[mlir][arith] Use declarative asm format for fastmath flags

[rkayaith]

Summary

Switch to using an optional group in the assembly format instead of a
custom directive. There's no change to the actual printed format.

[vzakhari]

Thank you for the clean-up!

mlir/include/mlir/Dialect/Arith/IR/ArithOps.td

 // Base class for floating point unary operations.
 class Arith_FloatUnaryOp<string mnemonic, list<Trait> traits = []> :
     Arith_UnaryOp<mnemonic,
       !listconcat([DeclareOpInterfaceMethods<ArithFastMathInterface>],
                   traits)>,
     Arguments<(ins FloatLike:$operand,
       DefaultValuedAttr<Arith_FastMathAttr, "FastMathFlags::none">:$fastmath)>,
     Results<(outs FloatLike:$result)> {
-  let assemblyFormat = [{ $operand custom<ArithFastMathAttr>($fastmath)
+  let assemblyFormat = [{ $operand (`fastmath` `` $fastmath^)?
                           attr-dict `:` type($result) }];
 }
 
 // Base class for floating point binary operations.
 class Arith_FloatBinaryOp<string mnemonic, list<Trait> traits = []> :
     Arith_BinaryOp<mnemonic,
       !listconcat([DeclareOpInterfaceMethods<ArithFastMathInterface>],
                   traits)>,
     Arguments<(ins FloatLike:$lhs, FloatLike:$rhs,
       DefaultValuedAttr<Arith_FastMathAttr, "FastMathFlags::none">:$fastmath)>,
     Results<(outs FloatLike:$result)> {
-  let assemblyFormat = [{ $lhs `,` $rhs `` custom<ArithFastMathAttr>($fastmath)
+  let assemblyFormat = [{ $lhs `,` $rhs (`fastmath` `` $fastmath^)?
                           attr-dict `:` type($result) }];
 }
 
 // Base class for arithmetic cast operations. Requires a single operand and
 // result. If either is a shaped type, then the other must be of the same shape.
 class Arith_CastOp<string mnemonic, TypeConstraint From, TypeConstraint To,
                    list<Trait> traits = []> :
     Arith_Op<mnemonic, traits # [SameOperandsAndResultShape,

mlir/lib/Dialect/Arith/IR/ArithOps.cpp

 
 #include "llvm/ADT/APSInt.h"
 #include "llvm/ADT/SmallString.h"
 
 using namespace mlir;
 using namespace mlir::arith;
 
 //===----------------------------------------------------------------------===//
-// Floating point op parse/print helpers
-//===----------------------------------------------------------------------===//
-static ParseResult parseArithFastMathAttr(OpAsmParser &parser,
-                                          Attribute &attr) {
-  if (succeeded(
-          parser.parseOptionalKeyword(FastMathFlagsAttr::getMnemonic()))) {
-    attr = FastMathFlagsAttr::parse(parser, Type{});
-    return success(static_cast<bool>(attr));
-  } else {
-    // No fastmath attribute mnemonic present - defer attribute creation and use
-    // the default value.
-    return success();
-  }
-}
-
-static void printArithFastMathAttr(OpAsmPrinter &printer, Operation *op,
-                                   FastMathFlagsAttr fmAttr) {
-  // Elide printing the fastmath attribute when fastmath=none
-  if (fmAttr && (fmAttr.getValue() != FastMathFlags::none)) {
-    printer << " " << FastMathFlagsAttr::getMnemonic();
-    fmAttr.print(printer);
-  }
-}
-
-//===----------------------------------------------------------------------===//
 // Pattern helpers
 //===----------------------------------------------------------------------===//
 
 static IntegerAttr addIntegerAttrs(PatternRewriter &builder, Value res,
                                    Attribute lhs, Attribute rhs) {
   return builder.getIntegerAttr(res.getType(),
                                 lhs.cast<IntegerAttr>().getInt() +
                                     rhs.cast<IntegerAttr>().getInt());