8210387: C2 compilation fails with "assert(node->_last_del == _last) failed: must have deleted the edge just produced"

Refresh iterator and start from the beginning while there is progress when removing dead regions.

Reviewed-by: kvn

src/hotspot/share/opto/phaseX.cpp

@@ -1889,13 +1889,23 @@ Node *PhaseCCP::transform_once( Node *n ) {
       } else if( n->is_Region() ) { // Unreachable region
         // Note: nn == C->top()
         n->set_req(0, NULL);        // Cut selfreference
-        // Eagerly remove dead phis to avoid phis copies creation.
-        for (DUIterator i = n->outs(); n->has_out(i); i++) {
-          Node* m = n->out(i);
-          if( m->is_Phi() ) {
-            assert(type(m) == Type::TOP, "Unreachable region should not have live phis.");
-            replace_node(m, nn);
-            --i; // deleted this phi; rescan starting with next position
+        bool progress = true;
+        uint max = n->outcnt();
+        DUIterator i;
+        while (progress) {
+          progress = false;
+          // Eagerly remove dead phis to avoid phis copies creation.
+          for (i = n->outs(); n->has_out(i); i++) {
+            Node* m = n->out(i);
+            if (m->is_Phi()) {
+              assert(type(m) == Type::TOP, "Unreachable region should not have live phis.");
+              replace_node(m, nn);
+              if (max != n->outcnt()) {
+                progress = true;
+                i = n->refresh_out_pos(i);
+                max = n->outcnt();
+              }
+            }
           }
         }
       }

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

@@ -0,0 +1,63 @@
+/*
+ * Copyright (c) 2018, 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.
+ */
+
+/**
+ * @test
+ * @bug 8210387
+ * @summary Test removal of unreachable regions during CCP.
+ * @library /test/lib
+ * @run main/othervm -Xcomp -XX:-TieredCompilation
+ *                   -XX:CompileOnly=compiler.c2.TestUnreachableRegionDuringCCP::test
+ *                   compiler.c2.TestUnreachableRegionDuringCCP
+ */
+
+package compiler.c2;
+
+import jdk.test.lib.Asserts;
+
+public class TestUnreachableRegionDuringCCP {
+    static int iFld1 = -1;
+    static int iFld2 = -1;
+    static int iArrFld[] = new int[100];
+
+    public static void test() {
+        int i = 1;
+        do {
+            iArrFld[i] = iFld1;
+            iFld1 = 42;
+            for (int j = 1; j < 5; j++) {
+                if (i != 0) {
+                    return; // Always returns
+                }
+                iFld2 += j;
+            }
+        } while (++i < 10);
+    }
+
+    public static void main(String[] args) {
+        test();
+        Asserts.assertEQ(iFld1, 42);
+        Asserts.assertEQ(iFld2, -1);
+        Asserts.assertEQ(iArrFld[1], -1);
+    }
+}