In reality, a lot of users are still using old gcc versions running on new hardware. OpenJDK is a typical example, I think.
> -----Original Message----- > From: Richard Earnshaw <richard.earns...@foss.arm.com> > Sent: Friday, May 1, 2020 6:41 PM > To: JiangNing OS <jiangn...@os.amperecomputing.com>; Kyrylo Tkachov > <kyrylo.tkac...@arm.com>; Andrew Pinski <pins...@gmail.com>; Florian > Weimer <fwei...@redhat.com> > Cc: gcc-patches@gcc.gnu.org; nmeye...@amzn.com > Subject: Re: Should ARMv8-A generic tuning default to -moutline-atomics > > On 01/05/2020 11:38, JiangNing OS via Gcc-patches wrote: > > Hi Kyrill, > > > > Can it be backported to gcc 8/9/10 branches? > > > > I'm not sure changing the defaults of things like this is a good idea on 'dot' > releases. > > Having the option is one thing. Changing the default another thing entirely. > > R. > > > Thanks, > > -Jiangning > > > >> -----Original Message----- > >> From: Gcc-patches <gcc-patches-boun...@gcc.gnu.org> On Behalf Of > >> Kyrylo Tkachov > >> Sent: Thursday, April 30, 2020 8:27 PM > >> To: Kyrylo Tkachov <kyrylo.tkac...@arm.com>; Andrew Pinski > >> <pins...@gmail.com>; Florian Weimer <fwei...@redhat.com> > >> Cc: gcc-patches@gcc.gnu.org; nmeye...@amzn.com > >> Subject: RE: Should ARMv8-A generic tuning default to > >> -moutline-atomics > >> > >> > >> > >>> -----Original Message----- > >>> From: Gcc-patches <gcc-patches-boun...@gcc.gnu.org> On Behalf Of > >>> Kyrylo Tkachov > >>> Sent: 30 April 2020 11:57 > >>> To: Andrew Pinski <pins...@gmail.com>; Florian Weimer > >>> <fwei...@redhat.com> > >>> Cc: gcc-patches@gcc.gnu.org; nmeye...@amzn.com > >>> Subject: RE: Should ARMv8-A generic tuning default to > >>> -moutline-atomics > >>> > >>> [Moving to gcc-patches] > >>> > >>>> -----Original Message----- > >>>> From: Gcc <gcc-boun...@gcc.gnu.org> On Behalf Of Andrew Pinski via > >>>> Gcc > >>>> Sent: 30 April 2020 07:21 > >>>> To: Florian Weimer <fwei...@redhat.com> > >>>> Cc: GCC Mailing List <g...@gcc.gnu.org>; nmeye...@amzn.com > >>>> Subject: Re: Should ARMv8-A generic tuning default to > >>>> -moutline-atomics > >>>> > >>>> On Wed, Apr 29, 2020 at 6:25 AM Florian Weimer via Gcc > >>>> <g...@gcc.gnu.org> > >>>> 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 <kyrylo.tkac...@arm.com> > >>> > >>> * 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 <kyrylo.tkac...@arm.com> > >>> > >>> * 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
