[llvm] [X86] Resolve FIXME: Add FPCW as a rounding control register (PR #82452)

[via llvm-commits]

AtariDreams wrote:

> Is it possible to test this change? I don't know what `getRoundingControlRegisters`  is used for.

It's for adding those registers to the usedregs array so they aren't marked as killed between function calls. 

This had the side effect of causing the wait insertion pass to not consider call sites as places to insert wait before, so as a result I'm sure other workarounds had to be done. 



https://github.com/llvm/llvm-project/pull/82452