[ack_complete]

Looks like many x86 cores still do rename MXCSR, though Gracemont notably doesn't: https://chipsandcheese.com/2021/12/21/gracemont-revenge-of-t...

Note that you wouldn't necessarily need to do a read-modify-write -- it'd suffice in most cases to just to save the old value and then reset the whole MXCSR for the scope requiring special treatment.

[titzer]

Also worth noting that it's not the entire MXCSR that needs to be renamed, but just a handful of status bits, so the logic is likely even cheaper than renaming a GPR.