From ab578bf355029bc61cd37bfd99e1d72028db672f Mon Sep 17 00:00:00 2001
From: Fariborz Jahanian <fjahanian@apple.com>
Date: Mon, 20 Jun 2011 17:50:03 +0000
Subject: [PATCH] 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
---
 clang/lib/CodeGen/CodeGenModule.cpp   |  3 ++-
 clang/lib/Sema/SemaDecl.cpp           |  6 ++++++
 clang/test/CodeGen/attr-weak-import.c | 26 ++++++++++++++++++++++++++
 3 files changed, 34 insertions(+), 1 deletion(-)
 create mode 100644 clang/test/CodeGen/attr-weak-import.c

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 57b4f7f2ae4b..7f4546f07965 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 897b01d09319..fe3b3b4f7c17 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);
diff --git a/clang/test/CodeGen/attr-weak-import.c b/clang/test/CodeGen/attr-weak-import.c
new file mode 100644
index 000000000000..f02d09e81509
--- /dev/null
+++ b/clang/test/CodeGen/attr-weak-import.c
@@ -0,0 +1,26 @@
+// RUN: %clang_cc1 -triple x86_64-darwin-apple -emit-llvm -o - %s | FileCheck %s
+// rdar://9538608
+
+extern int A __attribute__((weak_import));
+int A;
+
+extern int B __attribute__((weak_import));
+extern int B;
+
+int C;
+extern int C __attribute__((weak_import));
+
+extern int D __attribute__((weak_import));
+extern int D __attribute__((weak_import));
+int D;
+
+extern int E __attribute__((weak_import));
+int E;
+extern int E __attribute__((weak_import));
+
+// CHECK: @A = global i32
+// CHECK-NOT: @B =
+// CHECK: @C = global i32
+// CHECK: @D = global i32
+// CHECK: @E = global i32
+