intel: Fix SIMD16 unaligned payload GRF reads on Gen4-5.
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: 8aee87fe (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> (cherry picked from commit 08a5c395)