1 /*
   2  * Copyright (c) 2011, 2016, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  */
  23 package org.graalvm.compiler.core.common;
  24 
  25 // JaCoCo Exclude
  26 
  27 /**
  28  * Marker interface for location identities. A different location identity of two memory accesses
  29  * guarantees that the two accesses do not interfere.
  30  *
  31  * Clients of {@link LocationIdentity} must use {@link #equals(Object)}, not {@code ==}, when
  32  * comparing two {@link LocationIdentity} values for equality. Likewise, they must not use
  33  * {@link java.util.IdentityHashMap}s with {@link LocationIdentity} values as keys.
  34  */
  35 public abstract class LocationIdentity {
  36 
  37     private static final class AnyLocationIdentity extends LocationIdentity {
  38         @Override
  39         public boolean isImmutable() {
  40             return false;
  41         }
  42 
  43         @Override
  44         public String toString() {
  45             return "ANY_LOCATION";
  46         }
  47     }
  48 
  49     private static final class InitLocationIdentity extends LocationIdentity {
  50         @Override
  51         public boolean isImmutable() {
  52             return true;
  53         }
  54 
  55         @Override
  56         public String toString() {
  57             return "INIT_LOCATION";
  58         }
  59     }
  60 
  61     public static final LocationIdentity ANY_LOCATION = new AnyLocationIdentity();
  62     public static final LocationIdentity INIT_LOCATION = new InitLocationIdentity();
  63 
  64     /**
  65      * Indicates that the given location is the union of all possible mutable locations. A write to
  66      * such a location kill all reads from mutable locations and a read from this location is killed
  67      * by any write (except for initialization writes).
  68      */
  69     public static LocationIdentity any() {
  70         return ANY_LOCATION;
  71     }
  72 
  73     /**
  74      * Location only allowed to be used for writes. Indicates that a completely new memory location
  75      * is written. Kills no read. The previous value at the given location must be either
  76      * uninitialized or null. Writes to this location do not need a GC pre-barrier.
  77      */
  78     public static LocationIdentity init() {
  79         return INIT_LOCATION;
  80     }
  81 
  82     /**
  83      * Denotes a location is unchanging in all cases. Not that this is different than the Java
  84      * notion of final which only requires definite assignment.
  85      */
  86     public abstract boolean isImmutable();
  87 
  88     public final boolean isMutable() {
  89         return !isImmutable();
  90     }
  91 
  92     public final boolean isAny() {
  93         return this == ANY_LOCATION;
  94     }
  95 
  96     public final boolean isInit() {
  97         return this == INIT_LOCATION;
  98     }
  99 
 100     public final boolean isSingle() {
 101         return this != ANY_LOCATION;
 102     }
 103 
 104     public final boolean overlaps(LocationIdentity other) {
 105         return isAny() || other.isAny() || this.equals(other);
 106     }
 107 }