModule::GVA_ExplicitTemplateInstantiation;
case TSK_ImplicitInstantiation:
return CodeGenModule::GVA_TemplateInstantiation;
}
@@ -1171,7 +1177,10 @@ void CodeGenModule::EmitGlobalVarDefinition(const VarDecl *D) {
GV->setLinkage(llvm::GlobalVariable::WeakODRLinkage);
else
GV->setLinkage(llvm::GlobalVariable::WeakAnyLinkage);
} else if (Linkage == GVA_TemplateInstantiation)
} else if (Linkage == GVA_TemplateInstantiation ||
Linkage == GVA_ExplicitTemplateInstantiation)
// FIXME: It seems like we can provide more specific linkage here
// (LinkOnceODR, WeakODR).
GV->setLinkage(llvm::GlobalVariable::WeakAnyLinkage);
else if (!getLangOptions().CPlusPlus && !CodeGenOpts.NoCommon &&
!D->hasExternalStorage() && !D->getInit() &&