[mlir][Arithmetic] fold overlapping negf.

[jacquesguan]

Summary

This patch folds negf(negf(x)) to x.

mlir/lib/Dialect/Arithmetic/IR/ArithmeticOps.cpp

void arith::XOrIOp::getCanonicalizationPatterns(
   patterns.add<XOrINotCmpI>(context);
 }
 
 //===----------------------------------------------------------------------===//
 // NegFOp
 //===----------------------------------------------------------------------===//
 
 OpFoldResult arith::NegFOp::fold(ArrayRef<Attribute> operands) {
+  /// negf(negf(x)) -> x
+  if (auto op = this->getOperand().getDefiningOp<arith::NegFOp>())
+    return op.getOperand();
   return constFoldUnaryOp<FloatAttr>(operands,
                                      [](const APFloat &a) { return -a; });
 }
 
 //===----------------------------------------------------------------------===//
 // AddFOp
 //===----------------------------------------------------------------------===//
 

mlir/test/Dialect/Arithmetic/canonicalize.mlir

 // CHECK: %[[res:.+]] = arith.constant -2.0
 // CHECK: return %[[res]]
 func.func @test_negf() -> (f32) {
   %c = arith.constant 2.0 : f32
   %0 = arith.negf %c : f32
   return %0: f32
 }
 
+// CHECK-LABEL: @test_negf1(
+// CHECK-SAME: %[[arg0:.+]]:
+// CHECK: return %[[arg0]]
+func.func @test_negf1(%f : f32) -> (f32) {
+  %0 = arith.negf %f : f32
+  %1 = arith.negf %0 : f32
+  return %1: f32
+}
+
 // -----
 
 // CHECK-LABEL: @test_remui(
 // CHECK: %[[res:.+]] = arith.constant dense<[0, 0, 4, 2]> : vector<4xi32>
 // CHECK: return %[[res]]
 func.func @test_remui() -> (vector<4xi32>) {
   %v1 = arith.constant dense<[9, 9, 9, 9]> : vector<4xi32>
   %v2 = arith.constant dense<[1, 3, 5, 7]> : vector<4xi32>