From: Richard Biener <rguenther@suse.de>
Date: Fri, 29 Sep 2023 13:12:54 +0000 (+0200)
Subject: tree-optimization/115254 - don't account single-lane SLP against discovery limit
X-Git-Tag: basepoints/gcc-16~8694
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=eaaa4b88038d4d6eda1b20ab662f1568fd9be31f;p=thirdparty%2Fgcc.git

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 --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,