[Bug rtl-optimization/92107] GCC's insn attribute arithmetic does not follow C rules

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92107

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
it doesn't have to be anything to do with C rules, it's simply an incorrect
transcription of lispy arithmetic to C?