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.

llvm-svn: 162835

clang/lib/AST/ExprConstant.cpp

@@ -2832,6 +2832,8 @@ bool LValueExprEvaluator::VisitDeclRefExpr(const DeclRefExpr *E) {
 }
 
 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);

clang/test/Sema/init.c

@@ -157,3 +157,10 @@ int PR4386_zed() __attribute((weak));
 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.
+}