[cfe-dev] [RFC] Unified offloading option for CUDA/HIP/OpenMP

[Artem Belevich via cfe-dev]

On Thu, Mar 4, 2021 at 10:34 AM Liu, Yaxun (Sam) <Yaxun.Liu at amd.com> wrote:

> [AMD Public Use]
>
> There is another aspect we need to consider: how to modify the -target
> option by additional options?
>
> For the existing --offload-arch option, we could use -Xarch_ to add
> specific options for it.
>

`-Xarch_xxx` as implemented right now is a rather limiter hack. IIRC it
only accepts options w/o arguments which limits its usability.


> Assuming we have an -offload="amdgcn -mcpu=gfx906" option, then we want
> to add some options specific to it by an additional option, what should we
> do?
>

I think we've been conflating telling the driver what to compile for and
customizing individual sub-compilations.

We could explicitly separate the two tasks. E.g.:
`--[no-]offload=target1,target2,target3...`
`--Xoffload=target_pattern target_options...`

This way your example would be handled with:
"--offload=gfx906,gfx1010"
"--Xoffload=gfx* options common to all AMD GPUs"
"--Xoffload=gfx906 -mcpu=gfx906 --fsomething-specific-to-gfx906"

In the end `-Xarch_xxx` would become an alias for '-Xoffload=xxx'.

--Artem




>
> Thanks.
>
> Sam
>
> -----Original Message-----
> From: Doerfert, Johannes <jdoerfert at anl.gov>
> Sent: Thursday, February 11, 2021 12:59 PM
> To: Artem Belevich <tra at google.com>; Liu, Yaxun (Sam) <Yaxun.Liu at amd.com>
> Cc: Ben Boeckel <ben.boeckel at kitware.com>; Lieberman, Ron <
> Ron.Lieberman at amd.com>; a.bataev at hotmail.com; Chan, SiuChi <
> siuchi.chan at amd.com>; Searles, Mark <Mark.Searles at amd.com>; cfe-dev (
> cfe-dev at lists.llvm.org) <cfe-dev at lists.llvm.org>; jeffrey.sandoval at hpe.com;
> Jon Chesterfield <jonathanchesterfield at gmail.com>
> Subject: Re: [cfe-dev] [RFC] Unified offloading option for CUDA/HIP/OpenMP
>
> [CAUTION: External Email]
>
> I'm OK with either.
>
> On 2/11/21 11:42 AM, Artem Belevich wrote:
> > On Thu, Feb 11, 2021 at 8:30 AM Liu, Yaxun (Sam) <Yaxun.Liu at amd.com>
> wrote:
> >
> >> [AMD Public Use]
> >>
> >>
> >>
> >> Sorry for the delay.
> >>
> >>
> >>
> >> Both Johannes’ and Artem’s proposals should satisfy the needs of users:
> >>
> >>
> >>
> >> Option 1:
> >>
> >>
> >>
> >> `-offload=<offload-pattern> optA optB optC`.
> >>
> >>
> >>
> >> Option 2:
> >>
> >>
> >>
> >> `-offload=<offload-pattern>,optA,optB,optC`.
> >>
> > I'm fine with #2. We're using something similar with our build tools
> > and it works reasonably well.
> > However, it does have one annoying corner case. There's no easy way to
> > pass an option which has a comma in it. E.g. if I want to pass
> > `-Wl,something,something`. Perhaps we could use sed-like approach and
> > allow changing the separator. E.g. `s/a/b/` == `s at a@b@`.
> >
> > --Artem
> >
> >
> >
> >>
> >> Compared to the old options, they are more concise and more readable.
> >>
> >>
> >>
> >> The main difference is the delimiter. To me option 2 is more
> >> attractive since it does not need quotations for most cases.
> >>
> >>
> >>
> >> Can we reach an agreement on option 2?
> >>
> >>
> >>
> >> Thanks.
> >>
> >>
> >>
> >> Sam
> >>
> >>
> >>
> >>
> >>
> >> *From:* Artem Belevich <tra at google.com>
> >> *Sent:* Tuesday, December 15, 2020 2:13 PM
> >> *To:* Ben Boeckel <ben.boeckel at kitware.com>
> >> *Cc:* Doerfert, Johannes <jdoerfert at anl.gov>; Liu, Yaxun (Sam) <
> >> Yaxun.Liu at amd.com>; Lieberman, Ron <Ron.Lieberman at amd.com>;
> >> a.bataev at hotmail.com; Chan, SiuChi <siuchi.chan at amd.com>; Searles,
> >> Mark < Mark.Searles at amd.com>; cfe-dev (cfe-dev at lists.llvm.org) <
> >> cfe-dev at lists.llvm.org>
> >> *Subject:* Re: [cfe-dev] [RFC] Unified offloading option for
> >> CUDA/HIP/OpenMP
> >>
> >>
> >>
> >> [CAUTION: External Email]
> >>
> >>
> >>
> >>
> >>
> >> On Tue, Dec 15, 2020 at 10:23 AM Ben Boeckel
> >> <ben.boeckel at kitware.com>
> >> wrote:
> >>
> >> On Mon, Dec 14, 2020 at 14:04:43 -0800, Artem Belevich via cfe-dev
> wrote:
> >>> It all may be an utter overkill, too. WDYT?
> >> Note that tools such as ccache and sccache generally need to be able
> >> to understand what's going on (I believe distcc and other distributed
> >> compilation tools also generally need to know too), so making it
> >> sensible enough for interpretation based on just the flags to be
> >> possible should be considered.
> >>
> >>
> >>
> >> I think this is somewhat orthogonal to how we specify per-target
> options.
> >> Such a tool almost never knows about all possible compiler options
> >> and has to pass through the unknown options as-is.  However, any form
> of 'nested'
> >> options specified on the command line will have a chance to confuse
> >> such tool. E.g. if I want to pass '-E' to some sub-tool for a
> >> particular offload-target, ccache, not being aware that it's not a
> >> top-level compilation option, may interpret it as an attempt to
> preprocess the TU.
> >>
> >>
> >>
> >> I wonder if it would make sense to just move all this per-target
> >> option complexity into an external response file. As far as existing
> >> tools are concerned, it would look like
> >> `--offload-options=target-opts.file` without affecting tool's general
> >> idea what this compilation is about to do, and the external file
> >> would allow us to be as flexible as we need to be to specify per-target
> options. It could be just a flat list of pairs `-Xarch_...
> >> optA`.  Or we could use YAML.
> >>
> >>
> >>
> >> That approach, however, has its own issues and would still need to be
> >> optional. If it's the only way to specify offload options, that will
> >> complicate other use cases as now they would have to deal with
> >> temporary files.
> >>
> >>
> >>
> >> Maybe a slightly modified variant of jdoefert@'s idea would work
> better:
> >>
> >>>>>     -offload="amd -march=gfx906 -fno-vectorize" -fopenmp
> >>
> >>
> >> Implement it in a way similar to -Wl,optA,optB,optC and extend it to
> >> match an offload scope glob/regex.
> >>
> >> E.g. `-offload=<offload-pattern>,optA,optB,optC`.
> >>
> >> As far as the external tools are concerned, it's just one option to
> >> pass though. At the same time it should be flexible enough to apply
> >> the options to subset of offload targets in a human-manageable way.
> >>
> >>
> >>
> >> --
> >>
> >> --Artem Belevich
> >>
> >
>


-- 
--Artem Belevich
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