Hi, Gentle ping this:
https://gcc.gnu.org/pipermail/gcc-patches/2021-September/580358.html BR, Kewen > on 2021/9/28 下午4:16, Kewen.Lin via Gcc-patches wrote: >> Hi, >> >> This patch follows the discussions here[1][2], where Segher >> pointed out the existing way to guard the extra penalized >> cost for strided/elementwise loads with a magic bound does >> not scale. >> >> The way with nunits * stmt_cost can get one much >> exaggerated penalized cost, such as: for V16QI on P8, it's >> 16 * 20 = 320, that's why we need one bound. To make it >> better and more readable, the penalized cost is simplified >> as: >> >> unsigned adjusted_cost = (nunits == 2) ? 2 : 1; >> unsigned extra_cost = nunits * adjusted_cost; >> >> For V2DI/V2DF, it uses 2 penalized cost for each scalar load >> while for the other modes, it uses 1. It's mainly concluded >> from the performance evaluations. One thing might be >> related is that: More units vector gets constructed, more >> instructions are used. It has more chances to schedule them >> better (even run in parallelly when enough available units >> at that time), so it seems reasonable not to penalize more >> for them. >> >> The SPEC2017 evaluations on Power8/Power9/Power10 at option >> sets O2-vect and Ofast-unroll show this change is neutral. >> >> Bootstrapped and regress-tested on powerpc64le-linux-gnu Power9. >> >> Is it ok for trunk? >> >> [1] https://gcc.gnu.org/pipermail/gcc-patches/2021-September/579121.html >> [2] https://gcc.gnu.org/pipermail/gcc-patches/2021-September/580099.html >> v1: https://gcc.gnu.org/pipermail/gcc-patches/2021-September/579529.html >> >> BR, >> Kewen >> ----- >> gcc/ChangeLog: >> >> * config/rs6000/rs6000.c (rs6000_update_target_cost_per_stmt): Adjust >> the way to compute extra penalized cost. Remove useless parameter. >> (rs6000_add_stmt_cost): Adjust the call to function >> rs6000_update_target_cost_per_stmt. >> >> >> --- >> gcc/config/rs6000/rs6000.c | 31 ++++++++++++++++++------------- >> 1 file changed, 18 insertions(+), 13 deletions(-) >> >> diff --git a/gcc/config/rs6000/rs6000.c b/gcc/config/rs6000/rs6000.c >> index dd42b0964f1..8200e1152c2 100644 >> --- a/gcc/config/rs6000/rs6000.c >> +++ b/gcc/config/rs6000/rs6000.c >> @@ -5422,7 +5422,6 @@ rs6000_update_target_cost_per_stmt (rs6000_cost_data >> *data, >> enum vect_cost_for_stmt kind, >> struct _stmt_vec_info *stmt_info, >> enum vect_cost_model_location where, >> - int stmt_cost, >> unsigned int orig_count) >> { >> >> @@ -5462,17 +5461,23 @@ rs6000_update_target_cost_per_stmt (rs6000_cost_data >> *data, >> { >> tree vectype = STMT_VINFO_VECTYPE (stmt_info); >> unsigned int nunits = vect_nunits_for_cost (vectype); >> - unsigned int extra_cost = nunits * stmt_cost; >> - /* As function rs6000_builtin_vectorization_cost shows, we have >> - priced much on V16QI/V8HI vector construction as their units, >> - if we penalize them with nunits * stmt_cost, it can result in >> - an unreliable body cost, eg: for V16QI on Power8, stmt_cost >> - is 20 and nunits is 16, the extra cost is 320 which looks >> - much exaggerated. So let's use one maximum bound for the >> - extra penalized cost for vector construction here. */ >> - const unsigned int MAX_PENALIZED_COST_FOR_CTOR = 12; >> - if (extra_cost > MAX_PENALIZED_COST_FOR_CTOR) >> - extra_cost = MAX_PENALIZED_COST_FOR_CTOR; >> + /* Don't expect strided/elementwise loads for just 1 nunit. */ >> + gcc_assert (nunits > 1); >> + /* i386 port adopts nunits * stmt_cost as the penalized cost >> + for this kind of penalization, we used to follow it but >> + found it could result in an unreliable body cost especially >> + for V16QI/V8HI modes. To make it better, we choose this >> + new heuristic: for each scalar load, we use 2 as penalized >> + cost for the case with 2 nunits and use 1 for the other >> + cases. It's without much supporting theory, mainly >> + concluded from the broad performance evaluations on Power8, >> + Power9 and Power10. One possibly related point is that: >> + vector construction for more units would use more insns, >> + it has more chances to schedule them better (even run in >> + parallelly when enough available units at that time), so >> + it seems reasonable not to penalize that much for them. */ >> + unsigned int adjusted_cost = (nunits == 2) ? 2 : 1; >> + unsigned int extra_cost = nunits * adjusted_cost; >> data->extra_ctor_cost += extra_cost; >> } >> } >> @@ -5510,7 +5515,7 @@ rs6000_add_stmt_cost (class vec_info *vinfo, void >> *data, int count, >> cost_data->cost[where] += retval; >> >> rs6000_update_target_cost_per_stmt (cost_data, kind, stmt_info, where, >> - stmt_cost, orig_count); >> + orig_count); >> } >> >> return retval; >> -- >> 2.27.0 >>
