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From the Kaby Lake PRM Vol. 7 "Assigning Conditional Flags":
* Note that the [post condition signal] bits generated at
the output of a compute are before the .sat.
Paragraph about post_zero does not mention saturation, but
testing it on actual GPUs shows that conditional modifiers
are applied after saturation.
* post_zero bit: This bit reflects whether the final
result is zero after all the clamping, normalizing,
or format conversion logic.
For signed types we don't care about saturation: it won't
change the result of conditional modifier.
For floating and unsigned types there two special cases,
when we can remove inst even if scan_inst is saturated: G
and LE. Since conditional modifiers are just comparations
against zero, saturating positive values to the upper
limit never changes the result of comparation.
For negative values:
(sat(x) > 0) == (x > 0) --- false
(sat(x) <= 0) == (x <= 0) --- true
Closes: https://gitlab.freedesktop.org/mesa/mesa/issues/2610
Signed-off-by: Yevhenii Kolesnikov <yevhenii.kolesnikov@globallogic.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4167>
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