On October 16, 2014 7:26:48 PM CEST, Jeff Law <l...@redhat.com> wrote: >On 10/16/14 08:11, Marc Glisse wrote: > >> >> I am looking into that, it must be doable. It seems not too hard, in >> maybe_register_def, to push all results from make_ssa_name to some >> data-structure (I don't think new_ssa_names gives me that list, but >> there may be other ways to get it without introducing yet another >list), >> and either mark them as used in maybe_replace_use or >get_reaching_def, >> or better loop through them at the end, checking has_zero_uses (it is >a >> bit wasteful, only those coming from clobbers may have 0 uses (or we >> missed a dce/dse earlier), but it should be fast enough, even walking >on >> all ssa_names should be fast enough). If we go to that much trouble, >we >> may as well clean them while we are there. It isn't obvious to me how >to >> notice unused new ssa_names more easily, to trigger a DCE. >I'd walk the SSA_NAMEs at the end checking for zero uses. I'm curious >how often that will trigger :-)
Most often for the initial into SSA I guess. After that only for the cases we rename a variable which does not happen often. SRA and update-address-taken cone to my mind. BTW, I dislike having multiple DCE implementations... Richard. >jeff
