def SplatB: SDNodeXForm<imm, [{
  uint32_t V = N->getZExtValue();
  assert(isUInt<8>(V) || V >> 8 == 0xFFFFFF);
  uint32_t S = V << 24 | V << 16 | V << 8 | V;
  V &= 0xFF;
  return CurDAG->getTargetConstant(S, SDLoc(N), MVT::i32);
}]>;

clang static analyzer reports this as a dead store - but isn't the problem that we need to mask V's bottom 8 bits before S 'splats' it across the 32-bits:

def SplatB: SDNodeXForm<imm, [{
  uint32_t V = N->getZExtValue();
  assert(isUInt<8>(V) || V >> 8 == 0xFFFFFF);
  V &= 0xFF;
  uint32_t S = V << 24 | V << 16 | V << 8 | V;
  return CurDAG->getTargetConstant(S, SDLoc(N), MVT::i32);
}]>;