From: Richard Biener <rguenther@suse.de>
Date: Wed, 17 Jul 2024 09:42:13 +0000 (+0200)
Subject: tree-optimization/115959 - ICE with SLP condition reduction
X-Git-Tag: basepoints/gcc-16~7460
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=24689b84b8ec0c74c2b9a72ec4fb467069806bda;p=thirdparty%2Fgcc.git

tree-optimization/115959 - ICE with SLP condition reduction

The following fixes how during reduction epilogue generation we
gather conditional compares for condition reductions, thereby
following the reduction chain via STMT_VINFO_REDUC_IDX.  The issue
is that SLP nodes for COND_EXPRs can have either three or four
children dependent on whether we have legacy GENERIC expressions
in the transitional pattern GIMPLE for the COND_EXPR condition.

	PR tree-optimization/115959
	* tree-vect-loop.cc (vect_create_epilog_for_reduction):
	Get at the REDUC_IDX child in a safer way for COND_EXPR
	nodes.

	* gcc.dg/vect/pr115959.c: New testcase.
---

diff --git a/gcc/testsuite/gcc.dg/vect/pr115959.c b/gcc/testsuite/gcc.dg/vect/pr115959.c
new file mode 100644
index 00000000000..181d5522018
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/pr115959.c
@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+
+int a;
+_Bool *b;
+void f()
+{
+  int t = a;
+  for (int e = 0; e < 2048; e++)
+    {
+      if (!b[e])
+	t = 0;
+    }
+  a = t;
+}
diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
index b8124a32128..a464bc8607c 100644
--- a/gcc/tree-vect-loop.cc
+++ b/gcc/tree-vect-loop.cc
@@ -6090,9 +6090,13 @@ vect_create_epilog_for_reduction (loop_vec_info loop_vinfo,
 		    (std::make_pair (gimple_assign_rhs1 (vec_stmt),
 				     STMT_VINFO_REDUC_IDX (cond_info) == 2));
 		}
-	      /* ???  We probably want to have REDUC_IDX on the SLP node?  */
-	      cond_node = SLP_TREE_CHILDREN
-			    (cond_node)[STMT_VINFO_REDUC_IDX (cond_info)];
+	      /* ???  We probably want to have REDUC_IDX on the SLP node?
+		 We have both three and four children COND_EXPR nodes
+		 dependent on whether the comparison is still embedded
+		 as GENERIC.  So work backwards.  */
+	      int slp_reduc_idx = (SLP_TREE_CHILDREN (cond_node).length () - 3
+				   + STMT_VINFO_REDUC_IDX (cond_info));
+	      cond_node = SLP_TREE_CHILDREN (cond_node)[slp_reduc_idx];
 	    }
 	}
       else