CodeGen: Fix linkage of reference temporaries

Summary:
A reference temporary should inherit the linkage of the variable it
initializes.  Otherwise, we may hit cases where a reference temporary
wouldn't have the same value in all translation units.

Reviewers: rsmith

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D3515

llvm-svn: 207451

1 files changed, 40 insertions, 12 deletions

diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
index 84abda2dea6..c6f8e20a17c 100644
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -7767,8 +7767,10 @@ GVALinkage ASTContext::GetGVALinkageForFunction(const FunctionDecl *FD) const {
     return GVA_StrongODR;
 
   case TSK_ExplicitInstantiationDeclaration:
+    return GVA_AvailableExternally;
+
   case TSK_ImplicitInstantiation:
-    External = GVA_TemplateInstantiation;
+    External = GVA_DiscardableODR;
     break;
   }
 
@@ -7783,7 +7785,7 @@ GVALinkage ASTContext::GetGVALinkageForFunction(const FunctionDecl *FD) const {
       return External;
 
     // C99 inline semantics, where the symbol is not externally visible.
-    return GVA_C99Inline;
+    return GVA_AvailableExternally;
   }
 
   // C++0x [temp.explicit]p9:
@@ -7794,7 +7796,7 @@ GVALinkage ASTContext::GetGVALinkageForFunction(const FunctionDecl *FD) const {
   //   generated in the translation unit. -- end note ]
   if (FD->getTemplateSpecializationKind() 
                                        == TSK_ExplicitInstantiationDeclaration)
-    return GVA_C99Inline;
+    return GVA_AvailableExternally;
 
   // Functions specified with extern and inline in -fms-compatibility mode
   // forcibly get emitted.  While the body of the function cannot be later
@@ -7802,27 +7804,53 @@ GVALinkage ASTContext::GetGVALinkageForFunction(const FunctionDecl *FD) const {
   if (FD->getMostRecentDecl()->isMSExternInline())
     return GVA_StrongODR;
 
-  return GVA_CXXInline;
+  return GVA_DiscardableODR;
 }
 
 GVALinkage ASTContext::GetGVALinkageForVariable(const VarDecl *VD) {
   if (!VD->isExternallyVisible())
     return GVA_Internal;
 
+  if (VD->isStaticLocal()) {
+    GVALinkage StaticLocalLinkage = GVA_DiscardableODR;
+    const DeclContext *LexicalContext = VD->getParentFunctionOrMethod();
+    while (LexicalContext && !isa<FunctionDecl>(LexicalContext))
+      LexicalContext = LexicalContext->getLexicalParent();
+
+    // Let the static local variable inherit it's linkage from the nearest
+    // enclosing function.
+    if (LexicalContext)
+      StaticLocalLinkage =
+          GetGVALinkageForFunction(cast<FunctionDecl>(LexicalContext));
+
+    // GVA_StrongODR function linkage is stronger than what we need,
+    // downgrade to GVA_DiscardableODR.
+    // This allows us to discard the variable if we never end up needing it.
+    return StaticLocalLinkage == GVA_StrongODR ? GVA_DiscardableODR
+                                               : StaticLocalLinkage;
+  }
+
+  // On Darwin, the backing variable for a C++11 thread_local variable always
+  // has internal linkage; all accesses should just be calls to the
+  // Itanium-specified entry point, which has the normal linkage of the
+  // variable.
+  if (VD->getTLSKind() == VarDecl::TLS_Dynamic &&
+      getTargetInfo().getTriple().isMacOSX())
+    return GVA_Internal;
+
   switch (VD->getTemplateSpecializationKind()) {
   case TSK_Undeclared:
   case TSK_ExplicitSpecialization:
     return 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 GVA_StrongODR;
 
+  case TSK_ExplicitInstantiationDeclaration:
+    return GVA_AvailableExternally;
+
   case TSK_ImplicitInstantiation:
-    return GVA_TemplateInstantiation;
+    return GVA_DiscardableODR;
   }
 
   llvm_unreachable("Invalid Linkage!");
@@ -7878,8 +7906,8 @@ bool ASTContext::DeclMustBeEmitted(const Decl *D) {
     // 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)
+    if (Linkage == GVA_Internal || Linkage == GVA_AvailableExternally ||
+        Linkage == GVA_DiscardableODR)
       return false;
     return true;
   }
@@ -7892,7 +7920,7 @@ bool ASTContext::DeclMustBeEmitted(const Decl *D) {
 
   // Variables that can be needed in other TUs are required.
   GVALinkage L = GetGVALinkageForVariable(VD);
-  if (L != GVA_Internal && L != GVA_TemplateInstantiation)
+  if (L != GVA_Internal && L != GVA_DiscardableODR)
     return true;
 
   // Variables that have destruction with side-effects are required.