message: fix ptr->ptr bitcasts
  fixes regression in Transforms/InstSimplify/ptr_diff.ll
diff: @@ -916,18 +916,20 @@ StateValue ConversionOp::toSMT(State &s) const {
  return { move(v), sv.non_poison && np };
  };
  - if (op == BitCast)
  + if (op == BitCast) {
  + // NOP: ptr vect -> ptr vect
  + if (getType().isVectorType() &&
  + getType().getAsAggregateType()->getChild(0).isPtrType())
  + return v;
  +
  v = val->getType().toInt(s, move(v));
  + }
  if (getType().isVectorType()) {
  vector<StateValue> vals;
  auto retty = getType().getAsAggregateType();
  auto elems = retty->numElementsConst();
  - // NOP: ptr vect -> ptr vect
  - if (op == BitCast && retty->getChild(0).isPtrType())
  - return v;
  -
  // bitcast vect elems size may vary, so create a new data type whose
  // element size is aligned with the output vector elem size
  IntType elem_ty("int", retty->bits() / elems);
  