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

[Craig Topper via llvm-commits]

topperc 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. 
> 
> 

My point is that there should be some other test change that proves that this patch does something useful. Making a change and then another change to undo the only observed effect doesn't seem useful by itself.

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