[PATCH] [SimplifyCFG] Swap to using TargetTransformInfo for cost analysis.

[Andrea Di Biagio]

On Tue, Feb 10, 2015 at 5:13 PM, Andrea Di Biagio
<andrea.dibiagio at gmail.com> wrote:
> On Tue, Feb 10, 2015 at 5:12 PM, Hal Finkel <hfinkel at anl.gov> wrote:
>> ----- Original Message -----
>>> From: "Andrea Di Biagio" <andrea.dibiagio at gmail.com>
>>> To: "Hal Finkel" <hfinkel at anl.gov>
>>> Cc: "James Molloy" <james at jamesmolloy.co.uk>, reviews+D7506+public+d608f0951474be02 at reviews.llvm.org,
>>> "llvm-commits at cs.uiuc.edu for LLVM" <llvm-commits at cs.uiuc.edu>
>>> Sent: Tuesday, February 10, 2015 10:59:15 AM
>>> Subject: Re: [PATCH] [SimplifyCFG] Swap to using TargetTransformInfo for cost analysis.
>>>
>>> Hi James, Hal
>>>
>>> thanks for the feedback.
>>>
>>> In that case, I'll see if I can come up with a fix to improve the
>>> cost
>>> of intrinsic calls for x86.
>>> On x86, the cost of cttz/ctlz would be either TCC_Basic or
>>> TCC_Expensive based on whether we have certain features.
>>>
>>> @Hal: Does it mean that this patch would make the the code I added in
>>> CodeGenPrepare to speculate calls to cttz/ctlz redundant? I see that
>>> with this patch, some of the test cases in CodeGen/X86/lzcnt-tzcnt.ll
>>> are now optimized by SimplifyCFG. The only unoptimized cases are
>>> those
>>> where the 'then' block contains extra instructions. I guess D7507
>>> will
>>> take care of it.
>>>
>>> Please correct me if I am wrong.
>>
>> I think you're right; it should get the simple speculation case. Will it also get the cases where we clear the 'undef on zero' flag?
>>
>>  -Hal
>
> Yes, it would work because of this revision:

Forget my last email...

It will get the 'undef on zero' flag because of revision 227197.
http://llvm.org/viewvc/llvm-project?view=revision&revision=227197

>
>>
>>>
>>> Thanks!
>>> Andrea
>>>
>>> On Tue, Feb 10, 2015 at 4:27 PM, Hal Finkel <hfinkel at anl.gov> wrote:
>>> > ----- Original Message -----
>>> >> From: "James Molloy" <james at jamesmolloy.co.uk>
>>> >> To: reviews+D7506+public+d608f0951474be02 at reviews.llvm.org, "james
>>> >> molloy" <james.molloy at arm.com>, hfinkel at anl.gov,
>>> >> "t p northover" <t.p.northover at gmail.com>, "Andrea DiBiagio"
>>> >> <Andrea_DiBiagio at sn.scee.net>
>>> >> Cc: llvm-commits at cs.uiuc.edu
>>> >> Sent: Tuesday, February 10, 2015 10:22:07 AM
>>> >> Subject: Re: [PATCH] [SimplifyCFG] Swap to using
>>> >> TargetTransformInfo for cost analysis.
>>> >>
>>> >>
>>> >> Hi Andrea,
>>> >>
>>> >> Performance on AArch64 showed no major swings. However, it sounds
>>> >> to
>>> >> me like your TargetTransformInfo isn't behaving correctly. That's
>>> >> TTI's entire point, and the x86 one should surely return
>>> >> "TCC_Expensive" for such intrinsic calls.
>>> >>
>>> >> I see that the default TTI does return TCC_Basic for almost all
>>> >> intrinsics, and that is arguable behaviour. But there's no reason
>>> >> you shouldn't override this. In fact, it seems the right thing to
>>> >> do.
>>> >>
>>> >
>>> > I agree, x86 should override these. I'll add that we're going to
>>> > run into this more because we're starting to use the user-cost
>>> > interface for more things. The target's user-cost implementations
>>> > are not as well tuned as the cost interfaces used by the
>>> > vectorizer.
>>> >
>>> >  -Hal
>>> >
>>> >>
>>> >> Cheers,
>>> >>
>>> >>
>>> >> James
>>> >>
>>> >> On Tue Feb 10 2015 at 2:53:52 PM Andrea Di Biagio <
>>> >> Andrea_DiBiagio at sn.scee.net > wrote:
>>> >>
>>> >>
>>> >> REPOSITORY
>>> >> rL LLVM
>>> >>
>>> >> http://reviews.llvm.org/D7506
>>> >>
>>> >> EMAIL PREFERENCES
>>> >> http://reviews.llvm.org/ settings/panel/ emailpreferences/
>>> >>
>>> >>
>>> >>
>>> >> ______________________________ _________________
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>>> >>
>>> >
>>> > --
>>> > Hal Finkel
>>> > Assistant Computational Scientist
>>> > Leadership Computing Facility
>>> > Argonne National Laboratory
>>> > _______________________________________________
>>> > llvm-commits mailing list
>>> > llvm-commits at cs.uiuc.edu
>>> > http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
>>>
>>
>> --
>> Hal Finkel
>> Assistant Computational Scientist
>> Leadership Computing Facility
>> Argonne National Laboratory