Intel i915g Mesa Driver Now Goes Goes Through NIR, Fixes Some Past Test Failures

While this week's landing of the Crocus Gallium3D driver for Intel Gen4 through Gen7 graphics (i965 through Haswell) in Mesa is exciting for Linux users that are still running aging Intel systems, going back even further has been the i915g Gallium3D driver and there this week there happens to be a big improvement too.

Emma Anholt's work on switching i915g to the NIR-to-TGSI path has been merged. Rather than the i915g going GLSL-to-TGSI as has long been the case, it's now employing the GLSL-to-NIR and NIR-to-TGSI route. In turn, i915g can leverage the common NIR optimizations utilized by other drivers and NIR just being the more modern and popular intermediate representation used by today's Mesa drivers. The Gallium3D TGSI IR is ultimately still used by the i915g driver for now rather than native NIR.

Emma noted in the merge request that in switching to NIR-to-TGSI, it fixes around 10% of the OpenGL ES 2 test failures thanks to using the "better compiler".

This is part of a broader and ongoing push in replacing Mesa GLSL-to-TGSI usage with GLSL-to-NIR and NIR-to-TGSI throughout the other older drivers as well so that Mesa can drop its old GLSL-to-TGSI code.

This is a rare but significant improvement to the i915g driver that is seldom touched these days. No benchmarks are planned as this hardware should just be laid to rest.