[clang][Interp] Implement BitXor opcode

[shafik]

Besides the minor comment LGTM

clang/test/AST/Interp/literals.cpp

290

Should also work w/ unscoped enums as well.

clang/lib/AST/Interp/ByteCodeExprGen.cpp

if (Optional<PrimType> T = classify(BO->getType())) {
     case BO_And:
       return Discard(this->emitBitAnd(*T, BO));
     case BO_Or:
       return Discard(this->emitBitOr(*T, BO));
     case BO_Shl:
       return Discard(this->emitShl(*LT, *RT, BO));
     case BO_Shr:
       return Discard(this->emitShr(*LT, *RT, BO));
+    case BO_Xor:
+      return Discard(this->emitBitXor(*T, BO));
     case BO_LAnd:
     case BO_LOr:
     default:
       return this->bail(BO);
     }
   }
 
   return this->bail(BO);

clang/lib/AST/Interp/Integral.h

static bool bitAnd(Integral A, Integral B, unsigned OpBits, Integral *R) {
     return false;
   }
 
   static bool bitOr(Integral A, Integral B, unsigned OpBits, Integral *R) {
     *R = Integral(A.V | B.V);
     return false;
   }
 
+  static bool bitXor(Integral A, Integral B, unsigned OpBits, Integral *R) {
+    *R = Integral(A.V ^ B.V);
+    return false;
+  }
+
   static bool neg(Integral A, Integral *R) {
     *R = -A;
     return false;
   }
 
   static bool comp(Integral A, Integral *R) {
     *R = Integral(~A.V);
     return false;

clang/lib/AST/Interp/Interp.h

if (!T::bitOr(LHS, RHS, Bits, &Result)) {
     S.Stk.push<T>(Result);
     return true;
   }
   return false;
 }
 
 /// 1) Pops the RHS from the stack.
 /// 2) Pops the LHS from the stack.
+/// 3) Pushes 'LHS ^ RHS' on the stack
+template <PrimType Name, class T = typename PrimConv<Name>::T>
+bool BitXor(InterpState &S, CodePtr OpPC) {
+  const T &RHS = S.Stk.pop<T>();
+  const T &LHS = S.Stk.pop<T>();
+
+  unsigned Bits = RHS.bitWidth();
+  T Result;
+  if (!T::bitXor(LHS, RHS, Bits, &Result)) {
+    S.Stk.push<T>(Result);
+    return true;
+  }
+  return false;
+}
+
+/// 1) Pops the RHS from the stack.
+/// 2) Pops the LHS from the stack.
 /// 3) Pushes 'LHS % RHS' on the stack (the remainder of dividing LHS by RHS).
 template <PrimType Name, class T = typename PrimConv<Name>::T>
 bool Rem(InterpState &S, CodePtr OpPC) {
   const T &RHS = S.Stk.pop<T>();
   const T &LHS = S.Stk.pop<T>();
 
   if (!CheckDivRem(S, OpPC, LHS, RHS))
     return false;

clang/lib/AST/Interp/Opcodes.td

 }
 
 def BitAnd : IntegerOpcode;
 def BitOr : IntegerOpcode;
 def Div : Opcode {
   let Types = [NumberTypeClass];
   let HasGroup = 1;
 }
+def BitXor : IntegerOpcode;
 
 //===----------------------------------------------------------------------===//
 // Unary operators.
 //===----------------------------------------------------------------------===//
 
 // [Real] -> [Real]
 def Inv: Opcode {
   let Types = [BoolTypeClass];

clang/test/AST/Interp/literals.cpp

namespace bitOr {
   static_assert((10 | 1) == 11, "");
   static_assert((10 | 10) == 10, "");
 
   static_assert((1337 | -1) == -1, "");
   static_assert((0 | gimme(12)) == 12, "");
   static_assert((12 | true) == 13, "");
 };
 
+namespace bitXor {
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wxor-used-as-pow"
+  static_assert((10 ^ 1) == 11, "");
+  static_assert((10 ^ 10) == 0, "");
+
+  enum {
+    ONE = 1,
+  };
+
+  static_assert((1337 ^ -1) == -1338, "");
+  static_assert((0 | gimme(12)) == 12, "");
+  static_assert((12 ^ true) == 13, "");
+  static_assert((12 ^ ONE) == 13, "");
+#pragma clang diagnostic pop
+};
+
 #if __cplusplus >= 201402L
 constexpr bool IgnoredUnary() {
   bool bo = true;
   !bo; // expected-warning {{expression result unused}} \
        // ref-warning {{expression result unused}}
   return bo;
 }
 static_assert(IgnoredUnary(), "");