[Mesa-dev] soft fp64 support - main body (glsl/gallium)

Dave Airlie airlied at gmail.com
Tue Mar 13 04:24:25 UTC 2018

This is the main code for the soft fp64 work. It's mostly Elie's
code with a bunch of changes by me.

This patchset has all the glsl lowering code. (using float64.glsl,
yes I know checked in files are bad, but not bad enough for anyone
to have solved int64.glsl yet, so we have a precedent).

It introduces the builtin code for all the functions first,
this code has seen some optimisation using findMSB and mix opcodes
to remove if branches, I'm sure it could see a lot more. if statements
are the enemy, esp when you hit glsl copy prop and the r600/sb backend.

The second part is just the lowering hooks to use the builtins,
but also to do a bunch of non-builtin lowering.

Finally the gallium patches adds a new interpreation for the PIPE_CAP_DOUBLES,
allowing drivers to choose if they want no fp64, hw fp64, or emulated fp64.
I don't think we should be enabling this for everyone, just drivers who ask.

There is no r600 patch in this series, it's a one liner, but the code does
cause a lot of long compile times in both the glsl compiler and the r600
backend, however I'd really like to get this stuff checked in so we have
 a known stable good base (it passes
[1375/1375] skip: 5, pass: 1368, fail: 2
on r600 nosb at the moment).

I think most of the remaining issues are not to be found in this code,
but fixes for the other parts of the stack.

Also I'm not really interested in bikeshedding the nitty gritty details
of the fp64 emulation, the main goal for this code is to provide the
fp64 bit so we can enable GL4.3 on evergreen GPUs, I don't think anyone
is going to use it that often in practice, and if we can get it to the
level that passes conformance (still WIP) then I'll be happy. I think
optimising it to reduce CPU usage at compile time is way more important
than optimising it to reduce GPU usage.


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