The main improvement is to the mfma tests. There are some
mild regressions scattered around, and a few major ones.
The worst regressions are in some of the bitcast tests;
these are cases where the SGPR argument list runs out
and uses VGPRs, and the copies-from-VGPR are misidentified
as divergent. Most of the shufflevector tests are also
regressions. These end up with cleaner MIR, but then get poor
regalloc decisions.
fbf74b2553