[Mesa-dev] Issue with 3008161d28: st_glsl_to_tgsi: rewrite rename registers to use array fully.

[Dave Airlie]

On 28 July 2017 at 09:37, Brian Paul <brianp at vmware.com> wrote:
> Hi Dave,
>
> We found an issue with this change:
>
> commit 3008161d28e38336ba39aba4769a2deaf9732f55
> Author: Dave Airlie <airlied at redhat.com>
> Date:   Tue May 30 15:52:13 2017 +1000
>
>     st_glsl_to_tgsi: rewrite rename registers to use array fully.
>
>     Instead of having to search the whole array, just use the whole
>     thing and store a valid bit in there with the rename.
>
>     Removes this from the profile on some of the fp64 tests
>
>     Reviewed-by: Timothy Arceri <tarceri at itsqueeze.com>
>     Signed-off-by: Dave Airlie <airlied at redhat.com>
>
> After this patch landed, the number of temporary registers used by the TGSI
> code increased.  With a particular Photoshop shader, the number increased
> from 26 to 31.  With our legacy virtual GPU version, this causes us to run
> out of registers and fail translation.

>
> Did you expect this change to increase the number of temps used?  Is it
> possible to get the old behavior back?  I don't think we can just revert
> this patch since a number of changes since then build on it.

This shouldn't have caused any increase in the number of registers used at all,
it should have just improved the memory usage pattern.

We could probably revert it, I don't think that much changed, it
reverts cleanly,
but I'd really like an apitrace or piglit that shows the problem so I
can work out how where it goes wrong.

Dave.