[PATCH] D82618: [MemorySSA] Update comment in PassBuilder

[Yuanfang Chen via Phabricator via llvm-commits]

ychen added a comment.

In D82618#2116101 <https://reviews.llvm.org/D82618#2116101>, @asbirlea wrote:

> It's not impossible. It's hard and likely not worth it.
>  Preserving MemorySSA for this pass means creating MemoryAccesses for all blocks cloned when unrolling. Creating an access and then updating so many times is likely more expensive than recomputing MemorySSA from scratch.
>
> I have a patch lined up where MemorySSA would be set to true when unroll added to LPM2, but preliminary testing didn't show this case to provide much value.


Thanks for the information @asbirlea . It is very helpful.


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https://reviews.llvm.org/D82618