On Thu, Oct 13, 2016 at 5:38 PM, Bill Schmidt <wschm...@linux.vnet.ibm.com> wrote: > The previous patch for > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77937 is necessary, but not > sufficient in all cases. It allows -1 to be used with a pointer > increment, which we really do not want given that this is generally not > profitable. Disable this case for now. We can add logic later to > estimate the cost for the rare case where it can be useful. > > Bootstrapped and tested on powerpc64le-unknown-linux-gnu with no > regressions, committed.
Huh, I wonder what is special about -1 here. Do we handle -2? Richard. > Thanks, > Bill > > > 2016-10-13 Bill Schmidt <wschm...@linux.vnet.ibm.com> > > PR tree-optimization/77937 > * gimple-ssa-strength-reduction.c (analyze_increments): Set cost > to infinite when we have a pointer with an increment of -1. > > > Index: gcc/gimple-ssa-strength-reduction.c > =================================================================== > --- gcc/gimple-ssa-strength-reduction.c (revision 241120) > +++ gcc/gimple-ssa-strength-reduction.c (working copy) > @@ -2818,6 +2818,11 @@ analyze_increments (slsr_cand_t first_dep, machine > || (incr == -1 > && !POINTER_TYPE_P (first_dep->cand_type))) > incr_vec[i].cost = COST_NEUTRAL; > + > + /* FIXME: We don't handle pointers with a -1 increment yet. > + They are usually unprofitable anyway. */ > + else if (incr == -1 && POINTER_TYPE_P (first_dep->cand_type)) > + incr_vec[i].cost = COST_INFINITE; > > /* FORNOW: If we need to add an initializer, give up if a cast from > the candidate's type to its stride's type can lose precision. > >
