message: Fix signedness for compiler
diff: @@ -102,7 +102,7 @@ void Gradient::ComputeOperandDerivs(mlir::Value* val) {
  } else if (auto reshape_op = mlir::dyn_cast<ReshapeOp>(op)) {
  auto tensor_input = reshape_op.tensor();
  std::vector<mlir::Value*> args{grads_[val]};
  - for (size_t i = 0; i < tensor_input->getType().dyn_cast<RankedTensorType>().getRank(); ++i) {
  + for (int i = 0; i < tensor_input->getType().dyn_cast<RankedTensorType>().getRank(); ++i) {
  args.push_back(builder_->MakeDimOp(tensor_input, i));
  }
  auto dop = builder_->MakePrimitiveOp("reshape", args);
  @@ -248,7 +248,7 @@ mlir::Value* Gradient::DeriveContraction(mlir::Value* dout, mlir::Value* out, si
  }
  auto target_src_op = llvm::cast<AffineTensorMapOp>(target_src->getDefiningOp());
  std::vector<mlir::Value*> sizes;
  - for (size_t i = 0; i < target_src_op.tensor()->getType().dyn_cast<RankedTensorType>().getRank(); ++i) {
  + for (int i = 0; i < target_src_op.tensor()->getType().dyn_cast<RankedTensorType>().getRank(); ++i) {
  sizes.push_back(builder_->MakeDimOp(target_src_op.tensor(), i));
  }
  std::vector<mlir::Value*> dsrc_idxs;
  