8007898: Incorrect optimization of Memory Barriers in Matcher::post_store_load_barrier()

Summary: generate one "fat" membar instead of set of barriers for volitile store
Reviewed-by: roland

src/share/vm/opto/matcher.cpp

@@ -2305,26 +2305,26 @@ void Matcher::validate_null_checks( ) {
 // atomic instruction acting as a store_load barrier without any
 // intervening volatile load, and thus we don't need a barrier here.
 // We retain the Node to act as a compiler ordering barrier.
-bool Matcher::post_store_load_barrier(const Node *vmb) {
-  Compile *C = Compile::current();
-  assert( vmb->is_MemBar(), "" );
-  assert( vmb->Opcode() != Op_MemBarAcquire, "" );
-  const MemBarNode *mem = (const MemBarNode*)vmb;
-
-  // Get the Proj node, ctrl, that can be used to iterate forward
-  Node *ctrl = NULL;
-  DUIterator_Fast imax, i = mem->fast_outs(imax);
-  while( true ) {
-    ctrl = mem->fast_out(i);            // Throw out-of-bounds if proj not found
-    assert( ctrl->is_Proj(), "only projections here" );
-    ProjNode *proj = (ProjNode*)ctrl;
-    if( proj->_con == TypeFunc::Control &&
-        !C->node_arena()->contains(ctrl) ) // Unmatched old-space only
+bool Matcher::post_store_load_barrier(const Node* vmb) {
+  Compile* C = Compile::current();
+  assert(vmb->is_MemBar(), "");
+  assert(vmb->Opcode() != Op_MemBarAcquire, "");
+  const MemBarNode* membar = vmb->as_MemBar();
+
+  // Get the Ideal Proj node, ctrl, that can be used to iterate forward
+  Node* ctrl = NULL;
+  for (DUIterator_Fast imax, i = membar->fast_outs(imax); i < imax; i++) {
+    Node* p = membar->fast_out(i);
+    assert(p->is_Proj(), "only projections here");
+    if ((p->as_Proj()->_con == TypeFunc::Control) &&
+        !C->node_arena()->contains(p)) { // Unmatched old-space only
+      ctrl = p;
       break;
-    i++;
+    }
   }
+  assert((ctrl != NULL), "missing control projection");
 
-  for( DUIterator_Fast jmax, j = ctrl->fast_outs(jmax); j < jmax; j++ ) {
+  for (DUIterator_Fast jmax, j = ctrl->fast_outs(jmax); j < jmax; j++) {
     Node *x = ctrl->fast_out(j);
     int xop = x->Opcode();
 
@@ -2336,37 +2336,36 @@ bool Matcher::post_store_load_barrier(const Node *vmb) {
     // that a monitor exit operation contains a serializing instruction.
 
     if (xop == Op_MemBarVolatile ||
-        xop == Op_FastLock ||
         xop == Op_CompareAndSwapL ||
         xop == Op_CompareAndSwapP ||
         xop == Op_CompareAndSwapN ||
-        xop == Op_CompareAndSwapI)
+        xop == Op_CompareAndSwapI) {
       return true;
+    }
+
+    // Op_FastLock previously appeared in the Op_* list above.
+    // With biased locking we're no longer guaranteed that a monitor
+    // enter operation contains a serializing instruction.
+    if ((xop == Op_FastLock) && !UseBiasedLocking) {
+      return true;
+    }
 
     if (x->is_MemBar()) {
       // We must retain this membar if there is an upcoming volatile
-      // load, which will be preceded by acquire membar.
-      if (xop == Op_MemBarAcquire)
+      // load, which will be followed by acquire membar.
+      if (xop == Op_MemBarAcquire) {
         return false;
-      // For other kinds of barriers, check by pretending we
-      // are them, and seeing if we can be removed.
-      else
-        return post_store_load_barrier((const MemBarNode*)x);
+      } else {
+        // For other kinds of barriers, check by pretending we
+        // are them, and seeing if we can be removed.
+        return post_store_load_barrier(x->as_MemBar());
+      }
     }
 
-    // Delicate code to detect case of an upcoming fastlock block
-    if( x->is_If() && x->req() > 1 &&
-        !C->node_arena()->contains(x) ) { // Unmatched old-space only
-      Node *iff = x;
-      Node *bol = iff->in(1);
-      // The iff might be some random subclass of If or bol might be Con-Top
-      if (!bol->is_Bool())  return false;
-      assert( bol->req() > 1, "" );
-      return (bol->in(1)->Opcode() == Op_FastUnlock);
-    }
     // probably not necessary to check for these
-    if (x->is_Call() || x->is_SafePoint() || x->is_block_proj())
+    if (x->is_Call() || x->is_SafePoint() || x->is_block_proj()) {
       return false;
+    }
   }
   return false;
 }

src/share/vm/opto/parse3.cpp

@@ -294,25 +294,7 @@ void Parse::do_put_xxx(Node* obj, ciField* field, bool is_field) {
   // If reference is volatile, prevent following volatiles ops from
   // floating up before the volatile write.
   if (is_vol) {
-    // First place the specific membar for THIS volatile index. This first
-    // membar is dependent on the store, keeping any other membars generated
-    // below from floating up past the store.
-    int adr_idx = C->get_alias_index(adr_type);
-    insert_mem_bar_volatile(Op_MemBarVolatile, adr_idx, store);
-
-    // Now place a membar for AliasIdxBot for the unknown yet-to-be-parsed
-    // volatile alias indices. Skip this if the membar is redundant.
-    if (adr_idx != Compile::AliasIdxBot) {
-      insert_mem_bar_volatile(Op_MemBarVolatile, Compile::AliasIdxBot, store);
-    }
-
-    // Finally, place alias-index-specific membars for each volatile index
-    // that isn't the adr_idx membar. Typically there's only 1 or 2.
-    for( int i = Compile::AliasIdxRaw; i < C->num_alias_types(); i++ ) {
-      if (i != adr_idx && C->alias_type(i)->is_volatile()) {
-        insert_mem_bar_volatile(Op_MemBarVolatile, i, store);
-      }
-    }
+    insert_mem_bar(Op_MemBarVolatile); // Use fat membar
   }
 
   // If the field is final, the rules of Java say we are in <init> or <clinit>.

test/compiler/membars/DekkerTest.java

+/*
+ * Copyright 2013 SAP AG.  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 8007898
+ * @summary Incorrect optimization of Memory Barriers in Matcher::post_store_load_barrier().
+ * @run main/othervm -Xbatch -XX:+IgnoreUnrecognizedVMOptions -XX:CICompilerCount=1 -XX:+StressGCM -XX:+StressLCM DekkerTest
+ * @run main/othervm -Xbatch -XX:+IgnoreUnrecognizedVMOptions -XX:CICompilerCount=1 -XX:+StressGCM -XX:+StressLCM DekkerTest
+ * @run main/othervm -Xbatch -XX:+IgnoreUnrecognizedVMOptions -XX:CICompilerCount=1 -XX:+StressGCM -XX:+StressLCM DekkerTest
+ * @author Martin Doerr martin DOT doerr AT sap DOT com
+ *
+ * Run 3 times since the failure is intermittent.
+ */
+
+public class DekkerTest {
+
+    /*
+      Read After Write Test (basically a simple Dekker test with volatile variables)
+      Derived from the original jcstress test, available at:
+        http://hg.openjdk.java.net/code-tools/jcstress/file/6c339a5aa00d/
+        tests-custom/src/main/java/org/openjdk/jcstress/tests/volatiles/DekkerTest.java
+     */
+
+    static final int ITERATIONS = 1000000;
+
+    static class TestData {
+        public volatile int a;
+        public volatile int b;
+    }
+
+    static class ResultData {
+        public int a;
+        public int b;
+    }
+
+    TestData[]   testDataArray;
+    ResultData[] results;
+
+    volatile boolean start;
+
+    public DekkerTest() {
+        testDataArray = new TestData[ITERATIONS];
+        results = new ResultData[ITERATIONS];
+        for (int i = 0; i < ITERATIONS; ++i) {
+            testDataArray[i] = new TestData();
+            results[i] = new ResultData();
+        }
+        start = false;
+    }
+
+    public void reset() {
+        for (int i = 0; i < ITERATIONS; ++i) {
+            testDataArray[i].a = 0;
+            testDataArray[i].b = 0;
+            results[i].a = 0;
+            results[i].b = 0;
+        }
+        start = false;
+    }
+
+    int actor1(TestData t) {
+        t.a = 1;
+        return t.b;
+    }
+
+    int actor2(TestData t) {
+        t.b = 1;
+        return t.a;
+    }
+
+    class Runner1 extends Thread {
+        public void run() {
+            do {} while (!start);
+            for (int i = 0; i < ITERATIONS; ++i) {
+                results[i].a = actor1(testDataArray[i]);
+            }
+        }
+    }
+
+    class Runner2 extends Thread {
+        public void run() {
+            do {} while (!start);
+            for (int i = 0; i < ITERATIONS; ++i) {
+                results[i].b = actor2(testDataArray[i]);
+            }
+        }
+    }
+
+    void testRunner() {
+        Thread thread1 = new Runner1();
+        Thread thread2 = new Runner2();
+        thread1.start();
+        thread2.start();
+        do {} while (!thread1.isAlive());
+        do {} while (!thread2.isAlive());
+        start = true;
+        Thread.yield();
+        try {
+            thread1.join();
+            thread2.join();
+        } catch (InterruptedException e) {
+            System.out.println("interrupted!");
+            System.exit(1);
+        }
+    }
+
+    boolean printResult() {
+        int[] count = new int[4];
+        for (int i = 0; i < ITERATIONS; ++i) {
+            int event_kind = (results[i].a << 1) + results[i].b;
+            ++count[event_kind];
+        }
+        if (count[0] == 0 && count[3] == 0) {
+            System.out.println("[not interesting]");
+            return false; // not interesting
+        }
+        String error = (count[0] == 0) ? " ok" : " disallowed!";
+        System.out.println("[0,0] " + count[0] + error);
+        System.out.println("[0,1] " + count[1]);
+        System.out.println("[1,0] " + count[2]);
+        System.out.println("[1,1] " + count[3]);
+        return (count[0] != 0);
+    }
+
+    public static void main(String args[]) {
+        DekkerTest test = new DekkerTest();
+        final int runs = 30;
+        int failed = 0;
+        for (int c = 0; c < runs; ++c) {
+            test.testRunner();
+            if (test.printResult()) {
+                failed++;
+            }
+            test.reset();
+        }
+        if (failed > 0) {
+            throw new InternalError("FAILED. Got " + failed + " failed ITERATIONS");
+        }
+        System.out.println("PASSED.");
+    }
+
+}