Mesa 20.1 Sees Big Optimizations To Its Soft FP64 Implementation

Written by Michael Larabel in Mesa on 19 March 2020 at 04:00 AM EDT. 8 Comments
For the past year Mesa has offered a "soft" implementation of FP64 capabilities for GPUs lacking FP64 hardware capabilities in order to support ARB_gpu_shader_fp64 as required by OpenGL 4.0. Optimizations were merged today to significantly enhance the "soft FP64" capabilities of Mesa.

Longtime Intel Linux graphics driver developer Ian Romanick merged his set of 30 patches today to improve the compilation performance of FP64-based tests for platforms relying upon this software fallback. Mesa's existing soft FP64 implementation had a lot of control flow to deal with on the GPUs and this new revision seeks to reduce that in making it more GPU-friendly. Various micro-optimizations were also carried out around the NIR portion.

The improvements are looking quite good as with tests carried out by Ian they went from 97.6k instructions generated down to 67.5k instructions. The spilling also dropped from 398 to 365 and the number of fills were also reduced.

In turn this compilation performance work helps run the OpenGL Conformance Test Suite (GL CTS) cases much quicker when testing the soft FP64 code path.

More details via this merge request now honored for next quarter's Mesa 20.1.
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