This pass detects potential loop terminators and moves intructions
from the non breaking branch after the if-statement.
This enables both the new opt_if_simplification() pass and loop
unrolling to potentially progress further.
Unexpectedly this change speed up shader-db run times by ~3%
Ivy Bridge shader-db results (all changes in dolphin/ubershaders):
total instructions in shared programs: 9995662 -> 9995338 (-0.00%)
instructions in affected programs: 87845 -> 87521 (-0.37%)
helped: 27
HURT: 0
total cycles in shared programs: 230931495 -> 230925015 (-0.00%)
cycles in affected programs: 56391385 -> 56384905 (-0.01%)
helped: 27
HURT: 0
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
This pass turns:
if (cond) {
} else {
do_work();
}
into:
if (!cond) {
do_work();
} else {
}
Here's the vkpipeline-db stats (from affected shaders) on Polaris10:
Totals from affected shaders:
SGPRS: 17272 -> 17296 (0.14 %)
VGPRS: 18712 -> 18740 (0.15 %)
Spilled SGPRs: 1179 -> 1142 (-3.14 %)
Code Size: 1503364 -> 1515176 (0.79 %) bytes
Max Waves: 916 -> 911 (-0.55 %)
This pass only affects Serious Sam 2017 (Vulkan) on my side. The
stats are not really good for now. Some shaders look quite dumb
but this will be improved with further NIR passes, like ifs
combination.
Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
When shaders come in from SPIR-V, we handle continue blocks by placing
the contents of the continue inside of a "if (!first_iteration)". We do
this so that we can properly handle the fact that continues in SPIR-V
jump to the continue block at the end of the loop rather than jumping
directly to the top of the loop like they do in NIR. In particular, the
increment step of a simple for loop ends up in the continue block. This
pass looks for this case in loops that don't actually have any continues
and moves the continue contents to the end of the loop instead. We need
this because loop unrolling doesn't work if the increment is inside of a
condition.
Reviewed-by: Timothy Arceri <timothy.arceri@collabora.com>
