1 /*
   2  * Copyright (c) 2012, 2014, 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 jdk.vm.ci.meta;
  24 
  25 /**
  26  * Manages unique deoptimization reasons. Reasons are embedded in compiled code and can be
  27  * invalidated at run time. Subsequent compilations then should not speculate again on such
  28  * invalidated reasons to avoid repeated deoptimization.
  29  *
  30  * All methods of this interface are called by the compiler. There is no need for API to register
  31  * failed speculations during deoptimization, since every VM has different needs there.
  32  */
  33 public interface SpeculationLog {
  34     /**
  35      * Marker interface for speculation objects that can be added to the speculation log.
  36      */
  37     public interface SpeculationReason {
  38     }
  39 
  40     /**
  41      * Marker class that indicates that a speculation has no reason.
  42      */
  43     final class NoSpeculationReason implements SpeculationReason {
  44     }
  45 
  46     class Speculation {
  47         private SpeculationReason reason;
  48 
  49         public Speculation(SpeculationReason reason) {
  50             this.reason = reason;
  51         }
  52 
  53         public SpeculationReason getReason() {
  54             return reason;
  55         }
  56 
  57         @Override
  58         public String toString() {
  59             return reason.toString();
  60         }
  61     }
  62 
  63     Speculation NO_SPECULATION = new Speculation(new NoSpeculationReason());
  64 
  65     /**
  66      * Must be called before compilation, i.e., before a compiler calls {@link #maySpeculate}.
  67      */
  68     void collectFailedSpeculations();
  69 
  70     /**
  71      * If this method returns true, the compiler is allowed to {@link #speculate} with the given
  72      * reason.
  73      */
  74     boolean maySpeculate(SpeculationReason reason);
  75 
  76     /**
  77      * Registers a speculation performed by the compiler. The compiler must guard every call to this
  78      * method for a specific reason with a call to {@link #maySpeculate(SpeculationReason)}.
  79      *
  80      * This API is subject to a benign race where a during the course of a compilation another
  81      * thread might fail a speculation such that {@link #maySpeculate(SpeculationReason)} will
  82      * return false but an earlier call returned true. This method will still return a working
  83      * {@link Speculation} in that case but the compile will eventually be invalidated and the
  84      * compile attempted again without the now invalid speculation.
  85      *
  86      * @param reason an object representing the reason for the speculation
  87      * @return a compiler constant encapsulating the provided reason. It is usually passed as an
  88      *         argument to the deoptimization function.
  89      */
  90     Speculation speculate(SpeculationReason reason);
  91 
  92     /**
  93      * Returns if this log has speculations.
  94      *
  95      * @return true if there are speculations, false otherwise
  96      */
  97     boolean hasSpeculations();
  98 
  99     /**
 100      * Given a {@link JavaConstant} previously returned from
 101      * {@link MetaAccessProvider#encodeSpeculation(Speculation)} return the original
 102      * {@link Speculation} object.
 103      */
 104     Speculation lookupSpeculation(JavaConstant constant);
 105 }