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

Sat Mar 6 07:13:06 PST 2021

[AMD Public Use]

We need to different target triples since it may not always be possible to infer target triple by cpu name. So I guess it would be like:

"--offload=amdgcn-gfx906,amdgcn-gfx1010"
"--Xoffload=amdgcn-gfx* options common to all AMD GPUs"
"--Xoffload=amdgcn-gfx906 -mcpu=gfx906 --fsomething-specific-to-gfx906"

Sam

-----Original Message-----
From: Doerfert, Johannes <jdoerfert at anl.gov> 
Sent: Friday, March 5, 2021 1:25 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>; Rodgers, Gregory <Gregory.Rodgers at amd.com>
Subject: Re: [cfe-dev] [RFC] Unified offloading option for CUDA/HIP/OpenMP

[CAUTION: External Email]

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
>>>>
>