[PATCH] D64512: [InstCombine] Dropping redundant masking before left-shift [0/5] (PR42563)

Thu Jul 18 15:20:55 PDT 2019

lebedev.ri marked 3 inline comments as done.
lebedev.ri added a comment.

@xbolva00, @spatel, @efriedma thank you for the review!

In D64512#1592416 <https://reviews.llvm.org/D64512#1592416>, @efriedma wrote:

> I As discussed at http://lists.llvm.org/pipermail/llvm-dev/2017-March/111257.html, instcombine is probably doing too much work in general given the number of times it's run.

Yep, i agree. Compile time **is** important.

In D64512#1592416 <https://reviews.llvm.org/D64512#1592416>, @efriedma wrote:

> But I don't think this specific use of instsimplify here is likely to be a problem in practice; given the pattern guard, it should trigger very rarely.

Okay then, thank you for taking a look!
I will then proceed with this design (keeping it in instcombine).

Will rebase this addressing inline notes and land this set - the followup patches are
trivial extensions that simply teach it about more similar patterns,
if anyone wants to review those - be my guest, but i'm not expecting any surprises there.

Repository:
  rG LLVM Github Monorepo

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https://reviews.llvm.org/D64512