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

[Michael Spencer]

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.

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