[mlir][tosa] Remove log(exp(x)) and exp(log(x)) folders (llvm#156434)

Both of the folders would reduce to `x`. These folders were vulnerable
to overflow / underflow issues, resulting in a difference in numerical
behaviour when running or not running the folders. For now they have
been removed. We can consider restoring these as part of an optional and
separate "fast-math" style of transformation in the future.

Author: lhutton1

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

@@ -1331,8 +1331,6 @@ def Tosa_ExpOp : Tosa_ElementwiseUnaryOp<"exp"> {
     Extension<[Tosa_EXT_BF16]>,
   ];
 
-  let hasFolder = 1;
-
   let assemblyFormat = "operands attr-dict `:` functional-type(operands, results)";
 }
 
@@ -1385,8 +1383,6 @@ def Tosa_LogOp : Tosa_ElementwiseUnaryOp<"log"> {
     Extension<[Tosa_EXT_BF16]>,
   ];
 
-  let hasFolder = 1;
-
   let assemblyFormat = "operands attr-dict `:` functional-type(operands, results)";
 }
 

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

@@ -1562,26 +1562,6 @@ OpFoldResult TransposeOp::fold(FoldAdaptor adaptor) {
   return getInput1();
 }
 
-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 {};
-}
-
 OpFoldResult tosa::NegateOp::fold(FoldAdaptor adaptor) {
   // Element-wise negate(negate(x)) = x
   // iff all zero points are constant 0

mlir/test/Dialect/Tosa/canonicalize.mlir

@@ -1104,26 +1104,6 @@ func.func @canonicalize_pad_slice_dynamic_noupdate(%arg0: tensor<1x16x?x3xf32>)
 
 // -----
 
-// CHECK-LABEL: @fold_log_exp
-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>
-}
-
-// -----
-
 // CHECK-LABEL: @fold_negate_negate
 func.func @fold_negate_negate(%arg0: tensor<?x1xf32>) -> tensor<?x1xf32> {
   // CHECK: return %arg{{.*}} : tensor<?x1xf32>