bbde792786
Allow widening up to 128-bit registers or if the new register class is at least as large as one of the existing register classes. This was artificially limiting. In particular this was doing the wrong thing with sequences involving copies between VGPRs and AV registers. Nearly all test changes are improvements. The coalescer does not just widen registers out of nowhere. If it's trying to "widen" a register, it's generally packing a register into an existing register tuple, or in a situation where the constraints imply the wider class anyway. 067a11015 addressed the allocation failure concern by rejecting coalescing if there are no available registers. The original change in a4e63ead4b didn't include a realistic testcase to judge if this is harmful for pressure. I would expect any issues from this to be of garden variety subreg handling issue. We could use more dynamic state information here if it really is an issue. I get the best results by removing this override completely. This is a smaller step for patch splitting purposes.
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