i965/vec4: Fix saturation errors when coalescing registers
If the register types do not match and the instruction
that contains the final destination is saturated, register
coalescing generated non-equivalent code.
This did not happen when using IR because types usually
matched, but it is visible in nir-vec4.
For example,
mov vgrf7:D vgrf2:D
mov.sat m4:F vgrf7:F
is coalesced to:
mov.sat m4:D vgrf2:D
The patch prevents coalescing in such scenario, unless the
instruction we want to coalesce into is a MOV (without type
conversion implied). In that case, the patch sets the register
types to the type of the final destination.
Shader-db results in HSW (only vec4 instructions shown):
total instructions in shared programs: 1754415 -> 1754416 (0.00%)
instructions in affected programs: 74 -> 75 (1.35%)
helped: 0
HURT: 1
GAINED: 0
LOST: 0
Only one extra instruction in one of the shaders, that comes from
eliminating a saturation error by preventing register coalesce.
Cc: "10.6 11.0" <mesa-stable@lists.freedesktop.org>
Reviewed-by: Jason Ekstrand <jason.ekstrand@intel.com>
1 file changed