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

[segher at gcc dot gnu.org]

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

--- Comment #17 from Segher Boessenkool <segher at gcc dot gnu.org> ---
I'll do a patch to prohibit gen_reg_rtx inside combine, btw...  Let's see
how far that goes.