https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79390
--- Comment #23 from Richard Biener <rguenth at gcc dot gnu.org> --- (In reply to Richard Biener from comment #22) > (In reply to rguent...@suse.de from comment #21) > > On April 7, 2017 6:57:13 PM GMT+02:00, "jakub at gcc dot gnu.org" > > <gcc-bugzi...@gcc.gnu.org> wrote: > > >https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79390 > > > > > >--- Comment #20 from Jakub Jelinek <jakub at gcc dot gnu.org> --- > > >So, Richard, any thoughts on what can be done split paths to avoid > > >this? > > > > Invent some new heuristic that avoids splitting this case... > > Index: gcc/gimple-ssa-split-paths.c > =================================================================== > --- gcc/gimple-ssa-split-paths.c (revision 246803) > +++ gcc/gimple-ssa-split-paths.c (working copy) > @@ -249,13 +249,17 @@ is_feasible_trace (basic_block bb) > imm_use_iterator iter2; > FOR_EACH_IMM_USE_FAST (use2_p, iter2, gimple_phi_result > (stmt)) > { > - if (is_gimple_debug (USE_STMT (use2_p))) > + gimple *use_stmt = USE_STMT (use2_p); > + if (is_gimple_debug (use_stmt)) > continue; > - basic_block use_bb = gimple_bb (USE_STMT (use2_p)); > + basic_block use_bb = gimple_bb (use_stmt); > if (use_bb != bb > && dominated_by_p (CDI_DOMINATORS, bb, use_bb)) > { > - found_useful_phi = true; > + if (gcond *cond = dyn_cast <gcond *> (use_stmt)) > + if (gimple_cond_code (cond) == EQ_EXPR > + || gimple_cond_code (cond) == NE_EXPR) > + found_useful_phi = true; > break; > } > } > > avoids the splitting at at least passes tree-ssa.exp testing. Throwing it > on full testing (there are some path splitting testcases randomly placed > IIRC). Bootstrap / regtest went ok. With this and -O3 -march=native (on a broadwell CPU) I get gcc6 -O3 -march=native: 5469.25 Mflops gcc7 -O3 -march=native: 5439.39 Mflops but note that with -Ofast -march=native the situation is still bad (-fno-split-paths doesn't help but -ftree-loop-if-convert does): gcc6 -Ofast -march=native: 5500.51 Mflops gcc7 -Ofast -march=native: 4765.56 Mflops gcc7 -Ofast -march=native -ftree-loop-if-convert: 5335.49 Mflops Shall I go for the split-path fix for the moment?
