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

[Diana Picus via llvm-dev]

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
* Improving constant placement: http://bugs.llvm.org/show_bug.cgi?id=32561
* 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


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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