[Bug rtl-optimization/87507] IRA unnecessarily uses non-volatile registers during register assignment

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87507

--- Comment #9 from Segher Boessenkool <segher at gcc dot gnu.org> ---
Why isn't this handled in subreg1 already?  Sorry if that is obvious :-)