[mlir][complex] Canonicalization for consecutive complex.neg

[Lewuathe]

Summary

Consecutive complex.neg are redundant so that we can canonicalize them to the original operands.

mlir/include/mlir/Dialect/Complex/IR/ComplexOps.td

let description = [{
     Example:
 
     ```mlir
     %a = complex.neg %b : complex<f32>
     ```
   }];
 
   let results = (outs Complex<AnyFloat>:$result);
+
+  let hasFolder = 1;
 }
 
 //===----------------------------------------------------------------------===//
 // NotEqualOp
 //===----------------------------------------------------------------------===//
 
 def NotEqualOp : Complex_Op<"neq",
     [NoSideEffect, AllTypesMatch<["lhs", "rhs"]>, Elementwise]> {

mlir/lib/Dialect/Complex/IR/ComplexOps.cpp

OpFoldResult AddOp::fold(ArrayRef<Attribute> operands) {
   if (auto sub = getRhs().getDefiningOp<SubOp>())
     if (getLhs() == sub.getRhs())
       return sub.getLhs();
 
   return {};
 }
 
 //===----------------------------------------------------------------------===//
+// NegOp
+//===----------------------------------------------------------------------===//
+
+OpFoldResult NegOp::fold(ArrayRef<Attribute> operands) {
+  assert(operands.size() == 1 && "unary op takes 1 operand");
+
+  // complex.neg(complex.neg(a)) -> a
+  if (auto negOp = getOperand().getDefiningOp<NegOp>())
+    return negOp.getOperand();
+
+  return {};
+}
+
+//===----------------------------------------------------------------------===//
 // TableGen'd op method definitions
 //===----------------------------------------------------------------------===//
 
 #define GET_OP_CLASSES
 #include "mlir/Dialect/Complex/IR/ComplexOps.cpp.inc"

mlir/test/Dialect/Complex/canonicalize.mlir

 func.func @complex_add_sub_rhs() -> complex<f32> {
   %complex1 = complex.constant [1.0 : f32, 0.0 : f32] : complex<f32>
   %complex2 = complex.constant [0.0 : f32, 2.0 : f32] : complex<f32>
   // CHECK: %[[CPLX:.*]] = complex.constant [1.000000e+00 : f32, 0.000000e+00 : f32] : complex<f32>
   // CHECK-NEXT: return %[[CPLX:.*]] : complex<f32>
   %sub = complex.sub %complex1, %complex2 : complex<f32>
   %add = complex.add %complex2, %sub : complex<f32>
   return %add : complex<f32>
+}
+
+// CHECK-LABEL: func @complex_neg_neg
+func.func @complex_neg_neg() -> complex<f32> {
+  %complex1 = complex.constant [1.0 : f32, 0.0 : f32] : complex<f32>
+  // CHECK: %[[CPLX:.*]] = complex.constant [1.000000e+00 : f32, 0.000000e+00 : f32] : complex<f32>
+  // CHECK-NEXT: return %[[CPLX:.*]] : complex<f32>
+  %neg1 = complex.neg %complex1 : complex<f32>
+  %neg2 = complex.neg %neg1 : complex<f32>
+  return %neg2 : complex<f32>
 }
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