[cleanup] Fix a few more llvm::None -> std::nullopt

include/torch-mlir/Dialect/Torch/Utils/Utils.h

@@ -61,7 +61,7 @@ Value convertTensorToDtype(PatternRewriter &rewriter, Location loc, Value input,
 bool isBuiltInType(Type type);
 
 // Helper funtion to get rank of `Base tensor type`.
-// llvm::None is returned if the tensorRank can't be determined.
+// std::nullopt is returned if the tensorRank can't be determined.
 Optional<unsigned> getTensorRank(Value tensor);
 
 bool isViewLikeOp(Operation *op);

lib/Conversion/TorchToMhlo/MhloLegalizeUtils.cpp

@@ -58,7 +58,7 @@ llvm::Optional<Value> getConstTensor(PatternRewriter &rewriter, Operation *op,
 
   if (vec.size() != num_total_elements) {
     op->emitOpError("getConstTensor(): number of elements mismatch.");
-    return llvm::None;
+    return std::nullopt;
   }
 
   auto const_type =
@@ -82,7 +82,7 @@ llvm::Optional<Value> getConstTensor<APInt>(PatternRewriter &rewriter,
 
   if (vec.size() != num_total_elements) {
     op->emitOpError("getConstTensor(): number of elements mismatch.");
-    return llvm::None;
+    return std::nullopt;
   }
   auto const_type = RankedTensorType::get(
       shape, rewriter.getIntegerType(vec[0].getBitWidth()));
@@ -105,7 +105,7 @@ llvm::Optional<Value> getConstTensor<float>(PatternRewriter &rewriter,
 
   if (vec.size() != num_total_elements) {
     op->emitOpError("getConstTensor(): number of elements mismatch.");
-    return llvm::None;
+    return std::nullopt;
   }
 
   auto const_type = RankedTensorType::get(shape, rewriter.getF32Type());
@@ -127,7 +127,7 @@ getConstTensor<double>(PatternRewriter &rewriter, Operation *op,
 
   if (vec.size() != num_total_elements) {
     op->emitOpError("getConstTensor(): number of elements mismatch.");
-    return llvm::None;
+    return std::nullopt;
   }
 
   auto const_type = RankedTensorType::get(shape, rewriter.getF64Type());

lib/Conversion/TorchToMhlo/Reduction.cpp

@@ -77,16 +77,17 @@ getMaxInDim(ConversionPatternRewriter &rewriter, Operation *op, Value &input,
             size_t dimSizeIndexBits) {
   auto inputTy = input.getType().template cast<RankedTensorType>();
   if (!inputTy) {
-    return llvm::None;
+    return std::nullopt;
   }
   if (!inputTy.getElementType().isIntOrFloat()) {
-    return llvm::None;
+    return std::nullopt;
   }
   auto inputShape = inputTy.getShape();
   auto inputElemTy = inputTy.getElementType();
 
   Value initValue = createInitialValueForReduceOp(op, inputElemTy, rewriter);
-  if (!initValue) return llvm::None;
+  if (!initValue)
+    return std::nullopt;
   Value initIndex;
   if (dimSizeIndexBits == 32) {
     initIndex = mhlo::getConstTensor<int32_t>(rewriter, op, {0}, {}).value();

lib/Conversion/TorchToMhlo/ViewLike.cpp

@@ -269,7 +269,7 @@ LogicalResult ConvertAtenOp<AtenSliceTensorOp>::matchAndRewrite(
 
   auto getOptionalVal = [&](Value val) -> llvm::Optional<Value> {
     if (val.getType().isa<Torch::NoneType>()) {
-      return llvm::None;
+      return std::nullopt;
     } else {
       return val;
     }