[clang][bytecode] Fix diagnostic difference with opaque call cmps (#129702)

Try to dig out the call expression and diagnose this as an opaque call.

Author: tbaederr

clang/lib/AST/ByteCode/Interp.h

@@ -1006,6 +1006,14 @@ inline bool CmpHelper<Pointer>(InterpState &S, CodePtr OpPC, CompareFn Fn) {
   }
 }
 
+static inline bool IsOpaqueConstantCall(const CallExpr *E) {
+  unsigned Builtin = E->getBuiltinCallee();
+  return (Builtin == Builtin::BI__builtin___CFStringMakeConstantString ||
+          Builtin == Builtin::BI__builtin___NSStringMakeConstantString ||
+          Builtin == Builtin::BI__builtin_ptrauth_sign_constant ||
+          Builtin == Builtin::BI__builtin_function_start);
+}
+
 template <>
 inline bool CmpHelperEQ<Pointer>(InterpState &S, CodePtr OpPC, CompareFn Fn) {
   using BoolT = PrimConv<PT_Bool>::T;
@@ -1065,11 +1073,19 @@ inline bool CmpHelperEQ<Pointer>(InterpState &S, CodePtr OpPC, CompareFn Fn) {
   for (const auto &P : {LHS, RHS}) {
     if (P.isZero())
       continue;
-    if (BothNonNull && P.pointsToLiteral() &&
-        isa<StringLiteral>(P.getDeclDesc()->asExpr())) {
-      const SourceInfo &Loc = S.Current->getSource(OpPC);
-      S.FFDiag(Loc, diag::note_constexpr_literal_comparison);
-      return false;
+    if (BothNonNull && P.pointsToLiteral()) {
+      const Expr *E = P.getDeclDesc()->asExpr();
+      if (isa<StringLiteral>(E)) {
+        const SourceInfo &Loc = S.Current->getSource(OpPC);
+        S.FFDiag(Loc, diag::note_constexpr_literal_comparison);
+        return false;
+      } else if (const auto *CE = dyn_cast<CallExpr>(E);
+                 CE && IsOpaqueConstantCall(CE)) {
+        const SourceInfo &Loc = S.Current->getSource(OpPC);
+        S.FFDiag(Loc, diag::note_constexpr_opaque_call_comparison)
+            << P.toDiagnosticString(S.getASTContext());
+        return false;
+      }
     }
   }
 

clang/test/AST/ByteCode/builtin-functions.cpp

@@ -1008,9 +1008,8 @@ namespace shufflevector {
 
 namespace FunctionStart {
   void a(void) {}
-  static_assert(__builtin_function_start(a) == a, ""); // ref-error {{not an integral constant expression}} \
-                                                       // ref-note {{comparison against opaque constant address '&__builtin_function_start(a)'}} \
-                                                       // expected-error {{static assertion failed}}
+  static_assert(__builtin_function_start(a) == a, ""); // both-error {{not an integral constant expression}} \
+                                                       // both-note {{comparison against opaque constant address '&__builtin_function_start(a)'}}
 }
 
 namespace BuiltinInImplicitCtor {