[llvm] [ARM] Use `RegisterClassInfo::getRegPressureSetLimit` (PR #120377)

[David Green via llvm-commits]

https://github.com/davemgreen commented:

Thanks for separating this out. ARM has a lot of nested register classes with overlapping registers, and the register pressure calculations for FP have never been very accurate. I always wanted to exclude certain register classes (like the one causing problems here), but doing that has never led to performance improvements overall. The register pressures looks somewhat like a random number generator to be honest, and the TRI version can be closer to reality in some places. We might have to make something that helps this test case for the time being and looks into the wider problem of fp reg-pressure later on.

https://github.com/llvm/llvm-project/pull/120377