[Mesa-dev] [RFC PATCH 1/2] r600/sb: Set flags for GROUP_BARRIER instruction and force it into slot X

[Gert Wollny]

Am Mittwoch, den 10.01.2018, 16:36 +0100 schrieb Gert Wollny:
> This seems to satisfy the sb optimizer, i.e. no regressions in the
> piglits compared to disabling sb for tesselation shaders with
> barriers but enabling them in general.
> ---

Actually, it seems this is not enough, at least for Tomb Raider which
uses one tessellation control shader with a barrier. The optimizer
reorders the LDS instructions around the barrier in a way that in the
optimized version there are more reads before it than in the original
byte code. 

The number of writes is the same though, and as far as I can tell from
the TGSI, the values written to LDS before the barrier are not read
back within the shader - which makes me wonder whether the barrier is
actually necessary.

Best,
Gert