Make global named registers internal variables

[rengolin]

Summary

To avoid emission of the global variable (on both IR and asm/obj), we need to mark it internal (ie. "should not emit").

[• rafael]

LGTM with a nit.

[rengolin]

Committed in r209289

lib/AST/ASTContext.cpp

   return adjustGVALinkageForDLLAttribute(basicGVALinkageForVariable(*this, VD),
                                          VD);
 }
 
 bool ASTContext::DeclMustBeEmitted(const Decl *D) {
   if (const VarDecl *VD = dyn_cast<VarDecl>(D)) {
     if (!VD->isFileVarDecl())
       return false;
+    // Global named register variables (GNU extension) are never emitted.
+    if (VD->getStorageClass() == SC_Register && !VD->isLocalVarDecl())
+      return false;
   } else if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(D)) {
     // We never need to emit an uninstantiated function template.
     if (FD->getTemplatedKind() == FunctionDecl::TK_FunctionTemplate)
       return false;
   } else
     return false;
 
   // If this is a member of a class template, we do not need to emit it.

test/CodeGen/named_reg_global.c

 // RUN: %clang_cc1 -triple x86_64-linux-gnu -S -emit-llvm %s -o - | FileCheck %s
 // RUN: %clang_cc1 -triple aarch64-linux-gnu -S -emit-llvm %s -o - | FileCheck %s
 // RUN: %clang_cc1 -triple arm64-linux-gnu -S -emit-llvm %s -o - | FileCheck %s
 // RUN: %clang_cc1 -triple armv7-linux-gnu -S -emit-llvm %s -o - | FileCheck %s
 
+// CHECK-NOT: @sp = common global
 register unsigned long current_stack_pointer asm("sp");
 
 // CHECK: define{{.*}} i[[bits:[0-9]+]] @get_stack_pointer_addr()
 // CHECK: [[ret:%[0-9]+]] = call i[[bits]] @llvm.read_register.i[[bits]](metadata !0)
 // CHECK: ret i[[bits]] [[ret]]
 unsigned long get_stack_pointer_addr() {
   return current_stack_pointer;
 }