tree 52e87d98f2e7de911431df9d96e8a797f9ba64f6
parent 3b1c511b099e88d1b153de784e3bf7e951a6288f
author Iago Toral Quiroga <itoral@igalia.com> 1593078844 +0200
committer Iago Toral <itoral@igalia.com> 1593161852 +0000

v3d/compiler: don't rewrite unused temporaries to point to NOP register

This was assuming that unused temporaries are written but never read,
since the NOP register can only be used as a destination register,
but we can end up here also for temporaries that are read once but
never written.

This was found with a graphicsfuzz test that has a switch with
cases that have unreachable discards. In that test, NIR genrates
code like this:

decl_reg vec3 32 r19
...
r20 = mov r19.z
r21 = mov r19.y
r22 = mov r19.x

Where r19.xyz would generate 3 temporary registers that are read but
never written, so we would rewrite them to point to the NOP register
as QPU instruction sources, which is not allowed and would hit an
assert that expect magic reads to be from [r0,r5] only.

Fixes:
dEQP-VK.graphicsfuzz.unreachable-switch-case-with-discards

Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5645>