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

[Diana Picus via llvm-dev]

Got another one: https://bugs.llvm.org/show_bug.cgi?id=33036

I'm still investigating whether this is an actual GlobalISel issue or
something else (I'll also start a build on a more recent revision to
see how that behaves).

On 12 May 2017 at 20:06, Eric Christopher <echristo at gmail.com> wrote:
> Agreed. That was probably just luck before :)
>
> -eric
>
> On Fri, May 12, 2017 at 5:22 AM Diana Picus via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
>>
>> 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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>> >> llvm-dev at lists.llvm.org
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>> >>
>> >>
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