Kenneth Graunke
08a5c395ab
When the SIMD16 Gen4-5 fragment shader payload contains source depth
(g2-3), destination stencil (g4), and destination depth (g5-6), the
single register of stencil makes the destination depth unaligned.
We were generating this instruction in the RT write payload setup:
mov(16) m14<1>F g5<8,8,1>F { align1 compr };
which is illegal, instructions with a source region spanning more than
one register need to be aligned to even registers. This is because the
hardware implicitly does (nr | 1) instead of (nr + 1) when splitting the
compressed instruction into two mov(8)'s.
I believe this would cause the hardware to load g5 twice, replicating
subspan 0-1's destination depth to subspan 2-3. This showed up as 2x2
artifact blocks in both TIS-100 and Reicast.
Normally, we rely on the register allocator to even-align our virtual
GRFs. But we don't control the payload, so we need to lower SIMD widths
to make it work. To fix this, we teach lower_simd_width about the
restriction, and then call it again after lower_load_payload (which is
what generates the offending MOV).
Fixes: 8aee87fe4c (i965: Use SIMD16 instead of SIMD8 on Gen4 when possible.)
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107212
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=13728
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Tested-by: Diego Viola <diego.viola@gmail.com>
`Mesa <https://mesa3d.org>`_ - The 3D Graphics Library
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