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Re: [patch] Add support for #pragma GCC unroll
- From: Bernhard Reutner-Fischer <rep dot dot dot nop at gmail dot com>
- To: Steve Kargl <sgk at troutmask dot apl dot washington dot edu>
- Cc: Eric Botcazou <ebotcazou at adacore dot com>, GCC Patches <gcc-patches at gcc dot gnu dot org>, Richard Biener <richard dot guenther at gmail dot com>, Mike Stump <mikestump at comcast dot net>, gfortran <fortran at gcc dot gnu dot org>
- Date: Mon, 20 Nov 2017 21:21:57 +0100
- Subject: Re: [patch] Add support for #pragma GCC unroll
- Authentication-results: sourceware.org; auth=none
- References: <3136854.5zjt3GTbhu@polaris> <CAFiYyc1rKGUtEc8MEKetP7=sD6GXs9avKGsY3o0tjF-O1hpT1g@mail.gmail.com> <585BCFAB-107C-402E-B17A-CBD0E39419F2@gmail.com> <5042915.qGEuR7vFt9@polaris> <CAC1BbcRh7vLvmLyk-q9ieoPQ7HYLQua5Y3FS0YXhvOPPkyQDfw@mail.gmail.com> <20171120144501.GA2949@troutmask.apl.washington.edu>
On 20 November 2017 at 15:45, Steve Kargl
<sgk@troutmask.apl.washington.edu> wrote:
> On Mon, Nov 20, 2017 at 12:57:47PM +0100, Bernhard Reutner-Fischer wrote:
>> On 20 November 2017 at 12:26, Eric Botcazou <ebotcazou@adacore.com> wrote:
>> >> If anybody finds the time to push the corresponding Fortran changes then I'd
>> >> be grateful. I won't have time for this until end of stage 1...
>> >>
>> >> https://gcc.gnu.org/ml/fortran/2015-02/msg00014.html
>> >
>> > OK, I'm going to merge it in the main patch.
>>
>> [CCing fortran@]
>> Thanks alot in advance!
>
> The URL points to a nearly 3 year old patch. I noticed
> that there is no documentation of the new Fortran directive.
> Section 7.2 of gfortran.info should be updated. In particular,
> does '!GCC$ UNROLL 4' affect only the immediately following
> DO-LOOP or all DO-LOOPs that follow the directive until another
> 'GCC$ UNROLL ...' is found? How does this new directive interface
> with OpenMP and OpenACC?
The documentation for the directive is missing indeed. We can fix this
during stage3.
Currently the directive works on the whole function (see
gfc_cfun_has_unroll()) and instructs the loop-optimizers to run on
that function.
The loop-optimizers will discover the ANNOTATE_EXPR and act accordingly.
Richard B. already noted that the RTL unroller might do more than
intended, see https://gcc.gnu.org/ml/gcc-patches/2017-11/msg01468.html
I expect updates to the C and C++ in this area to be reflected to Fortran too.
The interaction with OpenMP and OpenACC in the Fortran FE is the same
as in the other frontends, obviously.
Eric's current respin of Mikes patch is here, FYI:
https://gcc.gnu.org/ml/gcc-patches/2017-11/msg01452.html
thanks,