[AMDGPU][Scheduler] Consistent occupancy calculation during rematerialization (#149224)

The `RPTarget`'s way of determining whether VGPRs are beneficial to save
and whether the target has been reached w.r.t. VGPR usage currently
assumes, if `CombinedVGPRSavings` is true, that free slots in one VGPR
RC can always be used for the other. Implicitly, this makes the
rematerialization stage (only current user of `RPTarget`) follow a
different occupancy calculation than the "regular one" that the
scheduler uses, one that assumes that ArchVGPR/AGPR usage can be
balanced perfectly and at no cost, which is untrue in general. This
ultimately yields suboptimal rematerialization decisions that require
cross-VGPR-RC copies unnecessarily.

This fixes that, making the `RPTarget`'s internal model of occupancy
consistent with the regular one. The `CombinedVGPRSavings` flag is
removed, and a form of cross-VGPR-RC saving implemented only for unified
RFs, which is where it makes the most sense. Only when the amount of
free VGPRs in a given VGPR RC (ArchVPGR or AGPR) is lower than the
excess VGPR usage in the other VGPR RC does the `RPTarget` consider that
a pressure reduction in the former will be beneficial to the latter.

0 files changed, 0 insertions, 0 deletions