https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91683
--- Comment #5 from Jim Wilson <wilson at gcc dot gnu.org> --- (In reply to Richard Biener from comment #3) > Hmm, but shouldn't we instead fix combine to record not the reg rtx but the > regno for UNDO_MODE? Because nothing prevents this from happening elsewhere > (even in combine itself?). Combine doesn't call gen_reg_rtx, other than make_more_copies, and splitters aren't supposed to either. As Segher mentioned, if a define_split needs a temporary it is supposed to add a clobber of a match_operand. I tried an experiment, I set a global var at the start of combine_instructions, cleared it at the end, added an abort to gen_reg_rtx if the var is set, and did an x86 bootstrap. It completed successfully. A make check is running, but I don't expect to hit the abort there either. A RISC-V toolchain with my proposed fix added still fails as riscv_split_symbol called from gen_split_13 has the same problem and needs a similar fix.
