[clang][Interp] Allow taking the address of a non-const global reference

This is not a read, but the GetGlobal op before failed if the reference
we were taking a pointer of was non-const. Use GetGlobalUnchecked
instead.

Author: tbaederr

clang/lib/AST/Interp/Compiler.cpp

@@ -4906,8 +4906,11 @@ bool Compiler<Emitter>::visitDeclRef(const ValueDecl *D, const Expr *E) {
       return this->emitGetLocal(PT_Ptr, Offset, E);
     return this->emitGetPtrLocal(Offset, E);
   } else if (auto GlobalIndex = P.getGlobal(D)) {
-    if (IsReference)
-      return this->emitGetGlobal(classifyPrim(E), *GlobalIndex, E);
+    if (IsReference) {
+      if (!Ctx.getLangOpts().CPlusPlus11)
+        return this->emitGetGlobal(classifyPrim(E), *GlobalIndex, E);
+      return this->emitGetGlobalUnchecked(classifyPrim(E), *GlobalIndex, E);
+    }
 
     return this->emitGetPtrGlobal(*GlobalIndex, E);
   } else if (const auto *PVD = dyn_cast<ParmVarDecl>(D)) {

clang/lib/AST/Interp/Interp.h

@@ -1255,7 +1255,10 @@ bool GetGlobal(InterpState &S, CodePtr OpPC, uint32_t I) {
 /// Same as GetGlobal, but without the checks.
 template <PrimType Name, class T = typename PrimConv<Name>::T>
 bool GetGlobalUnchecked(InterpState &S, CodePtr OpPC, uint32_t I) {
-  auto *B = S.P.getGlobal(I);
+  const Pointer &Ptr = S.P.getPtrGlobal(I);
+  if (!Ptr.isInitialized())
+    return false;
+  const Block *B = S.P.getGlobal(I);
   S.Stk.push<T>(B->deref<T>());
   return true;
 }

clang/test/AST/Interp/references.cpp

@@ -130,3 +130,8 @@ const char (&nonextended_string_ref)[3] = {"hi"};
 static_assert(nonextended_string_ref[0] == 'h', "");
 static_assert(nonextended_string_ref[1] == 'i', "");
 static_assert(nonextended_string_ref[2] == '\0', "");
+
+/// This isa non-constant context. Reading A is not allowed,
+/// but taking its address is.
+int &&A = 12;
+int arr[!&A];