> -----Original Message-----
> From: Gcc-patches <[email protected]> On Behalf Of Kyrylo
> Tkachov
> Sent: 30 April 2020 11:57
> To: Andrew Pinski <[email protected]>; Florian Weimer
> <[email protected]>
> Cc: [email protected]; [email protected]
> Subject: RE: Should ARMv8-A generic tuning default to -moutline-atomics
>
> [Moving to gcc-patches]
>
> > -----Original Message-----
> > From: Gcc <[email protected]> On Behalf Of Andrew Pinski via Gcc
> > Sent: 30 April 2020 07:21
> > To: Florian Weimer <[email protected]>
> > Cc: GCC Mailing List <[email protected]>; [email protected]
> > Subject: Re: Should ARMv8-A generic tuning default to -moutline-atomics
> >
> > On Wed, Apr 29, 2020 at 6:25 AM Florian Weimer via Gcc <[email protected]>
> > wrote:
> > >
> > > Distributions are receiving requests to build things with
> > > -moutline-atomics:
> > >
> > > <https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=956418>
> > >
> > > Should this be reflected in the GCC upstream defaults for ARMv8-A
> > > generic tuning? It does not make much sense to me if every distribution
> > > has to overide these flags, either in their build system or by patching
> > > GCC.
> >
> > At least we should make it a configure option.
> > I do want the ability to default it for our (Marvell) toolchain for
> > Linux (our bare metal toolchain will be defaulting to ARMv8.2-a
> > anyways).
>
> After some internal discussions, I am open to having it on as a default.
> Here are two versions. One has it as a tuning setting that CPUs can override,
> the other just switches it on by default always unless overridden by -mno-
> outline-atomics.
> I slightly prefer the second one as it's cleaner and simpler, but happy to
> take
> either.
> Any preferences?
> Thanks,
> Kyrill
>
> ChangeLogs:
>
> 2020-04-30 Kyrylo Tkachov <[email protected]>
>
> * config/aarch64/aarch64-tuning-flags.def (no_outline_atomics):
> Declare.
> * config/aarch64/aarch64.h (TARGET_OUTLINE_ATOMICS): Define.
> * config/aarch64/aarch64.opt (moutline-atomics): Change to Int
> variable.
>
> 2020-04-30 Kyrylo Tkachov <[email protected]>
>
> * config/aarch64/aarch64.h (TARGET_OUTLINE_ATOMICS): Define.
> * config/aarch64/aarch64.opt (moutline-atomics): Change to Int
> variable.
> * doc/invoke.texi (moutline-atomics): Document as on by default.
>
I've pushed this second variant after bootstrap and testing on
aarch64-none-linux-gnu.
Compiled a simple atomic-using testcase with all relevant combinations of
-moutline-atomics and LSE and no-LSE -march options.
Before the results were (as expected):
|-moutline-atomics | -mno-outline-atomics | <no outline-atomics option
--------------------------------------------------------------------------------
LSE | inline LSE | inline LSE | inline LSE
no-LSE | outline | inline LDXR/STXR | inline LDX/STXR
with this patch they are:
-moutline-atomics | -mno-outline-atomics | <no outline-atomics option>
--------------------------------------------------------------------------------
LSE | inline LSE | inline LSE | inline LSE
no-LSE | outline | inline LDXR/STXR | outline
Thanks,
Kyrill
