[mlir][tosa] Fold consecutive negate as no-op

[Lewuathe]

Summary

Consecutive element-wise negate should be canonicalized as no-op.

[Lewuathe]

Add new line

[eric-k256]

LGTM.

mlir/include/mlir/Dialect/Tosa/IR/TosaOps.td

let arguments = (ins
       OptionalAttr<Tosa_UnaryOpQuantizationAttr>:$quantization_info
   );
 
   let results = (outs
     Tosa_Tensor:$output
   );
 
   let builders = [Tosa_UnaryOpQuantInfoBuilder];
+
+  let hasFolder = 1;
 }
 
 //===----------------------------------------------------------------------===//
 // Operator: reciprocal
 //===----------------------------------------------------------------------===//
 def Tosa_ReciprocalOp : Tosa_Op<"reciprocal", [
     DeclareOpInterfaceMethods<InferShapedTypeOpInterface,
                               ["inferReturnTypeComponents"]>,

mlir/lib/Dialect/Tosa/IR/TosaCanonicalizations.cpp

OpFoldResult tosa::ExpOp::fold(FoldAdaptor adaptor) {
   auto input = getInput1();
   // Element-wise exp(log(x)) = x
   if (auto op = input.getDefiningOp<tosa::LogOp>()) {
     return op.getInput1();
   }
 
   return {};
 }
+
+OpFoldResult tosa::NegateOp::fold(FoldAdaptor adaptor) {
+  auto input = getInput1();
+  // Element-wise negate(negate(x)) = x
+  if (auto op = input.getDefiningOp<tosa::NegateOp>()) {
+    return op.getInput1();
+  }
+
+  return {};
+}

mlir/test/Dialect/Tosa/canonicalize.mlir

 
 // CHECK-LABEL: @fold_exp_log
 func.func @fold_exp_log(%arg0: tensor<?x1xf32>) -> tensor<?x1xf32> {
   // CHECK: return %arg{{.*}} : tensor<?x1xf32>
   %0 = "tosa.log"(%arg0) : (tensor<?x1xf32>) -> tensor<?x1xf32>
   %1 = "tosa.exp"(%0) : (tensor<?x1xf32>) -> tensor<?x1xf32>
   return %1 : tensor<?x1xf32>
 }
+
+// -----
+
+// CHECK-LABEL: @fold_negate_negate
+func.func @fold_negate_negate(%arg0: tensor<?x1xf32>) -> tensor<?x1xf32> {
+  // CHECK: return %arg{{.*}} : tensor<?x1xf32>
+  %0 = "tosa.negate"(%arg0) : (tensor<?x1xf32>) -> tensor<?x1xf32>
+  %1 = "tosa.negate"(%0) : (tensor<?x1xf32>) -> tensor<?x1xf32>
+  return %1 : tensor<?x1xf32>
+}
+