[PATCH] D40480: MemorySSA backed Dead Store Elimination.

[Dave Green via Phabricator via llvm-commits]

dmgreen added a comment.

Thanks for taking a look at this, it would be good to make use of it. You may want to check the llvm-commits mails for more of Daniels thoughts, as they unfortunately didn't make it into phabricator.

IIRC my plan was to add some sort of caching to isOverwrite, to reduce the number of required calls to getUnderlyingObject/whatever else in that function can take time. That helped speed things up in some cases, but still left some times that this wasn't as quick as I would like. It may still be quicker than the "old" pass overall.

There is also a patch somewhere to make LICM preserve PDT's which would mean we get it for free. That's not needed before this though, it just cuts down the time again. From the old tests I did it seemed that this version of dse was quicker, but the analysis we need are not free. I was looking for cross-basic-block DSE, so was happy enough paying the price. I believe you are looking for something that has less degenerate compile time regressions?

> Can you add tests for `volatile`?

The idea here would be that that enable-dse-memoryssa would be set to true eventually, so this should pass every existing DSE test. The old parts of this file could then be deleted. The multiblock tests are new as that's not something the old pass could do. I'm not sure if this will still pass all the existing tests, or if the old DSE algorithm has learnt new tricks since then.


https://reviews.llvm.org/D40480