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On V3D the quality of the code we generate is significantly affected by how we decide to assign accumulators during register allocation, which is determined by liveness, favoring short-lived temps. There are many shaders that end up doing a whole lot of uniform loads first, and using them later, which is very inconvenient for our register allocation process because this increases uniform liveness and causes us to use accumulators less efficientely, leading to significant churn. To fix this, we move uniforms right before their first use in the same block, but we need to do this after NIR scheduling, which means we are doing it in non-SSA form, since the scheduler has a tendency to undo this optimization and it is not easy to modify it to avoid it, since it works in more abstract terms, using instruction dependencies, estimated register pressure and instruction delay information to do its work, which are very different concepts. total instructions in shared programs: 13316738 -> 13033613 (-2.13%) instructions in affected programs: 10389172 -> 10106047 (-2.73%) helped: 55442 HURT: 16144 total threads in shared programs: 413722 -> 415048 (0.32%) threads in affected programs: 1428 -> 2754 (92.86%) helped: 680 HURT: 17 total loops in shared programs: 1716 -> 1690 (-1.52%) loops in affected programs: 26 -> 0 helped: 26 HURT: 0 total uniforms in shared programs: 3704313 -> 3705181 (0.02%) uniforms in affected programs: 687730 -> 688598 (0.13%) helped: 2920 HURT: 7384 total max-temps in shared programs: 2364785 -> 2175190 (-8.02%) max-temps in affected programs: 1215387 -> 1025792 (-15.60%) helped: 49667 HURT: 1556 total spills in shared programs: 4241 -> 4248 (0.17%) spills in affected programs: 642 -> 649 (1.09%) helped: 11 HURT: 19 total fills in shared programs: 6115 -> 6125 (0.16%) fills in affected programs: 1276 -> 1286 (0.78%) helped: 11 HURT: 21 total sfu-stalls in shared programs: 34381 -> 36578 (6.39%) sfu-stalls in affected programs: 16055 -> 18252 (13.68%) helped: 3647 HURT: 5206 Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com> Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15056> |
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