[LLVMdev] [PTX] Should we keep backward-compatibility of PTX?

[Justin Holewinski]

On Wed, Mar 9, 2011 at 10:03 PM, Che-Liang Chiou <clchiou at gmail.com> wrote:

> Hi Justin,
>
> There are some backward incompatible features of PTX; for example,
> special registers are redefined as v4i32 (they were v4i16) in PTX 2.0.
> And CUDA 4.0 was rolled out last week. I heard that some instructions
> are deprecated.
>

I have not checked out CUDA 4.0 yet, but any deprecated instructions would
need to be made so as part of a separate PTX version, either 2.2 or 3.0.

My suggestion is to stay thorough with the intrinsics.  Lets create i16 and
i32 versions of both, and emit appropriate cvt instructions if necessary for
the target PTX version.  This should be easy enough using the existing
PTXVersion field in PTXSubtarget.


>
> I am not sure how stable (or unstable) PTX specification is. Do you
> have a rough assessment of its stability?
>

>From what I can tell, it is fairly stable.  When things change, they seem to
primarily be additions to the ISA.


>
> If PTX specification is still fast evolving, I would suggest we keep
> up with latest specification, and consider backward compatibility
> later when it is stabilized. What do you think?
>

I'm fine with that, as long as later PTX versions do not require later
shader models.  I want to maintain compatibility as far back as shader model
1.0 for some older hardware I want to test with.  Besides, I think most of
the functionality in newer PTX versions can be easily predicated with
sub-target flags.


>
> Regards,
> Che-Liang
>



-- 

Thanks,

Justin Holewinski
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