Mercurial > hg > graal-compiler
view graal/com.oracle.max.cri/src/com/oracle/max/cri/util/MemoryBarriers.java @ 4205:2af849af1723
moved graphbuilder into the graal.java project.
author | Thomas Wuerthinger <thomas.wuerthinger@oracle.com> |
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date | Tue, 03 Jan 2012 18:22:10 +0100 |
parents | 8c9c0e1eaab1 |
children |
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/* * Copyright (c) 2011, 2011, 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. * * 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. */ package com.oracle.max.cri.util; /** * Constants and intrinsic definition for memory barriers. * * The documentation for each constant is taken from Doug Lea's * <a href="http://gee.cs.oswego.edu/dl/jmm/cookbook.html">The JSR-133 Cookbook for Compiler Writers</a>. * <p> * The {@code JMM_*} constants capture the memory barriers necessary to implement the Java Memory Model * with respect to volatile field accesses. Their values are explained by this * comment from templateTable_i486.cpp in the HotSpot source code: * <pre> * Volatile variables demand their effects be made known to all CPU's in * order. Store buffers on most chips allow reads & writes to reorder; the * JMM's ReadAfterWrite.java test fails in -Xint mode without some kind of * memory barrier (i.e., it's not sufficient that the interpreter does not * reorder volatile references, the hardware also must not reorder them). * * According to the new Java Memory Model (JMM): * (1) All volatiles are serialized wrt to each other. * ALSO reads & writes act as acquire & release, so: * (2) A read cannot let unrelated NON-volatile memory refs that happen after * the read float up to before the read. It's OK for non-volatile memory refs * that happen before the volatile read to float down below it. * (3) Similarly, a volatile write cannot let unrelated NON-volatile memory refs * that happen BEFORE the write float down to after the write. It's OK for * non-volatile memory refs that happen after the volatile write to float up * before it. * * We only put in barriers around volatile refs (they are expensive), not * _between_ memory refs (which would require us to track the flavor of the * previous memory refs). Requirements (2) and (3) require some barriers * before volatile stores and after volatile loads. These nearly cover * requirement (1) but miss the volatile-store-volatile-load case. This final * case is placed after volatile-stores although it could just as well go * before volatile-loads. * </pre> */ public class MemoryBarriers { /** * The sequence {@code Load1; LoadLoad; Load2} ensures that {@code Load1}'s data are loaded before data accessed * by {@code Load2} and all subsequent load instructions are loaded. In general, explicit {@code LoadLoad} * barriers are needed on processors that perform speculative loads and/or out-of-order processing in which * waiting load instructions can bypass waiting stores. On processors that guarantee to always preserve load * ordering, these barriers amount to no-ops. */ public static final int LOAD_LOAD = 0x0001; /** * The sequence {@code Load1; LoadStore; Store2} ensures that {@code Load1}'s data are loaded before all data * associated with {@code Store2} and subsequent store instructions are flushed. {@code LoadStore} barriers are * needed only on those out-of-order processors in which waiting store instructions can bypass loads. */ public static final int LOAD_STORE = 0x0002; /** * The sequence {@code Store1; StoreLoad; Load2} ensures that {@code Store1}'s data are made visible to other * processors (i.e., flushed to main memory) before data accessed by {@code Load2} and all subsequent load * instructions are loaded. {@code StoreLoad} barriers protect against a subsequent load incorrectly using * {@code Store1}'s data value rather than that from a more recent store to the same location performed by a * different processor. Because of this, on the processors discussed below, a {@code StoreLoad} is strictly * necessary only for separating stores from subsequent loads of the same location(s) as were stored before the * barrier. {@code StoreLoad} barriers are needed on nearly all recent multiprocessors, and are usually the most * expensive kind. Part of the reason they are expensive is that they must disable mechanisms that ordinarily * bypass cache to satisfy loads from write-buffers. This might be implemented by letting the buffer fully * flush, among other possible stalls. */ public static final int STORE_LOAD = 0x0004; /** * The sequence {@code Store1; StoreStore; Store2} ensures that {@code Store1}'s data are visible to other * processors (i.e., flushed to memory) before the data associated with {@code Store2} and all subsequent store * instructions. In general, {@code StoreStore} barriers are needed on processors that do not otherwise * guarantee strict ordering of flushes from write buffers and/or caches to other processors or main memory. */ public static final int STORE_STORE = 0x0008; public static final int JMM_PRE_VOLATILE_WRITE = LOAD_STORE | STORE_STORE; public static final int JMM_POST_VOLATILE_WRITE = STORE_LOAD | STORE_STORE; public static final int JMM_PRE_VOLATILE_READ = 0; public static final int JMM_POST_VOLATILE_READ = LOAD_LOAD | LOAD_STORE; public static String barriersString(int barriers) { StringBuilder sb = new StringBuilder(); sb.append((barriers & LOAD_LOAD) != 0 ? "LOAD_LOAD " : ""); sb.append((barriers & LOAD_STORE) != 0 ? "LOAD_STORE " : ""); sb.append((barriers & STORE_LOAD) != 0 ? "STORE_LOAD " : ""); sb.append((barriers & STORE_STORE) != 0 ? "STORE_STORE " : ""); return sb.toString().trim(); } }