[clang][bytecode] Fix integral cast edge case (#161506)

We were converting the `ASInt` to as sign-less `APInt` too early and
losing the sign information.

Author: tbaederr

clang/lib/AST/ByteCode/Compiler.cpp

@@ -540,7 +540,8 @@ bool Compiler<Emitter>::VisitCastExpr(const CastExpr *CE) {
     if (const auto *IL = dyn_cast<IntegerLiteral>(SubExpr)) {
       if (ToT != PT_IntAP && ToT != PT_IntAPS && FromT != PT_IntAP &&
           FromT != PT_IntAPS && !CE->getType()->isEnumeralType())
-        return this->emitConst(IL->getValue(), CE);
+        return this->emitConst(APSInt(IL->getValue(), !isSignedType(*FromT)),
+                               CE);
       if (!this->emitConst(IL->getValue(), SubExpr))
         return false;
     } else {
@@ -4541,7 +4542,14 @@ bool Compiler<Emitter>::emitConst(T Value, const Expr *E) {
 template <class Emitter>
 bool Compiler<Emitter>::emitConst(const APSInt &Value, PrimType Ty,
                                   const Expr *E) {
-  return this->emitConst(static_cast<const APInt &>(Value), Ty, E);
+  if (Ty == PT_IntAPS)
+    return this->emitConstIntAPS(Value, E);
+  if (Ty == PT_IntAP)
+    return this->emitConstIntAP(Value, E);
+
+  if (Value.isSigned())
+    return this->emitConst(Value.getSExtValue(), Ty, E);
+  return this->emitConst(Value.getZExtValue(), Ty, E);
 }
 
 template <class Emitter>

clang/test/AST/ByteCode/literals.cpp

@@ -28,6 +28,8 @@ static_assert(number != 10, ""); // both-error{{failed}} \
 static_assert(__objc_yes, "");
 static_assert(!__objc_no, "");
 
+static_assert((long long)0x00000000FFFF0000 == 4294901760, "");
+
 constexpr bool b = number;
 static_assert(b, "");
 constexpr int one = true;