[PATCH] D38374: [memcpyopt] Memcpy-memcpy dependence isn't detected across basic blocks

[Daniel Berlin via Phabricator via llvm-commits]

dberlin added a comment.

In https://reviews.llvm.org/D38374#883874, @sunfish wrote:

> In https://reviews.llvm.org/D38374#883738, @dberlin wrote:
>
> > 1. non-local calls in GVN are the cause of pretty much all of it's massive slowdown.
> >
> >   Have you measured the effect this has on larger memory-using testcases?
>
>
> I've measured compile times on some C++ and Rust testcases, and it doesn't appear to significantly slow down -O2. memcpyopt remains under 1% of the time, according to -time-passes.


I'm not opposed if we are willing to revert it.

>> 2. If you are interested, someone already ported it to memoryssa: https://reviews.llvm.org/D26739
> 
> That's interesting, though I'm still interested in the focused and incremental patch here.

Okay. You said"It might be desirable to use MemorySSA, however MemCpyOpt is currently using MemoryDependenceAnalysis for everything, and it seems desirable to avoid using a mix of both within the same pass, and updating the whole pass to use MemorySSA is a bigger project than I'm hoping to take on here."

1. There's now a way to do that, with pretty much no work.
2. Chandler specifically requested that passes be mixed with an option to turn it on off.

So ....


Repository:
  rL LLVM

https://reviews.llvm.org/D38374