On Tue, Dec 09, 2014 at 12:15:30PM -0700, Jeff Law wrote: > >>@@ -3323,7 +3396,11 @@ try_combine (rtx_insn *i3, rtx_insn *i2, rtx_insn > >>*i1, rtx_insn *i0, > >> rtx old = newpat; > >> total_sets = 1 + extra_sets; > >> newpat = gen_rtx_PARALLEL (VOIDmode, rtvec_alloc (total_sets)); > >>- XVECEXP (newpat, 0, 0) = old; > >>+ > >>+ if (to_combined_insn) > >>+ XVECEXP (newpat, 0, --total_sets) = old; > >>+ else > >>+ XVECEXP (newpat, 0, 0) = old; > >> } > > > >Is this correct? If so, it needs a big fat comment, because it is > >not exactly obvious :-) > > > >Also, it doesn't handle at all the case where the new pattern already is > >a PARALLEL; can that never happen? > I'd convinced myself it was. But yes, a comment here would be good. > > Presumably you're thinking about a PARALLEL that satisfies single_set_p?
I wasn't thinking about anything in particular; this code does not handle a PARALLEL newpat with to_combined_insn correctly, and it doesn't say it cannot happen. But yes, I don't see why it could not happen? E.g. a parallel of multiple sets with all but one of those dead? Why should it be single_set here anyway? (Maybe I need more coffee, sorry if so). Segher
