[mlir][complex] Canonicalize consecutive complex.conj

[Lewuathe]

Summary

We can canonicalize consecutive complex.conj just by removing all conjugate operations.

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

let description = [{
     Example:
 
     ```mlir
     %a = complex.conj %b: complex<f32>
     ```
   }];
 
   let results = (outs Complex<AnyFloat>:$result);
+  let hasFolder = 1;
 }
 
 //===----------------------------------------------------------------------===//
 // AngleOp
 //===----------------------------------------------------------------------===//
 
 def AngleOp : ComplexUnaryOp<"angle",
                            [TypesMatchWith<"complex element type matches result type",

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

OpFoldResult ExpOp::fold(ArrayRef<Attribute> operands) {
   // complex.exp(complex.log(a)) -> a
   if (auto logOp = getOperand().getDefiningOp<LogOp>())
     return logOp.getOperand();
 
   return {};
 }
 
 //===----------------------------------------------------------------------===//
+// ConjOp
+//===----------------------------------------------------------------------===//
+
+OpFoldResult ConjOp::fold(ArrayRef<Attribute> operands) {
+  assert(operands.size() == 1 && "unary op takes 1 operand");
+
+  // complex.conj(complex.conj(a)) -> a
+  if (auto conjOp = getOperand().getDefiningOp<ConjOp>())
+    return conjOp.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

 // CHECK-LABEL: func @complex_exp_log
 func.func @complex_exp_log() -> 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>
   %log = complex.log %complex1 : complex<f32>
   %exp = complex.exp %log : complex<f32>
   return %exp : complex<f32>
+}
+
+// CHECK-LABEL: func @complex_conj_conj
+func.func @complex_conj_conj() -> 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>
+  %conj1 = complex.conj %complex1 : complex<f32>
+  %conj2 = complex.conj %conj1 : complex<f32>
+  return %conj2 : complex<f32>
 }
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