3d8fea0e09
There are two problems.
1. This is not NaN safe. 'add.le.sat dst F, Inf F, -Inf F' has a
different result than 'add dst F, Inf F, -Inf F; cmp.le null, dst F, 0F'.
2. Ignoring the first problem, this only produces the desired flags
for LE and G. All other cases can produce the wrong result.
For example, batman_arkham_city_goty.foz 6a63c4caacaa0dae has the
following code:
mad.ge.f0.0(8) g51<1>F g50<8,8,1>F g46<8,8,1>F g11<1,1,1>F
mov.sat(8) g52<1>F g51<1,1,0>F
...
(+f0.0) sel(8) g54<1>UD g53<8,8,1>UD 0x3f000000UD
Without this commit, the saturate is incorrectly propagated to the MAD.
A similar case exists in witcher_3_dxvk_g2.foz 5b03243be667a275.
There are even worse cases like total_war_warhammer3.dx12vk-g6.foz
78328466761ef7ab and ee920491573860fc. The former has the following
code (and the latter has very similar code):
mad.l.f0.0(16) g95<1>F g93<8,8,1>F g62<8,8,1>F g68<1,1,1>F
...
mov.sat(16) g109<1>F -g95<1,1,0>F
...
(+f0.0) sel(16) g68<1>UD g111<1,1,0>UD g54<1,1,0>UD
(+f0.0) sel(16) g70<1>UD g113<1,1,0>UD g56<1,1,0>UD
(+f0.0) sel(16) g72<1>UD g115<1,1,0>UD g58<1,1,0>UD
Saturate propagation makes a hash of this code:
mad.sat.l.f0.0(16) g106<1>F -g93<8,8,1>F -g62<8,8,1>F g68<1,1,1>F
...
(+f0.0) sel(16) g70<1>UD g110<1,1,0>UD g56<1,1,0>UD
(+f0.0) sel(16) g72<1>UD g112<1,1,0>UD g58<1,1,0>UD
(+f0.0) sel(16) g68<1>UD g108<1,1,0>UD g54<1,1,0>UD
Not only is the saturate incorrectly applied to the MAD, but the MAD
result is negated without changing the conditional modifier to G!
NOTE: Backports of this commit to stable branches may need to be more
like the following commit to elk.
shader-db:
All Intel platforms had similar results. (Meteor Lake shown)
total instructions in shared programs: 19729375 -> 19729377 (<.01%)
instructions in affected programs: 112 -> 114 (1.79%)
helped: 0
HURT: 2
total cycles in shared programs: 916234266 -> 916234288 (<.01%)
cycles in affected programs: 636 -> 658 (3.46%)
helped: 0
HURT: 2
fossil-db:
All Intel platforms had similar results. (Meteor Lake shown)
Totals:
Instrs: 151531594 -> 151531601 (+0.00%)
Cycle count: 17209107419 -> 17209107474 (+0.00%); split: -0.00%, +0.00%
Totals from 6 (0.00% of 630198) affected shaders:
Instrs: 4550 -> 4557 (+0.15%)
Cycle count: 194629 -> 194684 (+0.03%); split: -0.00%, +0.03%
Fixes: 947c828d5c ("i965/fs: Add a saturation propagation optimization pass.")
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/29774>
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