extern "C" should preserve the 'extern' qualifier for VarDecls. Fixes 6853728.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@71957 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/CodeGenModule.cpp

@@ -538,8 +538,9 @@ void CodeGenModule::EmitGlobal(GlobalDecl GD) {
     assert(VD->isFileVarDecl() && "Cannot emit local var decl as global.");
 
     // In C++, if this is marked "extern", defer code generation.
-    if (getLangOptions().CPlusPlus && 
-        VD->getStorageClass() == VarDecl::Extern && !VD->getInit())
+    if (getLangOptions().CPlusPlus && !VD->getInit() &&
+        (VD->getStorageClass() == VarDecl::Extern || 
+         VD->isExternC(getContext())))
       return;
 
     // In C, if this isn't a definition, defer code generation.

test/CodeGenCXX/extern-c.cpp

@@ -0,0 +1,13 @@
+// RUN: clang-cc -emit-llvm %s -o %t &&
+namespace foo {
+
+// RUN: not grep "@a = global i32" %t &&
+extern "C" int a;
+
+// RUN: not grep "@_ZN3foo1bE = global i32" %t &&
+extern int b;
+
+// RUN: grep "@_ZN3foo1cE = global i32" %t | count 1
+int c = 5;
+
+}

test/CodeGenCXX/mangle.cpp

@@ -37,7 +37,7 @@ namespace N { namespace N { void f() { } } }
 extern "C" { namespace N { void unmangled_function() { } } }
 
 // RUN: grep unmangled_variable %t | count 1 &&
-extern "C" { namespace N { int unmangled_variable; } }
+extern "C" { namespace N { int unmangled_variable = 10; } }
 
 // RUN: grep _ZN1N1iE %t | count 1 &&
 namespace N { int i; }