8333876: C2 SuperWord: regression after JDK-8325155: failed: internal connection

Reviewed-by: kvn, roland

Author: eme64

src/hotspot/share/opto/superword.cpp

@@ -2755,11 +2755,11 @@ bool SuperWord::is_vector_use(Node* use, int u_idx) const {
 
   // Reduction: first input is internal connection.
   if (is_marked_reduction(use) && u_idx == 1) {
-#ifdef ASSERT
-      for (uint i = 1; i < u_pk->size(); i++) {
-        assert(u_pk->at(i - 1) == u_pk->at(i)->in(1), "internal connection");
+    for (uint i = 1; i < u_pk->size(); i++) {
+      if (u_pk->at(i - 1) != u_pk->at(i)->in(1)) {
+        return false; // not internally connected
       }
-#endif
+    }
     return true;
   }
 

test/hotspot/jtreg/compiler/loopopts/superword/TestParallelReduction.java

@@ -0,0 +1,60 @@
+/*
+ * Copyright (c) 2024, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package compiler.loopopts.superword;
+
+/*
+ * @test
+ * @bug 8333876
+ * @summary Test parallel reductions.
+ * @run main compiler.loopopts.superword.TestParallelReduction
+ */
+
+public class TestParallelReduction {
+    static int RANGE = 10_000;
+
+    public static void main(String[] args) {
+        float[] a = new float[RANGE];
+        for (int i = 0; i < a.length; i++) {
+            a[i] = i;
+        }
+
+        float gold = test(a);
+
+        for (int i = 0; i < 10_000; i++) {
+            if (test(a) != gold) {
+                throw new RuntimeException("wrong value");
+            }
+        }
+    }
+
+    static float test(float[] a) {
+        float x = 0;
+        float y = 0;
+        for (int i = 0; i < a.length; i+=2) {
+            x += a[i+0];
+            y += a[i+1];
+        }
+        return x+y;
+    }
+}