The address of a TLS var is not compile-time constant (PR13720)

This makes Clang produce an error for code such as:

  __thread int x;
  int *p = &x;

The lvalue of a thread-local variable cannot be evaluated at compile
time.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@162835 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/AST/ExprConstant.cpp b/lib/AST/ExprConstant.cpp
index e2d5c75..6b88246 100644
--- a/lib/AST/ExprConstant.cpp
+++ b/lib/AST/ExprConstant.cpp
@@ -2832,6 +2832,8 @@
 }
 
 bool LValueExprEvaluator::VisitVarDecl(const Expr *E, const VarDecl *VD) {
+  if (VD->isThreadSpecified())
+    return false;
   if (!VD->getType()->isReferenceType()) {
     if (isa<ParmVarDecl>(VD)) {
       Result.set(VD, Info.CurrentCall->Index);
diff --git a/test/Sema/init.c b/test/Sema/init.c
index 81a665d..ee3e256 100644
--- a/test/Sema/init.c
+++ b/test/Sema/init.c
@@ -157,3 +157,10 @@
 typedef char strty[10];
 struct vortexstruct { strty s; };
 struct vortexstruct vortexvar = { "asdf" };
+
+// PR13720
+__thread int thread_int;
+int *thread_int_ptr = &thread_int; // expected-error{{initializer element is not a compile-time constant}}
+void f() {
+  int *p = &thread_int; // This is perfectly fine, though.
+}