8327172: C2 SuperWord: data node in loop has no input in loop: replace assert with bailout

Reviewed-by: chagedorn, kvn

Author: eme64

src/hotspot/share/opto/superword.cpp

@@ -2957,7 +2957,6 @@ VStatus VLoopBody::construct() {
         return VStatus::make_failure(VLoopBody::FAILURE_NODE_NOT_ALLOWED);
       }
 
-#ifdef ASSERT
       if (!n->is_CFG()) {
         bool found = false;
         for (uint j = 0; j < n->req(); j++) {
@@ -2967,9 +2966,17 @@ VStatus VLoopBody::construct() {
             break;
           }
         }
-        assert(found, "every non-cfg node must have an input that is also inside the loop");
-      }
+        if (!found) {
+          // If all inputs to a data-node are outside the loop, the node itself should be outside the loop.
+#ifndef PRODUCT
+          if (_vloop.is_trace_body()) {
+            tty->print_cr("VLoopBody::construct: fails because data node in loop has no input in loop:");
+            n->dump();
+          }
 #endif
+          return VStatus::make_failure(VLoopBody::FAILURE_UNEXPECTED_CTRL);
+        }
+      }
     }
   }
 

src/hotspot/share/opto/vectorization.hpp

@@ -324,6 +324,7 @@ class VLoopMemorySlices : public StackObj {
 class VLoopBody : public StackObj {
 private:
   static constexpr char const* FAILURE_NODE_NOT_ALLOWED = "encontered unhandled node";
+  static constexpr char const* FAILURE_UNEXPECTED_CTRL  = "data node in loop has no input in loop";
 
   const VLoop& _vloop;
 

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

@@ -0,0 +1,91 @@
+/*
+ * 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 id=Vanilla
+ * @bug 8327172
+ * @summary Test bad loop ctrl: a node is in the loop, but has no input in the loop
+ * @run main/othervm compiler.loopopts.superword.TestNoInputInLoop
+ */
+
+/*
+ * @test id=WithFlags
+ * @bug 8327172
+ * @summary Test bad loop ctrl: a node is in the loop, but has no input in the loop
+ * @run main/othervm -Xbatch -XX:PerMethodTrapLimit=0
+ *                   compiler.loopopts.superword.TestNoInputInLoop
+ */
+
+/*
+ * @test id=WithMoreFlags
+ * @bug 8327172
+ * @summary Test bad loop ctrl: a node is in the loop, but has no input in the loop
+ * @run main/othervm -Xbatch -XX:PerMethodTrapLimit=0
+ *                   -XX:CompileCommand=compileonly,compiler.loopopts.superword.TestNoInputInLoop::test*
+ *                   compiler.loopopts.superword.TestNoInputInLoop
+ */
+
+public class TestNoInputInLoop {
+    static long lFld;
+    static float fFld;
+    static int iArr[] = new int[400];
+
+    public static void main(String[] strArr) {
+        for (int i = 0; i < 100; i++) {
+            test1();
+        }
+        for (int i = 0; i < 1_000; i++) {
+            test2(0);
+        }
+    }
+
+    // It specifically reproduced with UseAVX=2
+    // 1. PhaseIdealLoop::build_loop_early
+    //    We have a Store in a loop, with a Load after it.
+    //    Both have ctrl as the CountedLoopNode.
+    // 2. split_if_with_blocks -> PhaseIdealLoop::try_move_store_before_loop
+    //    The Store is moved out of the loop, and its ctrl updated accordingly.
+    //    But the Load has its ctrl not updated, even though it has now no input in the loop.
+    // 3. SuperWord (VLoopBody::construct)
+    //    We detect a data node in the loop that has no input in the loop.
+    //    This is not expected.
+
+    // OSR failure
+    static void test1() {
+        for (int i = 0; i < 200; i++) {
+            fFld *= iArr[0] - lFld;
+            iArr[1] = (int) lFld;
+            for (int j = 0; j < 100_000; j++) {} // empty loop, trigger OSR
+        }
+    }
+
+    // Normal compilation
+    static void test2(int start) {
+        for (int i = start; i < 200; i++) {
+            fFld *= iArr[0] - lFld;
+            iArr[1] = (int) lFld;
+        }
+    }
+}