From b9ec5ebb605936684e95b8dcc12e43ba7d8f2cb4 Mon Sep 17 00:00:00 2001
From: Richard Biener <rguenther@suse.de>
Date: Fri, 11 Jun 2021 13:36:26 +0200
Subject: [PATCH] tree-optimization/101028 - fix endless SLP reassoc discovery

This fixes a missing clearing of mismatched lanes from the
fatal fail path in SLP reassoc discovery in the most conservative
way.

2021-06-11  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/101028
	* tree-vect-slp.c (vect_build_slp_tree_2): When SLP
	reassoc discovery fails fatally, mark appropriate lanes
	in matches[] so.

	* gcc.dg/pr101028.c: New testcase.
---
 gcc/testsuite/gcc.dg/pr101028.c | 34 ++++++++++++++++++++++++++++++++++
 gcc/tree-vect-slp.c             | 26 +++++++++++++++++++++++---
 2 files changed, 57 insertions(+), 3 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/pr101028.c

diff --git a/gcc/testsuite/gcc.dg/pr101028.c b/gcc/testsuite/gcc.dg/pr101028.c
new file mode 100644
index 0000000..501e6af
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr101028.c
@@ -0,0 +1,34 @@
+/* { dg-do compile } */
+/* { dg-options "-Ofast" } */
+
+typedef struct {
+  double x, y;
+} PointInfo;
+
+typedef struct {
+  PointInfo point;
+} PrimitiveInfo;
+
+int TraceBezier_alpha, TraceBezier_i;
+double TraceBezier_weight;
+PointInfo *TraceBezier_points;
+PrimitiveInfo *TraceBezier_primitive_info;
+
+void TracePath() {
+  double *coefficients;
+  PointInfo point;
+  long j;
+  for (; TraceBezier_i; TraceBezier_i++) {
+    point.x = point.y = TraceBezier_alpha = 1.0;
+    j = 0;
+    for (; j < 4; j++) {
+      point.x += TraceBezier_alpha * coefficients[j] *
+                 TraceBezier_primitive_info->point.x;
+      point.y += TraceBezier_alpha * TraceBezier_primitive_info->point.y;
+      TraceBezier_alpha *= TraceBezier_weight;
+      TraceBezier_primitive_info++;
+    }
+    TraceBezier_points[TraceBezier_i] = point;
+    TraceBezier_weight += 1.0;
+  }
+}
diff --git a/gcc/tree-vect-slp.c b/gcc/tree-vect-slp.c
index 897bd6f..9ded585 100644
--- a/gcc/tree-vect-slp.c
+++ b/gcc/tree-vect-slp.c
@@ -1849,14 +1849,28 @@ vect_build_slp_tree_2 (vec_info *vinfo, slp_tree node,
 		 mismatch still hard-FAIL.  */
 	      if (chain_len == 0)
 		hard_fail = false;
+	      else
+		{
+		  matches[lane] = false;
+		  /* ???  We might want to process the other lanes, but
+		     make sure to not give false matching hints to the
+		     caller for lanes we did not process.  */
+		  if (lane != group_size - 1)
+		    matches[0] = false;
+		}
 	      break;
 	    }
 	  else if (chain_len == 0)
 	    chain_len = chain.length ();
 	  else if (chain.length () != chain_len)
-	    /* ???  Here we could slip in magic to compensate with
-	       neutral operands.  */
-	    break;
+	    {
+	      /* ???  Here we could slip in magic to compensate with
+		 neutral operands.  */
+	      matches[lane] = false;
+	      if (lane != group_size - 1)
+		matches[0] = false;
+	      break;
+	    }
 	  chains.quick_push (chain.copy ());
 	  chain.truncate (0);
 	}
@@ -1905,6 +1919,9 @@ vect_build_slp_tree_2 (vec_info *vinfo, slp_tree node,
 		    dump_printf_loc (MSG_NOTE, vect_location,
 				     "giving up on chain due to mismatched "
 				     "def types\n");
+		  matches[lane] = false;
+		  if (lane != group_size - 1)
+		    matches[0] = false;
 		  goto out;
 		}
 	      if (dt == vect_constant_def
@@ -1983,6 +2000,9 @@ vect_build_slp_tree_2 (vec_info *vinfo, slp_tree node,
 			dump_printf_loc (MSG_NOTE, vect_location,
 					 "failed to match up op %d\n", n);
 		      op_stmts.release ();
+		      matches[lane] = false;
+		      if (lane != group_size - 1)
+			matches[0] = false;
 		      goto out;
 		    }
 		  if (dump_enabled_p ())
-- 
2.7.4