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test/compiler/loopopts/TestLoopPeeling.java

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@@ -1,7 +1,7 @@
 /*
- * Copyright (c) 2016, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2017, 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.

@@ -21,29 +21,37 @@
  * questions.
  */
 
 /*
  * @test
- * @bug 8078262
+ * @bug 8078262 8177095
  * @summary Tests correct dominator information after loop peeling.
- * @run main/othervm -Xcomp -XX:CompileCommand=compileonly,TestLoopPeeling::test* TestLoopPeeling
+ *
+ * @run main/othervm -Xcomp
+ *      -XX:CompileCommand=compileonly,compiler.loopopts.TestLoopPeeling::test*
+ *      compiler.loopopts.TestLoopPeeling
  */
+
+package compiler.loopopts;
+
 public class TestLoopPeeling {
 
     public int[] array = new int[100];
 
     public static void main(String args[]) {
         TestLoopPeeling test = new TestLoopPeeling();
         try {
-            test.testArrayAccess(0, 1);
+            test.testArrayAccess1(0, 1);
+            test.testArrayAccess2(0);
+            test.testArrayAccess3(0, false);
             test.testArrayAllocation(0, 1);
         } catch (Exception e) {
             // Ignore exceptions
         }
     }
 
-    public void testArrayAccess(int index, int inc) {
+    public void testArrayAccess1(int index, int inc) {
         int storeIndex = -1;
 
         for (; index < 10; index += inc) {
             // This loop invariant check triggers loop peeling because it can
             // be moved out of the loop (see 'IdealLoopTree::policy_peeling').

@@ -55,11 +63,11 @@
             // address computation (see 'PhaseIdealLoop::split_if_with_blocks_post').
             if (storeIndex > 0 && array[storeIndex] == 42) return;
 
             if (index == 42) {
                 // This store and the corresponding range check are moved out of the
-                // loop and both used after old loop and the peeled iteration exit.
+                // loop and both used after main loop and the peeled iteration exit.
                 // For the peeled iteration, storeIndex is always -1 and the ConvI2L
                 // is replaced by TOP. However, the range check is not folded because
                 // we don't do the split if optimization in PhaseIdealLoop2.
                 // As a result, we have a (dead) control path from the peeled iteration
                 // to the StoreI but the data path is removed.

@@ -69,10 +77,48 @@
 
             storeIndex++;
         }
     }
 
+    public int testArrayAccess2(int index) {
+        // Load1 and the corresponding range check are moved out of the loop
+        // and both are used after the main loop and the peeled iteration exit.
+        // For the peeled iteration, storeIndex is always Integer.MIN_VALUE and
+        // for the main loop it is 0. Hence, the merging phi has type int:<=0.
+        // Load1 reads the array at index ConvI2L(CastII(AddI(storeIndex, -1)))
+        // where the CastII is range check dependent and has type int:>=0.
+        // The CastII gets pushed through the AddI and its type is changed to int:>=1
+        // which does not overlap with the input type of storeIndex (int:<=0).
+        // The CastII is replaced by TOP causing a cascade of other eliminations.
+        // Since the control path through the range check CmpU(AddI(storeIndex, -1))
+        // is not eliminated, the graph is in a corrupted state. We fail once we merge
+        // with the result of Load2 because we get data from a non-dominating region.
+        int storeIndex = Integer.MIN_VALUE;
+        for (; index < 10; ++index) {
+            if (index == 42) {
+                return array[storeIndex-1]; // Load1
+            }
+            storeIndex = 0;
+        }
+        return array[42]; // Load2
+    }
+
+    public int testArrayAccess3(int index, boolean b) {
+        // Same as testArrayAccess2 but manifests as crash in register allocator.
+        int storeIndex = Integer.MIN_VALUE;
+        for (; index < 10; ++index) {
+            if (b) {
+                return 0;
+            }
+            if (index == 42) {
+                return array[storeIndex-1]; // Load1
+            }
+            storeIndex = 0;
+        }
+        return array[42]; // Load2
+    }
+
     public byte[] testArrayAllocation(int index, int inc) {
         int allocationCount = -1;
         byte[] result;
 
         for (; index < 10; index += inc) {

@@ -80,11 +126,11 @@
             // be moved out of the loop (see 'IdealLoopTree::policy_peeling').
             if (inc == 42) return null;
 
             if (index == 42) {
                 // This allocation and the corresponding size check are moved out of the
-                // loop and both used after old loop and the peeled iteration exit.
+                // loop and both used after main loop and the peeled iteration exit.
                 // For the peeled iteration, allocationCount is always -1 and the ConvI2L
                 // is replaced by TOP. However, the size check is not folded because
                 // we don't do the split if optimization in PhaseIdealLoop2.
                 // As a result, we have a (dead) control path from the peeled iteration
                 // to the allocation but the data path is removed.
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