[llvm-dev] [GlobalISel][AArch64] Toward flipping the switch for O0: Please give it a try!

[Diana Picus via llvm-dev]

It turns out that can be fixed by adding -lm to the link line, so I
will probably convert it into a test-suite bug.

I don't suppose it's crucial to handle the fabs intrinsic nicely at -O0.

On 12 May 2017 at 13:44, Diana Picus <diana.picus at linaro.org> wrote:
> Hi,
>
> I ran into a little snag on the test-suite:
> https://bugs.llvm.org/show_bug.cgi?id=33021
> It boils down to GlobalISel generating calls to fabs instead of using
> FABSDr (so we get undefined references).
>
> Cheers,
> Diana
>
> On 11 May 2017 at 18:40, Quentin Colombet <qcolombet at apple.com> wrote:
>> Hi Diana,
>>
>> Thanks for the summary.
>>
>> On May 11, 2017, at 4:01 AM, Diana Picus <diana.picus at linaro.org> wrote:
>>
>> Hi all,
>>
>> I'm still running some validation on this, I'll send an email when
>> it's done. If that goes well I don't have anything against making the
>> switch.
>>
>> For the record, here's a summary of issues that were deferred for
>> later on (some of which are optimization-ish and we might decide to
>> never do at -O0 at all):
>> * Crash in RegBankSelect for half fp types:
>> https://bugs.llvm.org/show_bug.cgi?id=32560
>>
>>
>> I’ll have a look.
>>
>> * Improving constant placement: http://bugs.llvm.org/show_bug.cgi?id=32561
>>
>>
>> I’ve commented in the PR to mention the localizer technic I was playing
>> with, if someone wants to give it a try.
>>
>> * Fancy switch lowering
>> * Transforming division-by-constant-power-of-2 into right shift
>>
>>
>> AFAICT all the other issues that were brought up were fixed (yay!).
>>
>> Cheers,
>> Diana
>>
>>
>> Cheers,
>> -Quentin
>>
>>
>>
>> On 11 May 2017 at 08:44, Kristof Beyls via llvm-dev
>> <llvm-dev at lists.llvm.org> wrote:
>>
>>
>> On 10 May 2017, at 17:36, Quentin Colombet <qcolombet at apple.com> wrote:
>>
>>
>> MultiSource/Benchmarks/mediabench/mpeg2/mpeg2dec/mpeg2decode (46%): Function
>> Reference_IDCT: Probably due to creating all constants in the entry BB +
>> spilling floating point data through an X register:
>>
>> FastISel:
>> fadd d0, d1, d0
>> str d0, [sp,#528]
>> GlobalISel:
>> fadd d0, d1, d0
>> fmov x9, d0
>> stur x9, [x29,#-48]
>>
>>
>> Good finding, I forgot to do stores in my previous fix. I’ll do them
>> shortly.
>>
>>
>> Should be fixed by r302679
>>
>>
>> Thanks Quentin,
>>
>> That reduces the slow-down when enabling globalisel at -O0 from 13% (on
>> r302453)  to 9.5% (on r302679) in my experiments.
>> The code size increase also reduces from just over 3% to 2.8%.
>>
>> Kristof
>>
>>
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