On 2/17/22 18:24, Tobias Burnus wrote:
> PTX version (-mptx=)
> [patch adds -mptx=6.0 as option]
> 
> * Currently supported internally are 3.1 (CUDA 5.0, used by GCC <= 11),
>    6.0 (CUDA 9.0, current GCC 12 default), 6.3 (CUDA 10.0), 7.0 (CUDA 11.0)
> * -mptx= supports 3.1, 6.3, 7.0 – but not the internal default 6.0
> 

I tend not to think in terms of CUDA versions, but supported driver 
versions.

In the end, drivers are used to translate ptx to SASS for execution, 
CUDA is just used for build time verification (or not, if it's not in 
the path).

And a driver may or may not be supported.  F.i. 390.x still may receive 
updates from nvidia, but there are JIT bugs that we've reported that 
they've decided not to fix, so from that point of view 390.x is unsupported.

> I think it makes sense to expose the 6.0 value to the user and not
> only use it internally behind the scenes. As it is already used internally,
> the change is tiny but user visible. 

Sure, I've committed this (with a somewhat shorter commit log).

>Thus, it has to stay when we will
> bump the default in later GCC versions; on the other hand, if we bump
> the default, it might be also a good reason to have it to permit the
> user to have a backward compatible PTX output for linking libraries.
> 

FWIW, I think that it's possible to link different versions of ptx isa 
together (though perhaps there are specific scenarios where that's not 
possible, I'm not sure).  But mixing versions restricts the range of 
drivers you can use, so it may make sense to just use one version.

Thanks,
- Tom