[mlir][tosa] Fold exp(log) operation into no-op

[Lewuathe]

Summary

Element-wise exp(log) can be canonicalized as no-op.

[eric-k256]

LGTM.

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

def Tosa_ExpOp : Tosa_Op<"exp", [
 
   let arguments = (ins
     Tosa_Tensor:$input1
   );
 
   let results = (outs
     Tosa_Tensor:$output
   );
+
+  let hasFolder = 1;
 }
 
 //===----------------------------------------------------------------------===//
 // Operator: floor
 //===----------------------------------------------------------------------===//
 def Tosa_FloorOp : Tosa_Op<"floor", [
     DeclareOpInterfaceMethods<InferShapedTypeOpInterface,
                               ["inferReturnTypeComponents"]>,

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

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

mlir/test/Dialect/Tosa/canonicalize.mlir

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