[PATCH] [InstCombine] Fold endian-independent load sequence into a single load.

[Hal Finkel]

----- Original Message -----
> From: "Michael Spencer" <bigcheesegs at gmail.com>
> To: "Hal Finkel" <hfinkel at anl.gov>
> Cc: "Chandler Carruth" <chandlerc at google.com>, "amara emerson" <amara.emerson at arm.com>, "llvm-commits"
> <llvm-commits at cs.uiuc.edu>, "ahmed bougacha" <ahmed.bougacha at gmail.com>, "david majnemer"
> <david.majnemer at gmail.com>, reviews+D5898+public+a9255b02ad589d6d at reviews.llvm.org
> Sent: Thursday, October 23, 2014 3:00:46 PM
> Subject: Re: [PATCH] [InstCombine] Fold endian-independent load sequence into a single load.
> 
> On Thu, Oct 23, 2014 at 11:48 AM, Hal Finkel <hfinkel at anl.gov> wrote:
> > Chandler, Michael, before we go farther, could you please comment
> > on whether this is an optimal place for this optimization? We do
> > have a LoadCombine pass, maybe it should really go there?
> >
> > Ahmed, I think we also need to check for other uses of the loads...
> > if they also have other uses, then we likely don't want to
> > double-load the same data.
> >
> >  -Hal
> 
> The load combiner was made to deal with this case, however it's not
> enabled right now because load slicing still needs to be implemented
> to deal with some of the performance regressions.

Why would this transformation not cause similar regressions?

 -Hal

> 
> Right now it's in the proper place. The issue is that when we do
> enable load combining, this will be redundant.
> 
> - Michael Spencer
> 
> >
> > ----- Original Message -----
> >> From: "Ahmed Bougacha" <ahmed.bougacha at gmail.com>
> >> To: "ahmed bougacha" <ahmed.bougacha at gmail.com>, "david majnemer"
> >> <david.majnemer at gmail.com>, hfinkel at anl.gov
> >> Cc: "amara emerson" <amara.emerson at arm.com>,
> >> llvm-commits at cs.uiuc.edu
> >> Sent: Wednesday, October 22, 2014 1:58:47 PM
> >> Subject: Re: [PATCH] [InstCombine] Fold endian-independent load
> >> sequence into a single load.
> >>
> >> Keep the alignment from the first byte load instruction.
> >> Also, refactor the ByteLoads handling to make it
> >> endian-independent
> >> (from a memory standpoint).
> >>
> >> The previous patch relied on the later InstCombines to set the
> >> alignment, but we can also do it here. I didn't do that from the
> >> beginning because I couldn't think of a case where that's possible
> >> but the later InstCombine isn't. I still can't, but that's no
> >> reason
> >> not to do it here!
> >>
> >> http://reviews.llvm.org/D5898
> >>
> >> Files:
> >>   lib/Transforms/InstCombine/InstCombine.h
> >>   lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
> >>   test/Transforms/InstCombine/endian-independent-load-BE.ll
> >>   test/Transforms/InstCombine/endian-independent-load-LE-aliasing.ll
> >>   test/Transforms/InstCombine/endian-independent-load-LE.ll
> >>
> >
> > --
> > Hal Finkel
> > Assistant Computational Scientist
> > Leadership Computing Facility
> > Argonne National Laboratory
> 

-- 
Hal Finkel
Assistant Computational Scientist
Leadership Computing Facility
Argonne National Laboratory