[clang][bytecode] Always return false for invalid bcp results (#121467)

Author: tbaederr

clang/lib/AST/ByteCode/InterpBuiltin.cpp

@@ -1544,9 +1544,10 @@ static bool interp__builtin_constant_p(InterpState &S, CodePtr OpPC,
     if (Res.isInvalid()) {
       C.cleanup();
       Stk.clear();
+      return returnInt(false);
     }
 
-    if (!Res.isInvalid() && !Res.empty()) {
+    if (!Res.empty()) {
       const APValue &LV = Res.toAPValue();
       if (LV.isLValue()) {
         APValue::LValueBase Base = LV.getLValueBase();

clang/test/AST/ByteCode/builtin-constant-p.cpp

@@ -12,3 +12,9 @@ static_assert(__builtin_constant_p(I + 10.0), "");
 static_assert(__builtin_constant_p(nullptr), "");
 static_assert(__builtin_constant_p(&I), ""); // both-error {{failed due to requirement}}
 static_assert(__builtin_constant_p((void)I), ""); // both-error {{failed due to requirement}}
+
+extern int z;
+constexpr int foo(int &a) {
+  return __builtin_constant_p(a);
+}
+static_assert(!foo(z));