[Mlir-commits] [mlir] [mlir][tensor] Fix PadOp::getConstantPaddingValue (PR #121205)

[Longsheng Mou]

CoTinker wrote:

> Makes sense, thanks. I've left a couple of minor comments.
> 
> Side comment - the test that's been added could quite easily be lowered to `linalg.fill`. Unless I am missing sth? If that's the case, lets leave a TODO somewhere. Probably near the test.

Actually, the constant value inside the PadOp can canonicalize to the outside, such as:
```
// mlir-opt --canonicalize
func.func @generalize_pad_tensor_constant_inside(%arg0: tensor<1x28x28x1xf32>) -> tensor<1x32x32x1xf32> {
  %0 = tensor.pad %arg0 low[0, 2, 2, 0] high[0, 2, 2, 0]  {
  ^bb0(%arg1: index, %arg2: index, %arg3: index, %arg4: index):
    %cst = arith.constant 0.000000e+00 : f32
    tensor.yield %cst : f32
  } : tensor<1x28x28x1xf32> to tensor<1x32x32x1xf32>
  return %0 : tensor<1x32x32x1xf32>
}

--->

func.func @generalize_pad_tensor_constant_inside(%arg0: tensor<1x28x28x1xf32>) -> tensor<1x32x32x1xf32> {
    %cst = arith.constant 0.000000e+00 : f32
    %padded = tensor.pad %arg0 low[0, 2, 2, 0] high[0, 2, 2, 0] {
    ^bb0(%arg1: index, %arg2: index, %arg3: index, %arg4: index):
      tensor.yield %cst : f32
    } : tensor<1x28x28x1xf32> to tensor<1x32x32x1xf32>
    return %padded : tensor<1x32x32x1xf32>
  }
```

https://github.com/llvm/llvm-project/pull/121205