https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106293
--- Comment #4 from luoxhu at gcc dot gnu.org --- Could you try revert (In reply to Richard Biener from comment #2) > I can reproduce a regression with -Ofast -march=znver2 running on Haswell as > well. -fopt-info doesn't reveal anything interesting besides > > -fast_algorithms.c:133:19: optimized: loop with 2 iterations completely > unrolled (header execution count 32987933) > +fast_algorithms.c:133:19: optimized: loop with 2 iterations completely > unrolled (header execution count 129072791) > > obviously the slowdown is in P7Viterbi. There's only minimal changes on the > GIMPLE side, one notable: > > niters_vector_mult_vf.205_2406 = niters.203_442 & 429496729 | _2041 = > niters.203_438 & 3; > _2408 = (int) niters_vector_mult_vf.205_2406; | if (_2041 > == 0) > tmp.206_2407 = k_384 + _2408; | goto <bb > 66>; [25.00%] > _2300 = niters.203_442 & 3; < > if (_2300 == 0) < > goto <bb 65>; [25.00%] < > else else > goto <bb 36>; [75.00%] goto <bb > 36>; [75.00%] > > <bb 36> [local count: 41646173]: | <bb 36> > [local count: 177683003]: > # k_2403 = PHI <tmp.206_2407(35), tmp.239_2637(34)> | > niters_vector_mult_vf.205_2409 = niters.203_438 & 429496729 > # DEBUG k => k_2403 | _2411 = > (int) niters_vector_mult_vf.205_2409; > > > tmp.206_2410 = k_382 + _2411; > > > > <bb 37> > [local count: 162950122]: > > # k_2406 = > PHI <tmp.206_2410(36), tmp.239_2639(34)> > > the sink pass now does the transform where it did not do so before. > > That's appearantly because of > > /* If BEST_BB is at the same nesting level, then require it to have > significantly lower execution frequency to avoid gratuitous movement. > */ > if (bb_loop_depth (best_bb) == bb_loop_depth (early_bb) > /* If result of comparsion is unknown, prefer EARLY_BB. > Thus use !(...>=..) rather than (...<...) */ > && !(best_bb->count * 100 >= early_bb->count * threshold)) > return best_bb; > > /* No better block found, so return EARLY_BB, which happens to be the > statement's original block. */ > return early_bb; > > where the SRC count is 96726596 before, 236910671 after and the > destination count is 72544947 before, 177683003 at the destination after. > The edge probabilities are 75% vs 25% and param_sink_frequency_threshold > is exactly 75 as well. Since 236910671*0.75 > is rounded down it passes the test while the previous state has an exact > match defeating it. > > It's a little bit of an arbitrary choice, > > diff --git a/gcc/tree-ssa-sink.cc b/gcc/tree-ssa-sink.cc > index 2e744d6ae50..9b368e13463 100644 > --- a/gcc/tree-ssa-sink.cc > +++ b/gcc/tree-ssa-sink.cc > @@ -230,7 +230,7 @@ select_best_block (basic_block early_bb, > if (bb_loop_depth (best_bb) == bb_loop_depth (early_bb) > /* If result of comparsion is unknown, prefer EARLY_BB. > Thus use !(...>=..) rather than (...<...) */ > - && !(best_bb->count * 100 >= early_bb->count * threshold)) > + && !(best_bb->count * 100 > early_bb->count * threshold)) > return best_bb; > > /* No better block found, so return EARLY_BB, which happens to be the > > fixes the missed sinking but not the regression :/ > > The count differences start to appear in when LC PHI blocks are added > only for virtuals and then pre-existing 'Invalid sum of incoming counts' > eventually lead to mismatches. The 'Invalid sum of incoming counts' > start with the loop splitting pass. > > fast_algorithms.c:145:10: optimized: loop split > > Xionghu Lou did profile count updates there, not sure if that made things > worse in this case. > > At least with broken BB counts splitting/unsplitting an edge can propagate > bogus counts elsewhere it seems. :(, Could you please try revert cd5ae148c47c6dee05adb19acd6a523f7187be7f and see whether performance is back?
