[clang][Interp] Reject reinterpret_casts

[tbaeder]

Summary

An appropriate diagnostic has already been emitted when we get to the expression, so just return false here.

[aaron.ballman]

This is lacking test coverage. (Other interesting related test coverage are casts that perform a reinterpret_cast under the hood but that might be somewhat separate.)

[shafik]

In D137558#3915350, @aaron.ballman wrote:

This is lacking test coverage. (Other interesting related test coverage are casts that perform a reinterpret_cast under the hood but that might be somewhat separate.)

Well I think at least things like C-style casts that basically end up being reinterpret_cast should be tested as well e.g.:

constexpr int x = 1;
constexpr float *fp = (float*)x;

clang/lib/AST/Interp/ByteCodeExprGen.h

 public:
   /// Initializes the compiler and the backend emitter.
   template <typename... Tys>
   ByteCodeExprGen(Context &Ctx, Program &P, Tys &&... Args)
       : Emitter(Ctx, P, Args...), Ctx(Ctx), P(P) {}
 
   // Expression visitors - result returned on interp stack.
   bool VisitCastExpr(const CastExpr *E);
+  bool VisitCXXReinterpretCastExpr(const CXXReinterpretCastExpr *E);
   bool VisitIntegerLiteral(const IntegerLiteral *E);
   bool VisitFloatingLiteral(const FloatingLiteral *E);
   bool VisitParenExpr(const ParenExpr *E);
   bool VisitBinaryOperator(const BinaryOperator *E);
   bool VisitPointerArithBinOp(const BinaryOperator *E);
   bool VisitCXXDefaultArgExpr(const CXXDefaultArgExpr *E);
   bool VisitCallExpr(const CallExpr *E);
   bool VisitCXXMemberCallExpr(const CXXMemberCallExpr *E);

clang/lib/AST/Interp/ByteCodeExprGen.cpp

case CK_ToVoid:
     return discard(SubExpr);
 
   default:
     assert(false && "Cast not implemented");
   }
   llvm_unreachable("Unhandled clang::CastKind enum");
 }
 
+
+template <class Emitter>
+bool ByteCodeExprGen<Emitter>::VisitCXXReinterpretCastExpr(const CXXReinterpretCastExpr *E) {
+  return false;
+}
+
 template <class Emitter>
 bool ByteCodeExprGen<Emitter>::VisitIntegerLiteral(const IntegerLiteral *LE) {
   if (DiscardResult)
     return true;
 
   return this->emitConst(LE->getValue(), LE);
 }