[gcc r15-859] tree-optimization/115254 - don't account single-lane SLP against discovery limit

[Richard Biener via Gcc-cvs]

https://gcc.gnu.org/g:eaaa4b88038d4d6eda1b20ab662f1568fd9be31f

commit r15-859-geaaa4b88038d4d6eda1b20ab662f1568fd9be31f
Author: Richard Biener <rguent...@suse.de>
Date:   Fri Sep 29 15:12:54 2023 +0200

    tree-optimization/115254 - don't account single-lane SLP against discovery 
limit
    
    The following avoids accounting single-lane SLP to the discovery
    limit.  As the two testcases show this makes discovery fail,
    unfortunately even not the same across targets.  The following
    should fix two FAILs for GCN as a side-effect.
    
            PR tree-optimization/115254
            * tree-vect-slp.cc (vect_build_slp_tree): Only account
            multi-lane SLP to limit.
    
            * gcc.dg/vect/slp-cond-2-big-array.c: Expect 4 times SLP.
            * gcc.dg/vect/slp-cond-2.c: Likewise.

Diff:
---
 gcc/testsuite/gcc.dg/vect/slp-cond-2-big-array.c |  2 +-
 gcc/testsuite/gcc.dg/vect/slp-cond-2.c           |  2 +-
 gcc/tree-vect-slp.cc                             | 31 ++++++++++++++----------
 3 files changed, 20 insertions(+), 15 deletions(-)

diff --git a/gcc/testsuite/gcc.dg/vect/slp-cond-2-big-array.c 
b/gcc/testsuite/gcc.dg/vect/slp-cond-2-big-array.c
index cb7eb94b3a3..9a9f63c0b8d 100644
--- a/gcc/testsuite/gcc.dg/vect/slp-cond-2-big-array.c
+++ b/gcc/testsuite/gcc.dg/vect/slp-cond-2-big-array.c
@@ -128,4 +128,4 @@ main ()
   return 0;
 }
 
-/* { dg-final { scan-tree-dump-times "vectorizing stmts using SLP" 3 "vect" } 
} */
+/* { dg-final { scan-tree-dump-times "vectorizing stmts using SLP" 4 "vect" } 
} */
diff --git a/gcc/testsuite/gcc.dg/vect/slp-cond-2.c 
b/gcc/testsuite/gcc.dg/vect/slp-cond-2.c
index 1dcee46cd95..08bbb3dbec6 100644
--- a/gcc/testsuite/gcc.dg/vect/slp-cond-2.c
+++ b/gcc/testsuite/gcc.dg/vect/slp-cond-2.c
@@ -128,4 +128,4 @@ main ()
   return 0;
 }
 
-/* { dg-final { scan-tree-dump-times "vectorizing stmts using SLP" 3 "vect" } 
} */
+/* { dg-final { scan-tree-dump-times "vectorizing stmts using SLP" 4 "vect" } 
} */
diff --git a/gcc/tree-vect-slp.cc b/gcc/tree-vect-slp.cc
index c7ed520b629..7a963e28063 100644
--- a/gcc/tree-vect-slp.cc
+++ b/gcc/tree-vect-slp.cc
@@ -1725,21 +1725,26 @@ vect_build_slp_tree (vec_info *vinfo,
   SLP_TREE_SCALAR_STMTS (res) = stmts;
   bst_map->put (stmts.copy (), res);
 
-  if (*limit == 0)
+  /* Single-lane SLP doesn't have the chance of run-away, do not account
+     it to the limit.  */
+  if (stmts.length () > 1)
     {
-      if (dump_enabled_p ())
-       dump_printf_loc (MSG_NOTE, vect_location,
-                        "SLP discovery limit exceeded\n");
-      /* Mark the node invalid so we can detect those when still in use
-        as backedge destinations.  */
-      SLP_TREE_SCALAR_STMTS (res) = vNULL;
-      SLP_TREE_DEF_TYPE (res) = vect_uninitialized_def;
-      res->failed = XNEWVEC (bool, group_size);
-      memset (res->failed, 0, sizeof (bool) * group_size);
-      memset (matches, 0, sizeof (bool) * group_size);
-      return NULL;
+      if (*limit == 0)
+       {
+         if (dump_enabled_p ())
+           dump_printf_loc (MSG_NOTE, vect_location,
+                            "SLP discovery limit exceeded\n");
+         /* Mark the node invalid so we can detect those when still in use
+            as backedge destinations.  */
+         SLP_TREE_SCALAR_STMTS (res) = vNULL;
+         SLP_TREE_DEF_TYPE (res) = vect_uninitialized_def;
+         res->failed = XNEWVEC (bool, group_size);
+         memset (res->failed, 0, sizeof (bool) * group_size);
+         memset (matches, 0, sizeof (bool) * group_size);
+         return NULL;
+       }
+      --*limit;
     }
-  --*limit;
 
   if (dump_enabled_p ())
     dump_printf_loc (MSG_NOTE, vect_location,