8274145: C2: condition incorrectly made redundant with dominating main loop exit condition

Reviewed-by: kvn, neliasso

src/hotspot/share/opto/loopnode.hpp

@@ -1632,6 +1632,8 @@ public:
   Node* compute_early_ctrl(Node* n, Node* n_ctrl);
 
   void try_sink_out_of_loop(Node* n);
+
+  bool safe_for_if_replacement(const Node* dom) const;
 };
 
 

src/hotspot/share/opto/loopopts.cpp

@@ -1392,7 +1392,8 @@ void PhaseIdealLoop::split_if_with_blocks_post(Node *n) {
       Node *prevdom = n;
       Node *dom = idom(prevdom);
       while (dom != cutoff) {
-        if (dom->req() > 1 && dom->in(1) == bol && prevdom->in(0) == dom) {
+        if (dom->req() > 1 && dom->in(1) == bol && prevdom->in(0) == dom &&
+            safe_for_if_replacement(dom)) {
           // It's invalid to move control dependent data nodes in the inner
           // strip-mined loop, because:
           //  1) break validation of LoopNode::verify_strip_mined()
@@ -1430,6 +1431,25 @@ void PhaseIdealLoop::split_if_with_blocks_post(Node *n) {
   }
 }
 
+bool PhaseIdealLoop::safe_for_if_replacement(const Node* dom) const {
+  if (!dom->is_CountedLoopEnd()) {
+    return true;
+  }
+  CountedLoopEndNode* le = dom->as_CountedLoopEnd();
+  CountedLoopNode* cl = le->loopnode();
+  if (cl == NULL) {
+    return true;
+  }
+  if (!cl->is_main_loop()) {
+    return true;
+  }
+  if (cl->is_canonical_loop_entry() == NULL) {
+    return true;
+  }
+  // Further unrolling is possible so loop exit condition might change
+  return false;
+}
+
 // See if a shared loop-varying computation has no loop-varying uses.
 // Happens if something is only used for JVM state in uncommon trap exits,
 // like various versions of induction variable+offset.  Clone the

test/hotspot/jtreg/compiler/loopopts/TestIfReplacedByMainLoopExit.java

@@ -0,0 +1,126 @@
+/*
+ * Copyright (c) 2021, Red Hat, Inc. 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 8274145
+ * @summary C2: Incorrect computation after JDK-8269752
+ *
+ * @run main/othervm -Xcomp -XX:CompileOnly=TestIfReplacedByMainLoopExit::iMeth -XX:CompileOnly=TestIfReplacedByMainLoopExit::mainTest -XX:-TieredCompilation TestIfReplacedByMainLoopExit
+ *
+ */
+
+public class TestIfReplacedByMainLoopExit {
+
+    public static final int N = 400;
+
+    public static long instanceCount=3024694135L;
+    public static boolean bFld=true;
+    public int iFld=-11;
+
+    public static long iMeth_check_sum = 0;
+
+    public static void vMeth(int i3, int i4, int i5) {
+
+        int i6=-71, i7=88, i8=217, i9=14, i10=9677, i18=-244, i19=107, iArr[]=new int[N];
+    }
+
+    public static void init(int[] a, int seed) {
+        for (int j = 0; j < a.length; j++) {
+            a[j] = (j % 2 == 0) ? seed + j : seed - j;
+        }
+    }
+
+    public static long checkSum(int[] a) {
+        long sum = 0;
+        for (int j = 0; j < a.length; j++) {
+            sum += (a[j] / (j + 1) + a[j] % (j + 1));
+        }
+        return sum;
+    }
+
+    public static int iMeth(boolean b, int i2) {
+
+        byte by=81;
+        int i21=-24074, i22=7, i23=-7, i24=-70, iArr2[]=new int[N];
+        boolean b2=false;
+        init(iArr2, -27);
+
+        vMeth(189, i2, i2);
+        for (int i20 : iArr2) {
+            by *= (byte) TestIfReplacedByMainLoopExit.instanceCount;
+            for (i23 = 1; i23 < 4; ++i23) {
+                i24 -= i23;
+                TestIfReplacedByMainLoopExit.bFld = b2;
+            }
+        }
+        long meth_res = (b ? 1 : 0) + i2 + by + i21 + i22 + i23 + i24 + (b2 ? 1 : 0) + checkSum(iArr2);
+        iMeth_check_sum += meth_res;
+        return (int)meth_res;
+    }
+
+    public void mainTest(String[] strArr1) {
+        int i, i1, i25, i26=9, i27, i28;
+        byte by1=35;
+        float f2;
+
+        for (i = 17; 310 > i; ++i) {
+            i1 = ((iMeth(TestIfReplacedByMainLoopExit.bFld, iFld) - iFld) + by1);
+        }
+        i1 = 231;
+        iFld += -13496;
+        for (i25 = 2; i25 < 271; i25++) {
+            i26 -= i;
+            if (TestIfReplacedByMainLoopExit.bFld) break;
+        }
+        i26 = i;
+        iFld += (int)1.338F;
+        iFld += 30984;
+        i27 = 1;
+        do {
+            iFld *= i25;
+            for (i28 = 4; i28 < 75; ++i28) {
+                i1 += i25;
+            }
+        } while (++i27 < 335);
+        f2 = 210;
+        do {
+            iFld -= i25;
+        } while (--f2 > 0);
+
+        System.out.println("iFld = " + iFld);
+    }
+
+    public static void main(String[] strArr) {
+        TestIfReplacedByMainLoopExit _instance = new TestIfReplacedByMainLoopExit();
+        _instance.mainTest(strArr);
+        int iFld_sav = _instance.iFld;
+        for (int i = 0; i < 10; i++ ) {
+            _instance.iFld=-11;
+            _instance.mainTest(strArr);
+            if (_instance.iFld != iFld_sav) {
+                throw new RuntimeException("incorrect execution " + _instance.iFld + " != " + iFld_sav);
+            }
+        }
+    }
+}