gem5/src/cpu/decode_cache.cc

/*
 * Copyright (c) 2011-2012 Google
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met: redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer;
 * redistributions in binary form must reproduce the above copyright
 * notice, this list of conditions and the following disclaimer in the
 * documentation and/or other materials provided with the distribution;
 * neither the name of the copyright holders nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * Authors: Gabe Black
 */

#include "arch/decoder.hh"
#include "arch/isa_traits.hh"
#include "arch/types.hh"
#include "base/hashmap.hh"
#include "config/the_isa.hh"
#include "cpu/static_inst.hh"

void
DecodeCache::DecodePages::update(PageIt recentest)
{
    recent[1] = recent[0];
    recent[0] = recentest;
}

void
DecodeCache::DecodePages::addPage(Addr addr, DecodePage *page)
{
    Addr page_addr = addr & ~(TheISA::PageBytes - 1);
    typename PageMap::value_type to_insert(page_addr, page);
    update(pageMap.insert(to_insert).first);
}

DecodeCache::DecodePages::DecodePages()
{
    recent[0] = recent[1] = pageMap.end();
}

DecodeCache::DecodePage *
DecodeCache::DecodePages::getPage(Addr addr)
{
    Addr page_addr = addr & ~(TheISA::PageBytes - 1);

    // Check against recent lookups.
    if (recent[0] != pageMap.end()) {
        if (recent[0]->first == page_addr)
            return recent[0]->second;
        if (recent[1] != pageMap.end() &&
                recent[1]->first == page_addr) {
            update(recent[1]);
            // recent[1] has just become recent[0].
            return recent[0]->second;
        }
    }

    // Actually look in the has_map.
    PageIt it = pageMap.find(page_addr);
    if (it != pageMap.end()) {
        update(it);
        return it->second;
    }

    // Didn't find an existing page, so add a new one.
    DecodePage *newPage = new DecodePage;
    addPage(page_addr, newPage);
    return newPage;
}

StaticInstPtr
DecodeCache::decode(TheISA::Decoder *decoder,
        ExtMachInst mach_inst, Addr addr)
{
    // Try to find a matching address based table of instructions.
    DecodePage *page = decodePages.getPage(addr);

    // Use the table to decode the instruction. It will fall back to other
    // mechanisms if it needs to.
    Addr offset = addr & (TheISA::PageBytes - 1);
    StaticInstPtr si = page->insts[offset];
    if (si && (si->machInst == mach_inst))
        return si;

    InstMap::iterator iter = instMap.find(mach_inst);
    if (iter != instMap.end()) {
        si = iter->second;
        page->insts[offset] = si;
        return si;
    }

    si = decoder->decodeInst(mach_inst);
    instMap[mach_inst] = si;
    page->insts[offset] = si;
    return si;
}