The maximum VGPR usage of a shader is limited based on the target
occupancy,
ensuring that the targeted number of waves actually fit onto a CU/WGP.
However, in dynamic VGPR mode, we should not do that, because VGPRs are
allocated
dynamically at runtime, and there are no static constraints based on
occupancy.
Fix that in this patch.
Also fixup the getMinNumVGPRs helper to behave consistently by always
returning
zero in dVGPR mode.
This also fixes a problem where AMDGPUAsmPrinter bumps the VGPR usage to
at least
the result of getMinNumVGPRs, per my understanding in order to avoid an
occupancy
that is higher than the occupancy target. That was causing incorrect
(too high)
VGPR usages in dVGPR mode with medium-sized workgroups (say 768).
6cc0cb69e4