Richard Biener <richard.guent...@gmail.com> writes: > On Tue, Feb 20, 2018 at 5:53 PM, Richard Sandiford > <richard.sandif...@linaro.org> wrote: >> This patch prevents pattern-matching of fold-left SLP reduction chains, >> which the previous patch for 83965 didn't handle properly. It only >> stops the last statement in the group from being matched, but that's >> enough to cause the group to be dissolved later. >> >> A better fix would be to put all the information about the reduction >> on the the first statement in the reduction chain, so that every >> statement in the group can tell what the group is doing. That doesn't >> seem like stage 4 material though. >> >> As it stands, things seem to be a bit of a mess. In >> vect_force_simple_reduction we attach the reduction type and >> phi pointer to the last statement in a reduction chain: >> >> reduc_def_info = vinfo_for_stmt (def); >> STMT_VINFO_REDUC_TYPE (reduc_def_info) = v_reduc_type; >> STMT_VINFO_REDUC_DEF (reduc_def_info) = phi; >> >> and mark it as vect_reduction_type in vect_analyze_scalar_cycles_1: >> >> STMT_VINFO_DEF_TYPE (vinfo_for_stmt (reduc_stmt)) = >> >> vect_reduction_def; >> >> This code in vectorizable_reduction gave the impression that >> everything really is keyed off the last statement: >> >> /* In case of reduction chain we switch to the first stmt in the chain, but >> we don't update STMT_INFO, since only the last stmt is marked as >> reduction >> and has reduction properties. */ >> if (GROUP_FIRST_ELEMENT (stmt_info) >> && GROUP_FIRST_ELEMENT (stmt_info) != stmt) >> { >> stmt = GROUP_FIRST_ELEMENT (stmt_info); >> first_p = false; >> } >> >> But this code is dead these days. GROUP_FIRST_ELEMENT is only nonnull >> for SLP reduction chains, since we dissolve the group if SLP fails. >> And SLP only analyses the first statement in the group, not the last: >> >> stmt = SLP_TREE_SCALAR_STMTS (node)[0]; >> stmt_vec_info stmt_info = vinfo_for_stmt (stmt); >> [...] >> bool res = vect_analyze_stmt (stmt, &dummy, node, node_instance); >> >> So from that point of view the DEF_TYPE, REDUC_TYPE and REDUC_DEF >> are being attached to the wrong statement, since we only analyse >> the first one. But it turns out that REDUC_TYPE and REDUC_DEF >> don't matter for the first statement in the group, since that >> takes the phi as an input, and when the phi is a direct input, >> we use *its* REDUC_TYPE and REDUC_DEF instead of the statement's >> own info. The DEF_TYPE problem is handled by: >> >> /* Mark the first element of the reduction chain as reduction to >> properly >> transform the node. In the reduction analysis phase only the last >> element of the chain is marked as reduction. */ >> if (!STMT_VINFO_GROUPED_ACCESS (vinfo_for_stmt (stmt))) >> STMT_VINFO_DEF_TYPE (vinfo_for_stmt (stmt)) = vect_reduction_def; >> >> in vect_analyze_slp_instance (cancelled by: >> >> STMT_VINFO_DEF_TYPE (vinfo_for_stmt (first_element)) >> = vect_internal_def; >> >> in vect_analyze_slp on failure), with the operation being repeated >> in vect_schedule_slp_instance (redundantly AFAICT): >> >> /* Mark the first element of the reduction chain as reduction to properly >> transform the node. In the analysis phase only the last element of the >> chain is marked as reduction. */ >> if (GROUP_FIRST_ELEMENT (stmt_info) && !STMT_VINFO_GROUPED_ACCESS >> (stmt_info) >> && GROUP_FIRST_ELEMENT (stmt_info) == stmt) >> { >> STMT_VINFO_DEF_TYPE (stmt_info) = vect_reduction_def; >> STMT_VINFO_TYPE (stmt_info) = reduc_vec_info_type; >> } >> >> Tested on aarch64-linux-gnu, x86_64-linux-gnu and powerpc64-linux-gnu. >> OK to install? > > Ok for stage1.
It's a GCC 8 regression, so OK for stage4? Richard > Richard. > >> Richard >> >> >> 2018-02-20 Richard Sandiford <richard.sandif...@linaro.org> >> >> gcc/ >> PR tree-optimization/83965 >> * tree-vect-patterns.c (vect_reassociating_reduction_p): Assume >> that grouped statements are part of a reduction chain. Return >> true if the statement is not marked as a reduction itself but >> is part of a group. >> (vect_recog_dot_prod_pattern): Don't check whether the statement >> is part of a group here. >> (vect_recog_sad_pattern): Likewise. >> (vect_recog_widen_sum_pattern): Likewise. >> >> gcc/testsuite/ >> PR tree-optimization/83965 >> * gcc.dg/vect/pr83965-2.c: New test. >> >> Index: gcc/tree-vect-patterns.c >> =================================================================== >> --- gcc/tree-vect-patterns.c 2018-02-20 09:40:41.843451227 +0000 >> +++ gcc/tree-vect-patterns.c 2018-02-20 16:28:55.636762056 +0000 >> @@ -222,13 +222,16 @@ vect_recog_temp_ssa_var (tree type, gimp >> } >> >> /* Return true if STMT_VINFO describes a reduction for which reassociation >> - is allowed. */ >> + is allowed. If STMT_INFO is part of a group, assume that it's part of >> + a reduction chain and optimistically assume that all statements >> + except the last allow reassociation. */ >> >> static bool >> vect_reassociating_reduction_p (stmt_vec_info stmt_vinfo) >> { >> return (STMT_VINFO_DEF_TYPE (stmt_vinfo) == vect_reduction_def >> - && STMT_VINFO_REDUC_TYPE (stmt_vinfo) != FOLD_LEFT_REDUCTION); >> + ? STMT_VINFO_REDUC_TYPE (stmt_vinfo) != FOLD_LEFT_REDUCTION >> + : GROUP_FIRST_ELEMENT (stmt_vinfo) != NULL); >> } >> >> /* Function vect_recog_dot_prod_pattern >> @@ -350,8 +353,7 @@ vect_recog_dot_prod_pattern (vec<gimple >> { >> gimple *def_stmt; >> >> - if (!vect_reassociating_reduction_p (stmt_vinfo) >> - && ! STMT_VINFO_GROUP_FIRST_ELEMENT (stmt_vinfo)) >> + if (!vect_reassociating_reduction_p (stmt_vinfo)) >> return NULL; >> oprnd0 = gimple_assign_rhs1 (last_stmt); >> oprnd1 = gimple_assign_rhs2 (last_stmt); >> @@ -571,8 +573,7 @@ vect_recog_sad_pattern (vec<gimple *> *s >> { >> gimple *def_stmt; >> >> - if (!vect_reassociating_reduction_p (stmt_vinfo) >> - && ! STMT_VINFO_GROUP_FIRST_ELEMENT (stmt_vinfo)) >> + if (!vect_reassociating_reduction_p (stmt_vinfo)) >> return NULL; >> plus_oprnd0 = gimple_assign_rhs1 (last_stmt); >> plus_oprnd1 = gimple_assign_rhs2 (last_stmt); >> @@ -1256,8 +1257,7 @@ vect_recog_widen_sum_pattern (vec<gimple >> if (gimple_assign_rhs_code (last_stmt) != PLUS_EXPR) >> return NULL; >> >> - if (!vect_reassociating_reduction_p (stmt_vinfo) >> - && ! STMT_VINFO_GROUP_FIRST_ELEMENT (stmt_vinfo)) >> + if (!vect_reassociating_reduction_p (stmt_vinfo)) >> return NULL; >> >> oprnd0 = gimple_assign_rhs1 (last_stmt); >> Index: gcc/testsuite/gcc.dg/vect/pr83965-2.c >> =================================================================== >> --- /dev/null 2018-02-19 19:34:42.906488063 +0000 >> +++ gcc/testsuite/gcc.dg/vect/pr83965-2.c 2018-02-20 >> 16:28:55.635762095 +0000 >> @@ -0,0 +1,16 @@ >> +/* { dg-do compile } */ >> +/* { dg-additional-options "-Ofast -ftrapv" } */ >> + >> +int c; >> +unsigned char d; >> +int e (unsigned char *f) >> +{ >> + int g; >> + for (int a; a; a++) >> + { >> + for (int b = 0; b < 6; b++) >> + g += __builtin_abs (f[b] - d); >> + f += c; >> + } >> + return g; >> +}