https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105231
--- Comment #25 from Richard Biener <rguenth at gcc dot gnu.org> --- (In reply to Segher Boessenkool from comment #24) > Wrt keeping REG_EQUAL notes... If you want to keep them you need to make > sure > they still are valid. GCC keeps those on i3, it is much too hard in general > to > validate other such notes. It seems to be that the REG_EQUAL notes of the SET dests in the final instruction we combine into, so 24 for Trying 78, 17 -> 24: are better always valid even after the combination - at least when they are not refering to pseudos set by insns combined (78, 17 here) and always when the REG_EQUAL is constant. When there are multiple sets in the final insn (24) then which note ends up where is determined by the SET dests. For this particular case preserving _constant_ REG_EQUAL notes would be important. And for this case only handling single-set would be good enough. Of course if i3 is not always '24' (in this case) then we have to find a better place to preserve these than distribute_notes.
