[mlir] Migrate away from std::nullopt (NFC) (#145842)

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 replaces {} with std::nullopt.

Author: kazutakahirata

mlir/include/mlir/Dialect/LLVMIR/LLVMOpBase.td

@@ -235,8 +235,7 @@ class LLVM_MemOpPatterns {
   }];
   code setInvariantGroupCode = [{
     if ($invariantGroup) {
-      llvm::MDNode *metadata = llvm::MDNode::get(inst->getContext(),
-                                                 std::nullopt);
+      llvm::MDNode *metadata = llvm::MDNode::get(inst->getContext(), {});
       inst->setMetadata(llvm::LLVMContext::MD_invariant_group, metadata);
     }
   }];

mlir/include/mlir/Dialect/LLVMIR/LLVMOps.td

@@ -425,7 +425,7 @@ def LLVM_LoadOp : LLVM_MemAccessOpBase<"load",
     auto *inst = builder.CreateLoad($_resultType, $addr, $volatile_);
     $res = inst;
     if ($invariant) {
-      llvm::MDNode *metadata = llvm::MDNode::get(inst->getContext(), std::nullopt);
+      llvm::MDNode *metadata = llvm::MDNode::get(inst->getContext(), {});
       inst->setMetadata(llvm::LLVMContext::MD_invariant_load, metadata);
     }
     if ($dereferenceable)

mlir/include/mlir/IR/Matchers.h

@@ -88,7 +88,7 @@ struct constant_op_binder {
 
     // Fold the constant to an attribute.
     SmallVector<OpFoldResult, 1> foldedOp;
-    LogicalResult result = op->fold(/*operands=*/std::nullopt, foldedOp);
+    LogicalResult result = op->fold(/*operands=*/{}, foldedOp);
     (void)result;
     assert(succeeded(result) && "expected ConstantLike op to be foldable");
 

mlir/include/mlir/IR/PatternMatch.h

@@ -810,8 +810,7 @@ class RewritePatternSet {
   RewritePatternSet &add(ConstructorArg &&arg, ConstructorArgs &&...args) {
     // The following expands a call to emplace_back for each of the pattern
     // types 'Ts'.
-    (addImpl<Ts>(/*debugLabels=*/std::nullopt,
-                 std::forward<ConstructorArg>(arg),
+    (addImpl<Ts>(/*debugLabels=*/{}, std::forward<ConstructorArg>(arg),
                  std::forward<ConstructorArgs>(args)...),
      ...);
     return *this;
@@ -894,7 +893,7 @@ class RewritePatternSet {
   RewritePatternSet &insert(ConstructorArg &&arg, ConstructorArgs &&...args) {
     // The following expands a call to emplace_back for each of the pattern
     // types 'Ts'.
-    (addImpl<Ts>(/*debugLabels=*/std::nullopt, arg, args...), ...);
+    (addImpl<Ts>(/*debugLabels=*/{}, arg, args...), ...);
     return *this;
   }
 

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

@@ -903,8 +903,8 @@ class UserConstraintDecl final
                                         ArrayRef<VariableDecl *> results,
                                         const CompoundStmt *body,
                                         Type resultType) {
-    return createImpl(ctx, name, inputs, /*nativeInputTypes=*/std::nullopt,
-                      results, /*codeBlock=*/std::nullopt, body, resultType);
+    return createImpl(ctx, name, inputs, /*nativeInputTypes=*/{}, results,
+                      /*codeBlock=*/std::nullopt, body, resultType);
   }
 
   /// Return the name of the constraint.

mlir/lib/Dialect/Async/IR/Async.cpp

@@ -309,7 +309,7 @@ void FuncOp::build(OpBuilder &builder, OperationState &state, StringRef name,
     return;
   assert(type.getNumInputs() == argAttrs.size());
   call_interface_impl::addArgAndResultAttrs(
-      builder, state, argAttrs, /*resultAttrs=*/std::nullopt,
+      builder, state, argAttrs, /*resultAttrs=*/{},
       getArgAttrsAttrName(state.name), getResAttrsAttrName(state.name));
 }
 

mlir/lib/Dialect/EmitC/IR/EmitC.cpp

@@ -601,7 +601,7 @@ void FuncOp::build(OpBuilder &builder, OperationState &state, StringRef name,
     return;
   assert(type.getNumInputs() == argAttrs.size());
   call_interface_impl::addArgAndResultAttrs(
-      builder, state, argAttrs, /*resultAttrs=*/std::nullopt,
+      builder, state, argAttrs, /*resultAttrs=*/{},
       getArgAttrsAttrName(state.name), getResAttrsAttrName(state.name));
 }
 

mlir/lib/Dialect/Func/IR/FuncOps.cpp

@@ -193,7 +193,7 @@ void FuncOp::build(OpBuilder &builder, OperationState &state, StringRef name,
     return;
   assert(type.getNumInputs() == argAttrs.size());
   call_interface_impl::addArgAndResultAttrs(
-      builder, state, argAttrs, /*resultAttrs=*/std::nullopt,
+      builder, state, argAttrs, /*resultAttrs=*/{},
       getArgAttrsAttrName(state.name), getResAttrsAttrName(state.name));
 }
 

mlir/lib/Dialect/LLVMIR/IR/LLVMDialect.cpp

@@ -2774,7 +2774,7 @@ void LLVMFuncOp::build(OpBuilder &builder, OperationState &result,
   assert(llvm::cast<LLVMFunctionType>(type).getNumParams() == argAttrs.size() &&
          "expected as many argument attribute lists as arguments");
   call_interface_impl::addArgAndResultAttrs(
-      builder, result, argAttrs, /*resultAttrs=*/std::nullopt,
+      builder, result, argAttrs, /*resultAttrs=*/{},
       getArgAttrsAttrName(result.name), getResAttrsAttrName(result.name));
 }
 

mlir/lib/Dialect/Shape/IR/Shape.cpp

@@ -1303,7 +1303,7 @@ void FuncOp::build(OpBuilder &builder, OperationState &state, StringRef name,
     return;
   assert(type.getNumInputs() == argAttrs.size());
   call_interface_impl::addArgAndResultAttrs(
-      builder, state, argAttrs, /*resultAttrs=*/std::nullopt,
+      builder, state, argAttrs, /*resultAttrs=*/{},
       getArgAttrsAttrName(state.name), getResAttrsAttrName(state.name));
 }