message: [XLA:SPMD] Pass user sharding to Pad when the instruction is the first operand
  only.
diff: @@ -1302,6 +1302,9 @@ absl::optional<HloSharding> GetShardingFromUser(
  user.shape(), instruction.shape(), user.sharding());
  }
  case HloOpcode::kPad: {
  + if (&instruction != user.operand(0)) {
  + return absl::nullopt;
  + }
  return user.sharding();
  }
  case HloOpcode::kSlice: {
  