[Mesa-dev] [RFC 0/9] Add precise/invariant semantics to TGSI

[Nicolai Hähnle]

On 11.06.2017 20:42, Karol Herbst wrote:
> Running Tomb Raider on Nouveau I found some flicker caused by ignoring precise
> modifiers on variables inside Nouveau.
 >
> This series add precise/invariant handling to TGSI, which can be then used by
> drivers to disable certain unsafe optimisations which may otherwise alter
> calculations, which depend on having the same result across shaders.

It's kind of amazing that we got this far without doing this. On the 
radeonsi side, it's probably related to how conservative LLVM is.

But this series is a good idea, since it might allow us to become more 
aggressive with optimizations in radeonsi as well.


> This series fixes this bug in Tomb Raider and one CTS test for 4.4 and 4.5
> 
> Note on Patch 3: I really dislike how I tell glsl_to_tgsi_visitor to apply the
> precise flag on instruction emited in ir_assignment->rhs->accept(); but I found
> no other easy way to handle this. Maybe somebody of you has a better idea?

Sent a suggestion, as well as comments on patches 4 & 5. Patches 1 & 2:

Reviewed-by: Nicolai Hähnle <nicolai.haehnle at amd.com>


> 
> Karol Herbst (9):
>    tgsi: add precise flag to tgsi_instruction
>    tgsi/dump: print _PRECISE modifier on Instrutions
>    st/glsl_to_tgsi: handle precise modifier
>    tgsi: populate precise
>    tgsi/text: parse _PRECISE modifier
>    nv50/ir: add precise field to Instruction
>    nv50/ir/tgsi: handle precise for most ALU instructions
>    nv50/ir: disable mul+add to mad for precise instructions
>    nv50/ir/tgsi: split mad to mul+add
> 
>   src/gallium/auxiliary/tgsi/tgsi_build.c            |  4 +
>   src/gallium/auxiliary/tgsi/tgsi_dump.c             |  4 +
>   src/gallium/auxiliary/tgsi/tgsi_text.c             | 15 +++-
>   src/gallium/auxiliary/tgsi/tgsi_ureg.c             | 14 +++-
>   src/gallium/auxiliary/tgsi/tgsi_ureg.h             | 20 ++++-
>   src/gallium/auxiliary/util/u_simple_shaders.c      |  2 +-
>   src/gallium/drivers/nouveau/codegen/nv50_ir.h      |  1 +
>   .../drivers/nouveau/codegen/nv50_ir_from_tgsi.cpp  | 16 ++++
>   .../drivers/nouveau/codegen/nv50_ir_peephole.cpp   |  6 +-
>   src/gallium/include/pipe/p_shader_tokens.h         |  3 +-
>   src/gallium/state_trackers/nine/nine_shader.c      |  6 +-
>   src/mesa/state_tracker/st_atifs_to_tgsi.c          | 38 ++++-----
>   src/mesa/state_tracker/st_glsl_to_tgsi.cpp         | 92 +++++++++++++++++-----
>   src/mesa/state_tracker/st_mesa_to_tgsi.c           |  8 +-
>   src/mesa/state_tracker/st_pbo.c                    |  2 +-
>   15 files changed, 172 insertions(+), 59 deletions(-)
> 


-- 
Lerne, wie die Welt wirklich ist,
Aber vergiss niemals, wie sie sein sollte.