[Bug target/91683] ICE: SIGSEGV at -O when compiling for riscv64

[wilson at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91683

--- Comment #14 from Jim Wilson <wilson at gcc dot gnu.org> ---
> 3) Do we want to prohibit calling gen_reg_rtx during combine?  Why did
> we want it, before?

Prohibiting gen_reg_rtx calls here would have helped find the bugs I'm fixing
now.  I've got a hack to do this to find the remaining bugs I need to fix.

I don't know why anyone would want it before.  I'm not sure if this ever worked
right.