[clang][Interp] Fix non-initializing MemberExprs

We need to create a value for them, do that via visit()

Author: tbaederr

clang/lib/AST/Interp/ByteCodeExprGen.cpp

@@ -1157,8 +1157,13 @@ bool ByteCodeExprGen<Emitter>::VisitMemberExpr(const MemberExpr *E) {
   if (DiscardResult)
     return this->discard(Base);
 
-  if (!this->delegate(Base))
-    return false;
+  if (Initializing) {
+    if (!this->delegate(Base))
+      return false;
+  } else {
+    if (!this->visit(Base))
+      return false;
+  }
 
   // Base above gives us a pointer on the stack.
   // TODO: Implement non-FieldDecl members.

clang/test/AST/Interp/cxx03.cpp

@@ -0,0 +1,12 @@
+// RUN: %clang_cc1 -std=c++03 -verify=expected,both %s -fexperimental-new-constant-interpreter
+// RUN: %clang_cc1 -std=c++03 -verify=ref,both %s
+
+namespace NonInitializingMemberExpr {
+  struct NonLit {
+    NonLit() : value(0) {}
+    int value;
+  };
+  __attribute__((require_constant_initialization)) const int &nl_subobj_ref = NonLit().value; // both-error {{variable does not have a constant initializer}} \
+                                                                                              // both-note {{required by}} \
+                                                                                              // both-note {{subexpression not valid}}
+}