Richard Biener <rguent...@suse.de> writes:
> On Wed, 19 Jun 2024, Richard Sandiford wrote:
>
>> Richard Biener <rguent...@suse.de> writes:
>> > We currently fail to re-CSE SLP nodes after optimizing permutes
>> > which results in off cost estimates. For gcc.dg/vect/bb-slp-32.c
>> > this shows in not re-using the SLP node with the load and arithmetic
>> > for both the store and the reduction. The following implements
>> > CSE by re-bst-mapping nodes as finalization part of vect_optimize_slp.
>> >
>> > I've tried to make the CSE part of permute materialization but it
>> > isn't a very good fit there. I've not bothered to implement something
>> > more complete, also handling external defs or defs without
>> > SLP_TREE_SCALAR_STMTS.
>> >
>> > I realize this might result in more BB SLP which in turn might slow
>> > down code given costing for BB SLP is difficult (even that we now
>> > vectorize gcc.dg/vect/bb-slp-32.c on x86_64 might be not a good idea).
>> > This is nevertheless feeding more accurate info to costing which is
>> > good.
>> >
>> > Bootstrapped and tested on x86_64-unknown-linux-gnu.
>> >
>> > Does this look OK?
>> >
>> > Thanks,
>> > Richard.
>> >
>> > PR tree-optimization/114413
>> > * tree-vect-slp.cc (release_scalar_stmts_to_slp_tree_map):
>> > New function, split out from ...
>> > (vect_analyze_slp): ... here. Call it.
>> > (vect_cse_slp_nodes): New function.
>> > (vect_optimize_slp): Call it.
>> >
>> > * gcc.dg/vect/bb-slp-32.c: Expect CSE and vectorization on x86.
>> > ---
>> > gcc/testsuite/gcc.dg/vect/bb-slp-32.c | 6 +++
>> > gcc/tree-vect-slp.cc | 77 ++++++++++++++++++++++-----
>> > 2 files changed, 71 insertions(+), 12 deletions(-)
>> >
>> > diff --git a/gcc/testsuite/gcc.dg/vect/bb-slp-32.c
>> > b/gcc/testsuite/gcc.dg/vect/bb-slp-32.c
>> > index 4f72727b694..475b241c36e 100644
>> > --- a/gcc/testsuite/gcc.dg/vect/bb-slp-32.c
>> > +++ b/gcc/testsuite/gcc.dg/vect/bb-slp-32.c
>> > @@ -38,3 +38,9 @@ int main()
>> > abort ();
>> > return 0;
>> > }
>> > +
>> > +/* This is a weak test but we want to re-use the arithmetic for both the
>> > + store and the reduction. */
>> > +/* { dg-final { scan-tree-dump "re-using SLP tree" "slp2" { target {
>> > x86_64-*-* i?86-*-* } } } } */
>> > +/* On i386 we vectorize both the store and the reduction. */
>> > +/* { dg-final { scan-tree-dump-times "basic block part vectorized" 2
>> > "slp2" { target { x86_64-*-* i?86-*-* } } } } */
>> > diff --git a/gcc/tree-vect-slp.cc b/gcc/tree-vect-slp.cc
>> > index 2552dacbd69..980d1e7267d 100644
>> > --- a/gcc/tree-vect-slp.cc
>> > +++ b/gcc/tree-vect-slp.cc
>> > @@ -1586,6 +1586,23 @@ bst_traits::equal (value_type existing, value_type
>> > candidate)
>> > return true;
>> > }
>> >
>> > +typedef hash_map <vec <stmt_vec_info>, slp_tree,
>> > + simple_hashmap_traits <bst_traits, slp_tree> >
>> > + scalar_stmts_to_slp_tree_map_t;
>> > +
>> > +/* Release BST_MAP. */
>> > +
>> > +static void
>> > +release_scalar_stmts_to_slp_tree_map (scalar_stmts_to_slp_tree_map_t
>> > *bst_map)
>> > +{
>> > + /* The map keeps a reference on SLP nodes built, release that. */
>> > + for (scalar_stmts_to_slp_tree_map_t::iterator it = bst_map->begin ();
>> > + it != bst_map->end (); ++it)
>> > + if ((*it).second)
>> > + vect_free_slp_tree ((*it).second);
>> > + delete bst_map;
>> > +}
>> > +
>> > /* ??? This was std::pair<std::pair<tree_code, vect_def_type>, tree>
>> > but then vec::insert does memmove and that's not compatible with
>> > std::pair. */
>> > @@ -1684,10 +1701,6 @@ vect_slp_linearize_chain (vec_info *vinfo,
>> > }
>> > }
>> >
>> > -typedef hash_map <vec <stmt_vec_info>, slp_tree,
>> > - simple_hashmap_traits <bst_traits, slp_tree> >
>> > - scalar_stmts_to_slp_tree_map_t;
>> > -
>> > static slp_tree
>> > vect_build_slp_tree_2 (vec_info *vinfo, slp_tree node,
>> > vec<stmt_vec_info> stmts, unsigned int group_size,
>> > @@ -4308,14 +4321,7 @@ vect_analyze_slp (vec_info *vinfo, unsigned
>> > max_tree_size)
>> > }
>> > }
>> >
>> > -
>> > -
>> > - /* The map keeps a reference on SLP nodes built, release that. */
>> > - for (scalar_stmts_to_slp_tree_map_t::iterator it = bst_map->begin ();
>> > - it != bst_map->end (); ++it)
>> > - if ((*it).second)
>> > - vect_free_slp_tree ((*it).second);
>> > - delete bst_map;
>> > + release_scalar_stmts_to_slp_tree_map (bst_map);
>> >
>> > if (pattern_found && dump_enabled_p ())
>> > {
>> > @@ -6373,6 +6379,43 @@ vect_optimize_slp_pass::run ()
>> > free_graph (m_slpg);
>> > }
>> >
>> > +/* Apply CSE to NODE and its children using BST_MAP. */
>> > +
>> > +static void
>> > +vect_cse_slp_nodes (scalar_stmts_to_slp_tree_map_t *bst_map, slp_tree&
>> > node)
>> > +{
>> > + if (SLP_TREE_DEF_TYPE (node) == vect_internal_def
>> > + && SLP_TREE_CODE (node) != VEC_PERM_EXPR
>> > + /* Besides some VEC_PERM_EXPR, two-operator nodes also
>> > + lack scalar stmts and thus CSE doesn't work via bst_map. Ideally
>> > + we'd have sth that works for all internal and external nodes. */
>> > + && !SLP_TREE_SCALAR_STMTS (node).is_empty ())
>> > + {
>> > + if (slp_tree *leader = bst_map->get (SLP_TREE_SCALAR_STMTS (node)))
>> > + {
>> > + if (*leader != node)
>> > + {
>> > + if (dump_enabled_p ())
>> > + dump_printf_loc (MSG_NOTE, vect_location,
>> > + "re-using SLP tree %p for %p\n",
>> > + (void *)*leader, (void *)node);
>> > + vect_free_slp_tree (node);
>> > + (*leader)->refcnt += 1;
>> > + node = *leader;
>> > + }
>> > + return;
>> > + }
>> > +
>> > + bst_map->put (SLP_TREE_SCALAR_STMTS (node).copy (), node);
>> > + node->refcnt += 1;
>>
>> Since we're not starting with zeroed refcnts, won't this end up double
>> counting the references?
>
> This is for the reference bst_map holds, we're releasing that when
> destroying bst_map. I copied this from other bst-map populating
> code (and release_scalar_stmts_to_slp_tree_map performs the
> corresponding decrement).
Ah, ok, thanks!
