[llvm] r257875 - [InstCombine] Rewrite bswap/bitreverse handling completely.

[David Majnemer via llvm-commits]

Yes.

On Tue, Jan 19, 2016 at 9:33 AM, Hans Wennborg <hans at chromium.org> wrote:

> This should have baked on the buildbots for a while now.
>
> David, OK to merge?
>
> On Fri, Jan 15, 2016 at 10:25 AM, James Molloy <James.Molloy at arm.com>
> wrote:
> > Hi Hans,
> >
> > Yes, as long as David is happy please merge this, along with the
> followup that fixes msan.
> >
> > I was waiting for it to soak through the stage2 bots before suggesting
> it myself.
> >
> > James
> >
> >
> >
> >> On 15 Jan 2016, at 17:59, Hans Wennborg <hans at chromium.org> wrote:
> >>
> >> It was suggested that this be merged to 3.8. David, I think you're the
> >> code owner here; OK for merge?
> >>
> >> On Fri, Jan 15, 2016 at 1:20 AM, James Molloy via llvm-commits
> >> <llvm-commits at lists.llvm.org> wrote:
> >>> Author: jamesm
> >>> Date: Fri Jan 15 03:20:19 2016
> >>> New Revision: 257875
> >>>
> >>> URL: http://llvm.org/viewvc/llvm-project?rev=257875&view=rev
> >>> Log:
> >>> [InstCombine] Rewrite bswap/bitreverse handling completely.
> >>>
> >>> There are several requirements that ended up with this design;
> >>>  1. Matching bitreversals is too heavyweight for InstCombine and
> doesn't really need to be done so early.
> >>>  2. Bitreversals and byteswaps are very related in their matching
> logic.
> >>>  3. We want to implement support for matching more advanced
> bswap/bitreverse patterns like partial bswaps/bitreverses.
> >>>  4. Bswaps are best matched early in InstCombine.
> >>>
> >>> The result of these is that a new utility function is created in
> Transforms/Utils/Local.h that can be configured to search for bswaps,
> bitreverses or both. InstCombine uses it to find only bswaps, CGP uses it
> to find only bitreversals.
> >>>
> >>> We can then extend the matching logic in one place only.
> >>
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