> -----Original Message-----
> From: Richard Biener <richard.guent...@gmail.com>
> Sent: Friday, May 10, 2024 2:07 PM
> To: Richard Biener <rguent...@suse.de>
> Cc: gcc-patches@gcc.gnu.org
> Subject: Re: [PATCH] Allow patterns in SLP reductions
>
> On Fri, Mar 1, 2024 at 10:21 AM Richard Biener <rguent...@suse.de> wrote:
> >
> > The following removes the over-broad rejection of patterns for SLP
> > reductions which is done by removing them from LOOP_VINFO_REDUCTIONS
> > during pattern detection. That's also insufficient in case the
> > pattern only appears on the reduction path. Instead this implements
> > the proper correctness check in vectorizable_reduction and guides
> > SLP discovery to heuristically avoid forming later invalid groups.
> >
> > I also couldn't find any testcase that FAILs when allowing the SLP
> > reductions to form so I've added one.
> >
> > I came across this for single-lane SLP reductions with the all-SLP
> > work where we rely on patterns to properly vectorize COND_EXPR
> > reductions.
> >
> > Bootstrapped and tested on x86_64-unknown-linux-gnu, queued for stage1.
>
> Re-bootstrapped/tested, r15-361-g52d4691294c847
Awesome!
Does this now allow us to write new reductions using patterns? i.e. widening
reductions?
Cheers,
Tamar
>
> Richard.
>
> > Richard.
> >
> > * tree-vect-patterns.cc (vect_pattern_recog_1): Do not
> > remove reductions involving patterns.
> > * tree-vect-loop.cc (vectorizable_reduction): Reject SLP
> > reduction groups with multiple lane-reducing reductions.
> > * tree-vect-slp.cc (vect_analyze_slp_instance): When discovering
> > SLP reduction groups avoid including lane-reducing ones.
> >
> > * gcc.dg/vect/vect-reduc-sad-9.c: New testcase.
> > ---
> > gcc/testsuite/gcc.dg/vect/vect-reduc-sad-9.c | 68 ++++++++++++++++++++
> > gcc/tree-vect-loop.cc | 15 +++++
> > gcc/tree-vect-patterns.cc | 13 ----
> > gcc/tree-vect-slp.cc | 26 +++++---
> > 4 files changed, 101 insertions(+), 21 deletions(-)
> > create mode 100644 gcc/testsuite/gcc.dg/vect/vect-reduc-sad-9.c
> >
> > diff --git a/gcc/testsuite/gcc.dg/vect/vect-reduc-sad-9.c
> b/gcc/testsuite/gcc.dg/vect/vect-reduc-sad-9.c
> > new file mode 100644
> > index 00000000000..3c6af4510f4
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/vect/vect-reduc-sad-9.c
> > @@ -0,0 +1,68 @@
> > +/* Disabling epilogues until we find a better way to deal with scans. */
> > +/* { dg-additional-options "--param vect-epilogues-nomask=0" } */
> > +/* { dg-additional-options "-msse4.2" { target { x86_64-*-* i?86-*-* } } }
> > */
> > +/* { dg-require-effective-target vect_usad_char } */
> > +
> > +#include <stdarg.h>
> > +#include "tree-vect.h"
> > +
> > +#define N 64
> > +
> > +unsigned char X[N] __attribute__ ((__aligned__(__BIGGEST_ALIGNMENT__)));
> > +unsigned char Y[N] __attribute__ ((__aligned__(__BIGGEST_ALIGNMENT__)));
> > +int abs (int);
> > +
> > +/* Sum of absolute differences between arrays of unsigned char types.
> > + Detected as a sad pattern.
> > + Vectorized on targets that support sad for unsigned chars. */
> > +
> > +__attribute__ ((noinline)) int
> > +foo (int len, int *res2)
> > +{
> > + int i;
> > + int result = 0;
> > + int result2 = 0;
> > +
> > + for (i = 0; i < len; i++)
> > + {
> > + /* Make sure we are not using an SLP reduction for this. */
> > + result += abs (X[2*i] - Y[2*i]);
> > + result2 += abs (X[2*i + 1] - Y[2*i + 1]);
> > + }
> > +
> > + *res2 = result2;
> > + return result;
> > +}
> > +
> > +
> > +int
> > +main (void)
> > +{
> > + int i;
> > + int sad;
> > +
> > + check_vect ();
> > +
> > + for (i = 0; i < N/2; i++)
> > + {
> > + X[2*i] = i;
> > + Y[2*i] = N/2 - i;
> > + X[2*i+1] = i;
> > + Y[2*i+1] = 0;
> > + __asm__ volatile ("");
> > + }
> > +
> > +
> > + int sad2;
> > + sad = foo (N/2, &sad2);
> > + if (sad != (N/2)*(N/4))
> > + abort ();
> > + if (sad2 != (N/2-1)*(N/2)/2)
> > + abort ();
> > +
> > + return 0;
> > +}
> > +
> > +/* { dg-final { scan-tree-dump "vect_recog_sad_pattern: detected" "vect" }
> > } */
> > +/* { dg-final { scan-tree-dump-times "vectorized 1 loops" 1 "vect" } } */
> > +
> > diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
> > index 35f1f8c7d42..13dcdba403a 100644
> > --- a/gcc/tree-vect-loop.cc
> > +++ b/gcc/tree-vect-loop.cc
> > @@ -7703,6 +7703,21 @@ vectorizable_reduction (loop_vec_info loop_vinfo,
> > return false;
> > }
> >
> > + /* Lane-reducing ops also never can be used in a SLP reduction group
> > + since we'll mix lanes belonging to different reductions. But it's
> > + OK to use them in a reduction chain or when the reduction group
> > + has just one element. */
> > + if (lane_reduc_code_p
> > + && slp_node
> > + && !REDUC_GROUP_FIRST_ELEMENT (stmt_info)
> > + && SLP_TREE_LANES (slp_node) > 1)
> > + {
> > + if (dump_enabled_p ())
> > + dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
> > + "lane-reducing reduction in reduction group.\n");
> > + return false;
> > + }
> > +
> > /* All uses but the last are expected to be defined in the loop.
> > The last use is the reduction variable. In case of nested cycle this
> > assumption is not true: we use reduc_index to record the index of the
> > diff --git a/gcc/tree-vect-patterns.cc b/gcc/tree-vect-patterns.cc
> > index d562f57920f..fe1ffba8688 100644
> > --- a/gcc/tree-vect-patterns.cc
> > +++ b/gcc/tree-vect-patterns.cc
> > @@ -7172,7 +7172,6 @@ vect_pattern_recog_1 (vec_info *vinfo,
> > vect_recog_func *recog_func, stmt_vec_info stmt_info)
> > {
> > gimple *pattern_stmt;
> > - loop_vec_info loop_vinfo;
> > tree pattern_vectype;
> >
> > /* If this statement has already been replaced with pattern statements,
> > @@ -7198,8 +7197,6 @@ vect_pattern_recog_1 (vec_info *vinfo,
> > return;
> > }
> >
> > - loop_vinfo = dyn_cast <loop_vec_info> (vinfo);
> > -
> > /* Found a vectorizable pattern. */
> > if (dump_enabled_p ())
> > dump_printf_loc (MSG_NOTE, vect_location,
> > @@ -7208,16 +7205,6 @@ vect_pattern_recog_1 (vec_info *vinfo,
> >
> > /* Mark the stmts that are involved in the pattern. */
> > vect_mark_pattern_stmts (vinfo, stmt_info, pattern_stmt,
> > pattern_vectype);
> > -
> > - /* Patterns cannot be vectorized using SLP, because they change the
> > order of
> > - computation. */
> > - if (loop_vinfo)
> > - {
> > - unsigned ix, ix2;
> > - stmt_vec_info *elem_ptr;
> > - VEC_ORDERED_REMOVE_IF (LOOP_VINFO_REDUCTIONS (loop_vinfo), ix,
> ix2,
> > - elem_ptr, *elem_ptr == stmt_info);
> > - }
> > }
> >
> >
> > diff --git a/gcc/tree-vect-slp.cc b/gcc/tree-vect-slp.cc
> > index dabd8407aaf..d9961945c1c 100644
> > --- a/gcc/tree-vect-slp.cc
> > +++ b/gcc/tree-vect-slp.cc
> > @@ -3597,14 +3597,24 @@ vect_analyze_slp_instance (vec_info *vinfo,
> > = as_a <loop_vec_info> (vinfo)->reductions;
> > scalar_stmts.create (reductions.length ());
> > for (i = 0; reductions.iterate (i, &next_info); i++)
> > - if ((STMT_VINFO_RELEVANT_P (next_info)
> > - || STMT_VINFO_LIVE_P (next_info))
> > - /* ??? Make sure we didn't skip a conversion around a reduction
> > - path. In that case we'd have to reverse engineer that
> > conversion
> > - stmt following the chain using reduc_idx and from the PHI
> > - using reduc_def. */
> > - && STMT_VINFO_DEF_TYPE (next_info) == vect_reduction_def)
> > - scalar_stmts.quick_push (next_info);
> > + {
> > + gassign *g;
> > + next_info = vect_stmt_to_vectorize (next_info);
> > + if ((STMT_VINFO_RELEVANT_P (next_info)
> > + || STMT_VINFO_LIVE_P (next_info))
> > + /* ??? Make sure we didn't skip a conversion around a
> > reduction
> > + path. In that case we'd have to reverse engineer that
> > + conversion stmt following the chain using reduc_idx and
> > from
> > + the PHI using reduc_def. */
> > + && STMT_VINFO_DEF_TYPE (next_info) == vect_reduction_def
> > + /* Do not discover SLP reductions for lane-reducing ops, that
> > + will fail later. */
> > + && (!(g = dyn_cast <gassign *> (STMT_VINFO_STMT (next_info)))
> > + || (gimple_assign_rhs_code (g) != DOT_PROD_EXPR
> > + && gimple_assign_rhs_code (g) != WIDEN_SUM_EXPR
> > + && gimple_assign_rhs_code (g) != SAD_EXPR)))
> > + scalar_stmts.quick_push (next_info);
> > + }
> > /* If less than two were relevant/live there's nothing to SLP. */
> > if (scalar_stmts.length () < 2)
> > return false;
> > --
> > 2.35.3
