llvm-gcc treats a tentative definition with a previous

(or follow up) extern declaration with weak_import as 
an actual definition. make clang follows this behavior. 
// rdar://9538608
llvm-gcc treats an extern declaration with weak_import

llvm-svn: 133450

2 files changed, 8 insertions, 1 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 57b4f7f..7f4546f 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -1351,7 +1351,8 @@ CodeGenModule::GetLLVMLinkageVarDefinition(const VarDecl *D,
            ((!CodeGenOpts.NoCommon && !D->getAttr<NoCommonAttr>()) ||
              D->getAttr<CommonAttr>()) &&
            !D->hasExternalStorage() && !D->getInit() &&
-           !D->getAttr<SectionAttr>() && !D->isThreadSpecified()) {
+           !D->getAttr<SectionAttr>() && !D->isThreadSpecified() &&
+           !D->getAttr<WeakImportAttr>()) {
     // Thread local vars aren't considered common linkage.
     return llvm::GlobalVariable::CommonLinkage;
   }
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 897b01d..fe3b3b4 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -2039,6 +2039,12 @@ void Sema::MergeVarDecl(VarDecl *New, LookupResult &Previous) {
   }
   
   mergeDeclAttributes(New, Old, Context);
+  // weak_import on current declaration is applied to previous
+  // tentative definiton.
+  if (New->getAttr<WeakImportAttr>() &&
+      Old->getStorageClass() == SC_None &&
+      !Old->getAttr<WeakImportAttr>())
+    Old->addAttr(::new (Context) WeakImportAttr(SourceLocation(), Context));
 
   // Merge the types.
   MergeVarDeclTypes(New, Old);