[mlir] Migrate away from ArrayRef(std::nullopt) (NFC) (#144989)

ArrayRef has a constructor that accepts std::nullopt.  This
constructor dates back to the days when we still had llvm::Optional.

Since the use of std::nullopt outside the context of std::optional is
kind of abuse and not intuitive to new comers, I would like to move
away from the constructor and eventually remove it.

This patch takes care of the mlir side of the migration, starting with
straightforward places where I see ArrayRef or ValueRange nearby.
Note that ValueRange has a constructor that forwards arguments to an
ArrayRef constructor.

Author: kazutakahirata

mlir/include/mlir/AsmParser/AsmParserState.h

@@ -195,7 +195,7 @@ class AsmParserState {
   /// Finalize the most recently started operation definition.
   void finalizeOperationDefinition(
       Operation *op, SMRange nameLoc, SMLoc endLoc,
-      ArrayRef<std::pair<unsigned, SMLoc>> resultGroups = std::nullopt);
+      ArrayRef<std::pair<unsigned, SMLoc>> resultGroups = {});
 
   /// Start a definition for a region nested under the current operation.
   void startRegionDefinition();

mlir/include/mlir/Dialect/Linalg/Utils/Utils.h

@@ -94,7 +94,7 @@ bool isReductionIterator(utils::IteratorType iteratorType);
 /// ```
 Value makeComposedPadHighOp(OpBuilder &b, Location loc, RankedTensorType type,
                             Value source, Value padding, bool nofold,
-                            ValueRange typeDynDims = std::nullopt);
+                            ValueRange typeDynDims = {});
 
 /// Returns GenericOp that copies an n-D memref. Unlike the current
 /// implementation of memref::CopyOp, this op can further tile, lower to loops

mlir/include/mlir/Dialect/Tensor/Utils/Utils.h

@@ -30,7 +30,7 @@ namespace tensor {
 // for _static_ dimensions.
 PadOp createPadHighOp(RankedTensorType resType, Value source, Value pad,
                       bool nofold, Location loc, OpBuilder &builder,
-                      ValueRange dynOutDims = std::nullopt);
+                      ValueRange dynOutDims = {});
 
 // Creates dim ops for each dynamic dimension of the ranked tensor argument and
 // returns these as values.

mlir/include/mlir/ExecutionEngine/ExecutionEngine.h

@@ -157,8 +157,7 @@ class ExecutionEngine {
 
   /// Invokes the function with the given name passing it the list of opaque
   /// pointers to the actual arguments.
-  llvm::Error invokePacked(StringRef name,
-                           MutableArrayRef<void *> args = std::nullopt);
+  llvm::Error invokePacked(StringRef name, MutableArrayRef<void *> args = {});
 
   /// Trait that defines how a given type is passed to the JIT code. This
   /// defaults to passing the address but can be specialized.

mlir/include/mlir/IR/BlockSupport.h

@@ -106,7 +106,7 @@ class BlockRange final
           Block *, Block *, Block *> {
 public:
   using RangeBaseT::RangeBaseT;
-  BlockRange(ArrayRef<Block *> blocks = std::nullopt);
+  BlockRange(ArrayRef<Block *> blocks = {});
   BlockRange(SuccessorRange successors);
   template <typename Arg, typename = std::enable_if_t<std::is_constructible<
                               ArrayRef<Block *>, Arg>::value>>

mlir/include/mlir/IR/Builders.h

@@ -454,15 +454,14 @@ class OpBuilder : public Builder {
   /// 'parent'. `locs` contains the locations of the inserted arguments, and
   /// should match the size of `argTypes`.
   Block *createBlock(Region *parent, Region::iterator insertPt = {},
-                     TypeRange argTypes = std::nullopt,
-                     ArrayRef<Location> locs = std::nullopt);
+                     TypeRange argTypes = {}, ArrayRef<Location> locs = {});
 
   /// Add new block with 'argTypes' arguments and set the insertion point to the
   /// end of it. The block is placed before 'insertBefore'. `locs` contains the
   /// locations of the inserted arguments, and should match the size of
   /// `argTypes`.
-  Block *createBlock(Block *insertBefore, TypeRange argTypes = std::nullopt,
-                     ArrayRef<Location> locs = std::nullopt);
+  Block *createBlock(Block *insertBefore, TypeRange argTypes = {},
+                     ArrayRef<Location> locs = {});
 
   //===--------------------------------------------------------------------===//
   // Operation Creation

mlir/include/mlir/IR/BuiltinTypes.td

@@ -1200,7 +1200,7 @@ def Builtin_UnrankedMemRef : Builtin_Type<"UnrankedMemRef", "unranked_memref", [
     using ShapedType::Trait<UnrankedMemRefType>::getDimSize;
     using ShapedType::Trait<UnrankedMemRefType>::getDynamicDimIndex;
 
-    ArrayRef<int64_t> getShape() const { return std::nullopt; }
+    ArrayRef<int64_t> getShape() const { return {}; }
 
     /// [deprecated] Returns the memory space in old raw integer representation.
     /// New `Attribute getMemorySpace()` method should be used instead.
@@ -1259,7 +1259,7 @@ def Builtin_UnrankedTensor : Builtin_Type<"UnrankedTensor", "unranked_tensor", [
     using ShapedType::Trait<UnrankedTensorType>::getDimSize;
     using ShapedType::Trait<UnrankedTensorType>::getDynamicDimIndex;
 
-    ArrayRef<int64_t> getShape() const { return std::nullopt; }
+    ArrayRef<int64_t> getShape() const { return {}; }
   }];
   let skipDefaultBuilders = 1;
   let genVerifyDecl = 1;

mlir/include/mlir/IR/PatternMatch.h

@@ -520,7 +520,7 @@ class RewriterBase : public OpBuilder {
   /// unreachable operations.
   virtual void inlineBlockBefore(Block *source, Block *dest,
                                  Block::iterator before,
-                                 ValueRange argValues = std::nullopt);
+                                 ValueRange argValues = {});
 
   /// Inline the operations of block 'source' before the operation 'op'. The
   /// source block will be deleted and must have no uses. 'argValues' is used to
@@ -529,16 +529,15 @@ class RewriterBase : public OpBuilder {
   /// The source block must have no successors. Otherwise, the resulting IR
   /// would have unreachable operations.
   void inlineBlockBefore(Block *source, Operation *op,
-                         ValueRange argValues = std::nullopt);
+                         ValueRange argValues = {});
 
   /// Inline the operations of block 'source' into the end of block 'dest'. The
   /// source block will be deleted and must have no uses. 'argValues' is used to
   /// replace the block arguments of 'source'
   ///
   /// The dest block must have no successors. Otherwise, the resulting IR would
   /// have unreachable operation.
-  void mergeBlocks(Block *source, Block *dest,
-                   ValueRange argValues = std::nullopt);
+  void mergeBlocks(Block *source, Block *dest, ValueRange argValues = {});
 
   /// Split the operations starting at "before" (inclusive) out of the given
   /// block into a new block, and return it.

mlir/include/mlir/IR/Region.h

@@ -353,7 +353,7 @@ class RegionRange
 public:
   using RangeBaseT::RangeBaseT;
 
-  RegionRange(MutableArrayRef<Region> regions = std::nullopt);
+  RegionRange(MutableArrayRef<Region> regions = {});
 
   template <typename Arg, typename = std::enable_if_t<std::is_constructible<
                               ArrayRef<std::unique_ptr<Region>>, Arg>::value>>

mlir/include/mlir/IR/SymbolTable.h

@@ -411,7 +411,8 @@ class SymbolUserMap {
   /// Return the users of the provided symbol operation.
   ArrayRef<Operation *> getUsers(Operation *symbol) const {
     auto it = symbolToUsers.find(symbol);
-    return it != symbolToUsers.end() ? it->second.getArrayRef() : std::nullopt;
+    return it != symbolToUsers.end() ? it->second.getArrayRef()
+                                     : ArrayRef<Operation *>();
   }
 
   /// Return true if the given symbol has no uses.

mlir/include/mlir/IR/TypeRange.h

@@ -37,7 +37,7 @@ class TypeRange : public llvm::detail::indexed_accessor_range_base<
                       Type, Type, Type> {
 public:
   using RangeBaseT::RangeBaseT;
-  TypeRange(ArrayRef<Type> types = std::nullopt);
+  TypeRange(ArrayRef<Type> types = {});
   explicit TypeRange(OperandRange values);
   explicit TypeRange(ResultRange values);
   explicit TypeRange(ValueRange values);

mlir/include/mlir/IR/ValueRange.h

@@ -126,7 +126,7 @@ class MutableOperandRange {
   /// and range length. `operandSegments` is an optional set of operand segments
   /// to be updated when mutating the operand list.
   MutableOperandRange(Operation *owner, unsigned start, unsigned length,
-                      ArrayRef<OperandSegment> operandSegments = std::nullopt);
+                      ArrayRef<OperandSegment> operandSegments = {});
   MutableOperandRange(Operation *owner);
 
   /// Construct a new mutable range for the given OpOperand.
@@ -409,7 +409,7 @@ class ValueRange final
       : ValueRange(ResultRange(values)) {}
   ValueRange(ArrayRef<BlockArgument> values)
       : ValueRange(ArrayRef<Value>(values.data(), values.size())) {}
-  ValueRange(ArrayRef<Value> values = std::nullopt);
+  ValueRange(ArrayRef<Value> values = {});
   ValueRange(OperandRange values);
   ValueRange(ResultRange values);
 

mlir/include/mlir/Rewrite/FrozenRewritePatternSet.h

@@ -47,10 +47,9 @@ class FrozenRewritePatternSet {
   /// `RewritePatternSet::addWithLabel`. Debug names may be empty, but patterns
   /// created with `RewritePattern::create` have their default debug name set to
   /// their type name.
-  FrozenRewritePatternSet(
-      RewritePatternSet &&patterns,
-      ArrayRef<std::string> disabledPatternLabels = std::nullopt,
-      ArrayRef<std::string> enabledPatternLabels = std::nullopt);
+  FrozenRewritePatternSet(RewritePatternSet &&patterns,
+                          ArrayRef<std::string> disabledPatternLabels = {},
+                          ArrayRef<std::string> enabledPatternLabels = {});
 
   /// Return the op specific native patterns held by this list.
   const OpSpecificNativePatternListT &getOpSpecificNativePatterns() const {

mlir/include/mlir/Tools/PDLL/AST/Types.h

@@ -226,8 +226,7 @@ class TupleType : public Type::TypeBase<detail::TupleTypeStorage> {
   /// Return an instance of the Tuple type.
   static TupleType get(Context &context, ArrayRef<Type> elementTypes,
                        ArrayRef<StringRef> elementNames);
-  static TupleType get(Context &context,
-                       ArrayRef<Type> elementTypes = std::nullopt);
+  static TupleType get(Context &context, ArrayRef<Type> elementTypes = {});
 
   /// Return the element types of this tuple.
   ArrayRef<Type> getElementTypes() const;

mlir/include/mlir/Transforms/DialectConversion.h

@@ -826,7 +826,7 @@ class ConversionPatternRewriter final : public PatternRewriter {
 
   /// PatternRewriter hook for inlining the ops of a block into another block.
   void inlineBlockBefore(Block *source, Block *dest, Block::iterator before,
-                         ValueRange argValues = std::nullopt) override;
+                         ValueRange argValues = {}) override;
   using PatternRewriter::inlineBlockBefore;
 
   /// PatternRewriter hook for updating the given operation in-place.

mlir/include/mlir/Transforms/Passes.h

@@ -62,8 +62,8 @@ std::unique_ptr<Pass> createCanonicalizerPass();
 /// set to their type name.
 std::unique_ptr<Pass>
 createCanonicalizerPass(const GreedyRewriteConfig &config,
-                        ArrayRef<std::string> disabledPatterns = std::nullopt,
-                        ArrayRef<std::string> enabledPatterns = std::nullopt);
+                        ArrayRef<std::string> disabledPatterns = {},
+                        ArrayRef<std::string> enabledPatterns = {});
 
 /// Creates a pass to perform control-flow sinking.
 std::unique_ptr<Pass> createControlFlowSinkPass();

mlir/lib/Dialect/GPU/Transforms/DecomposeMemRefs.cpp

@@ -55,7 +55,7 @@ static bool isInsideLaunch(Operation *op) {
 static std::tuple<Value, OpFoldResult, SmallVector<OpFoldResult>>
 getFlatOffsetAndStrides(OpBuilder &rewriter, Location loc, Value source,
                         ArrayRef<OpFoldResult> subOffsets,
-                        ArrayRef<OpFoldResult> subStrides = std::nullopt) {
+                        ArrayRef<OpFoldResult> subStrides = {}) {
   auto sourceType = cast<MemRefType>(source.getType());
   auto sourceRank = static_cast<unsigned>(sourceType.getRank());
 

mlir/lib/Dialect/LLVMIR/IR/TypeDetail.h

@@ -69,7 +69,7 @@ struct LLVMStructTypeStorage : public TypeStorage {
   class Key {
   public:
     /// Constructs a key for an identified struct.
-    Key(StringRef name, bool opaque, ArrayRef<Type> types = std::nullopt)
+    Key(StringRef name, bool opaque, ArrayRef<Type> types = {})
         : types(types), name(name), identified(true), packed(false),
           opaque(opaque) {}
     /// Constructs a key for a literal struct.

mlir/lib/Pass/PassStatistics.cpp

@@ -27,7 +27,7 @@ struct Statistic {
 
 /// Utility to print a pass entry in the statistics output.
 static void printPassEntry(raw_ostream &os, unsigned indent, StringRef pass,
-                           MutableArrayRef<Statistic> stats = std::nullopt) {
+                           MutableArrayRef<Statistic> stats = {}) {
   os.indent(indent) << pass << "\n";
   if (stats.empty())
     return;

mlir/unittests/IR/OperationSupportTest.cpp

@@ -18,9 +18,8 @@
 using namespace mlir;
 using namespace mlir::detail;
 
-static Operation *createOp(MLIRContext *context,
-                           ArrayRef<Value> operands = std::nullopt,
-                           ArrayRef<Type> resultTypes = std::nullopt,
+static Operation *createOp(MLIRContext *context, ArrayRef<Value> operands = {},
+                           ArrayRef<Type> resultTypes = {},
                            unsigned int numRegions = 0) {
   context->allowUnregisteredDialects();
   return Operation::create(

mlir/unittests/IR/ValueTest.cpp

@@ -16,9 +16,8 @@
 
 using namespace mlir;
 
-static Operation *createOp(MLIRContext *context,
-                           ArrayRef<Value> operands = std::nullopt,
-                           ArrayRef<Type> resultTypes = std::nullopt,
+static Operation *createOp(MLIRContext *context, ArrayRef<Value> operands = {},
+                           ArrayRef<Type> resultTypes = {},
                            unsigned int numRegions = 0) {
   context->allowUnregisteredDialects();
   return Operation::create(