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

Fri Mar 5 10:25:06 PST 2021

On 3/4/21 3:05 PM, Artem Belevich wrote:
> 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'.

+1


> --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
>>>>
>