8250609: C2 crash in IfNode::fold_compares

Reviewed-by: kvn, chagedorn

src/hotspot/share/opto/ifnode.cpp

@@ -993,11 +993,15 @@ bool IfNode::fold_compares_helper(ProjNode* proj, ProjNode* success, ProjNode* f
   }
 
   if (lo && hi) {
+    Node* hook = new Node(1);
+    hook->init_req(0, lo); // Add a use to lo to prevent him from dying
     // Merge the two compares into a single unsigned compare by building (CmpU (n - lo) (hi - lo))
     Node* adjusted_val = igvn->transform(new SubINode(n,  lo));
     if (adjusted_lim == NULL) {
       adjusted_lim = igvn->transform(new SubINode(hi, lo));
     }
+    hook->del_req(0); // Just yank bogus edge
+    hook->destruct();
     Node* newcmp = igvn->transform(new CmpUNode(adjusted_val, adjusted_lim));
     Node* newbool = igvn->transform(new BoolNode(newcmp, cond));
 

test/hotspot/jtreg/compiler/c2/TestFoldCompares.java

@@ -0,0 +1,81 @@
+/*
+ * Copyright (c) 2020, Huawei Technologies Co. Ltd. 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.
+ */
+
+/**
+ * @test
+ * @bug 8250609
+ * @summary C2 crash in IfNode::fold_compares
+ *
+ * @run main/othervm -XX:CompileOnly=compiler.c2.TestFoldCompares::test
+ *                   -XX:-BackgroundCompilation compiler.c2.TestFoldCompares
+ */
+
+package compiler.c2;
+
+public class TestFoldCompares {
+
+    public int test() {
+        byte by = -37;
+        int result = 1;
+        int iArr[] = new int[6];
+
+        for (int i = 0; i < iArr.length; i++) {
+            iArr[i] = 0;
+        }
+
+        for (int i = 16; i < 308; i++) {
+            result *= i;
+            if ((result--) <= (++by)) {
+                continue;
+            }
+
+            for (int j = 3; j < 86; j++) {
+                for (int k = 1; k < 2; k++) {
+                    result >>= 25;
+                }
+
+                for (int k = 1; k < 2; k += 3) {
+                    try {
+                        iArr[k] = (16986 / result);
+                    } catch (ArithmeticException a_e) {
+                    }
+                    result = k;
+                }
+            }
+        }
+
+        return result;
+    }
+
+    public static void main(String[] args) {
+        TestFoldCompares obj = new TestFoldCompares();
+        for (int i = 0; i < 10; i++) {
+            int result = obj.test();
+            if (result != 1) {
+                throw new RuntimeException("Test failed.");
+            }
+        }
+        System.out.println("Test passed.");
+    }
+
+}