[Mlir-commits] [flang] [mlir] [mlir][CSE] Introduce hoist-pure-ops logic to CSE pass (PR #180556)

[lonely eagle]

linuxlonelyeagle wrote:

> > This means that although I am hoisting operations here, it does not fundamentally change the relative positioning of blocks within the region. Therefore, DominanceInfo and PostDominanceInfo remain valid.
> 
> Contrary to LLVM, we do have regions: when we CSE an operation with regions it means we're deleting blocks. Are we deleting the entry for these regions in the analysis cache?

In DominanceInfoBase, a DenseMap is used to store the dominator tree for each region. I think we should also remove the stale cache from this map when a region-carrying operation is deleted. We could explicitly add a method to DominanceInfoBase to erase a region's dominator tree; otherwise, the memory occupied by these trees won't be released until DominanceInfo itself is destroyed.

https://github.com/llvm/llvm-project/pull/180556