[mlir][complex] Canonicalization for complex.sub adding same numbers

[Lewuathe]

Summary

Canonicalization for complex.sub adding same numbers. This canonicalization supports the case like complex.sub(complex.add(a, b), b) -> a.

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

let description = [{
     The `sub` operation takes two complex numbers and returns their difference.
 
     Example:
 
     ```mlir
     %a = complex.sub %b, %c : complex<f32>
     ```
   }];
+
+  let hasFolder = 1;
 }
 
 //===----------------------------------------------------------------------===//
 // TanhOp
 //===----------------------------------------------------------------------===//
 
 def TanhOp : ComplexUnaryOp<"tanh", [SameOperandsAndResultType]> {
   let summary = "complex hyperbolic tangent";

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

if (arrayAttr[0].cast<FloatAttr>().getValue().isZero() &&
       return getLhs();
     }
   }
 
   return {};
 }
 
 //===----------------------------------------------------------------------===//
+// SubOp
+//===----------------------------------------------------------------------===//
+
+OpFoldResult SubOp::fold(ArrayRef<Attribute> operands) {
+  assert(operands.size() == 2 && "binary op takes 2 operands");
+
+  // complex.sub(complex.add(a, b), b) -> a
+  if (auto add = getLhs().getDefiningOp<AddOp>())
+    if (getRhs() == add.getRhs())
+      return add.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>())

mlir/test/Dialect/Complex/canonicalize.mlir

 // CHECK-LABEL: func @complex_add_zero
 func.func @complex_add_zero() -> complex<f32> {
   %complex1 = complex.constant [1.0 : f32, 0.0 : f32] : complex<f32>
   %complex2 = complex.constant [0.0 : 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>
   %add = complex.add %complex1, %complex2 : complex<f32>
   return %add : complex<f32>
+}
+
+// CHECK-LABEL: func @complex_sub_add_lhs
+func.func @complex_sub_add_lhs() -> 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>
+  %add = complex.add %complex1, %complex2 : complex<f32>
+  %sub = complex.sub %add, %complex2 : complex<f32>
+  return %sub : complex<f32>
 }
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