[PATCH] D111806: [LICM] Check the number of divergent paths from loop header to target block

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modimo added subscribers: wenlei, modimo.
modimo added a comment.

To keep the conversation coherent I'll talk about the same feedback for D87551 <https://reviews.llvm.org/D87551> here:

In D111806#3067256 <https://reviews.llvm.org/D111806#3067256>, @reames wrote:

> If we were being presented with hard cases to undo with a cost based transform, I might be willing to entertain the notion that LICM should be non-canonical.  As it stands, I don't see such examples.

The original change that prompted adding this from @wenlei is a more complicated situation https://reviews.llvm.org/D65060#1596899. Specifically, once the values are hoisted out of the 200 switch arms there's not longer a dominating use block to sink them back into. In addition, the block frequency information at that point no longer indicates that there's an issue from the hoisting. Getting MachineLICM to handle that case is complicated and I suspect fragile.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D111806/new/

https://reviews.llvm.org/D111806