[clang][bytecode] Return an lvalue path for dummy pointers (#111862)

Not doing this is wrong in general and we need to reject expressions
where it would matter differently.

clang/lib/AST/ByteCode/Compiler.cpp

@@ -6006,6 +6006,9 @@ bool Compiler<Emitter>::visitDeclRef(const ValueDecl *D, const Expr *E) {
 
       return this->emitGetPtrParam(It->second.Offset, E);
     }
+
+    if (D->getType()->isReferenceType())
+      return false; // FIXME: Do we need to emit InvalidDeclRef?
   }
 
   // In case we need to re-visit a declaration.
@@ -6042,9 +6045,7 @@ bool Compiler<Emitter>::visitDeclRef(const ValueDecl *D, const Expr *E) {
         const auto typeShouldBeVisited = [&](QualType T) -> bool {
           if (T.isConstant(Ctx.getASTContext()))
             return true;
-          if (const auto *RT = T->getAs<ReferenceType>())
-            return RT->getPointeeType().isConstQualified();
-          return false;
+          return T->isReferenceType();
         };
 
         // DecompositionDecls are just proxies for us.
@@ -6060,9 +6061,12 @@ bool Compiler<Emitter>::visitDeclRef(const ValueDecl *D, const Expr *E) {
         // other words, we're evaluating the initializer, just to know if we can
         // evaluate the initializer.
         if (VD->isLocalVarDecl() && typeShouldBeVisited(VD->getType()) &&
-            VD->getInit() && !VD->getInit()->isValueDependent() &&
-            VD->evaluateValue())
-          return revisit(VD);
+            VD->getInit() && !VD->getInit()->isValueDependent()) {
+
+          if (VD->evaluateValue())
+            return revisit(VD);
+          return this->emitInvalidDeclRef(cast<DeclRefExpr>(E), E);
+        }
       }
     } else {
       if (const auto *VD = dyn_cast<VarDecl>(D);

clang/lib/AST/ByteCode/Pointer.cpp

@@ -253,11 +253,6 @@ APValue Pointer::toAPValue(const ASTContext &ASTCtx) const {
     }
   }
 
-  // FIXME(perf): We compute the lvalue path above, but we can't supply it
-  // for dummy pointers (that causes crashes later in CheckConstantExpression).
-  if (isDummy())
-    Path.clear();
-
   // We assemble the LValuePath starting from the innermost pointer to the
   // outermost one. SO in a.b.c, the first element in Path will refer to
   // the field 'c', while later code expects it to refer to 'a'.

clang/test/AST/ByteCode/cxx1z.cpp

@@ -10,3 +10,6 @@ namespace Temp {
   A<int &, addr({}).n> c; // both-error {{reference to subobject of temporary object}}
   A<int *, &addr({}).n> d; // both-error {{pointer to subobject of temporary object}}
 }
+
+char arr[3];
+A<const char*, &arr[1]> d; // both-error {{refers to subobject '&arr[1]'}}