[Mlir-commits] [mlir] [mlir][Analysis] Remove return value from `getBackwardSlice` (PR #163749)

[Ian Wood]

IanWood1 wrote:

>Why check for `!parentOp->hasTrait<OpTrait::IsIsolatedFromAbove>()`? I read through #158135, but it still does not make sense to me. Why does it matter whether the operation is isolated from above? We're jumping from a region to its parent op in this traversal. (We are not looking at value captures.)

I didn't fully agree with keeping the check for `IsIsolatedFromAbove`. However, block arg handling was a bit out of scope for the change I was trying to make. The check was meant to preserve the current block arg behavior. The most compelling argument was:

> This is based on the `IsolatedFromAbove` initially being a generalization of function-like operations to `gpu.launch`, where one should avoid accessing values outside the region at all cost since they physically live on a different device.

@ftynse might do a better job at explaining.

https://github.com/llvm/llvm-project/pull/163749