src/jdk.internal.vm.compiler/share/classes/org.graalvm.compiler.loop.phases/src/org/graalvm/compiler/loop/phases/LoopSafepointEliminationPhase.java

rev 56282 : [mq]: graal

@@ -1,7 +1,7 @@
 /*
- * Copyright (c) 2011, 2018, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2011, 2019, 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.

@@ -38,23 +38,29 @@
 public class LoopSafepointEliminationPhase extends BasePhase<MidTierContext> {
 
     @Override
     protected void run(StructuredGraph graph, MidTierContext context) {
         LoopsData loops = new LoopsData(graph);
-        if (context.getOptimisticOptimizations().useLoopLimitChecks(graph.getOptions()) && graph.getGuardsStage().allowsFloatingGuards()) {
             loops.detectedCountedLoops();
             for (LoopEx loop : loops.countedLoops()) {
                 if (loop.loop().getChildren().isEmpty() && loop.counted().getStamp().getBits() <= 32) {
                     boolean hasSafepoint = false;
                     for (LoopEndNode loopEnd : loop.loopBegin().loopEnds()) {
                         hasSafepoint |= loopEnd.canSafepoint();
                     }
                     if (hasSafepoint) {
+                    if (!loop.counted().counterNeverOverflows()) {
+                        // Counter can overflow, need to create a guard.
+                        if (context.getOptimisticOptimizations().useLoopLimitChecks(graph.getOptions()) && graph.getGuardsStage().allowsFloatingGuards()) {
                         loop.counted().createOverFlowGuard();
-                        loop.loopBegin().disableSafepoint();
+                        } else {
+                            // Cannot disable this safepoint, because the loop could overflow.
+                            continue;
                     }
                 }
+                    loop.loopBegin().disableSafepoint();
+                }
             }
         }
         for (LoopEx loop : loops.loops()) {
             for (LoopEndNode loopEnd : loop.loopBegin().loopEnds()) {
                 Block b = loops.getCFG().blockFor(loopEnd);