Instructions that operate on an array read the previous state of the
array, modify it, and write a new array, at least conceptually before
RA. Previously the same register specified the previous state and acted
as the new state, but this meant that it was both a source and
destination which meant that it was getting in the way of splitting up
sources and destinations. Break out the source into a separate register,
and use the new tied-src infrastructure to share code with a6xx atomics.
With this, there are basically no more special cases for arrays in RA.
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11469>
This will be run right after nir->ir3. Even though we have SSA coming
out of NIR, we still need it for NIR registers, even though we keep the
original array around to insert false dependencies.
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9842>
Connor Abbott