Kenneth Graunke
fc0aaa81ee
Originally written by Ian Romanick for the Intel backend, but ported
to the new nir_opt_barrier_modes() common optimization pass. Ian's
original explanation and commit message follows:
Shared memory only exists within a workgroup, so synchronizing it beyond
workgroup scope is nonsense.
Basically every SPIR-V compiler generates operations like
OpMemoryBarrier(/*Memory*/Device,
/*Semantics*/AcquireRelease | WorkgroupMemory)
This is suggested in numerous places, including
https://github.com/KhronosGroup/GLSL/blob/master/extensions/khr/GL_KHR_vulkan_glsl.txt.
Even Mesa's glsl_to_nir pass does this. This advice, which has been
copy-and-pasted everywhere, is contrary to issue 13 in the original
GL_ARB_compute_shader spec:
"Since shared memory is only accessible to threads within a single
work group, memoryBarrierShared() also only requires synchronization
with other threads in the same work group."
Reviewed-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24842>
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