xref: /gem5/src/cpu/decode_cache.hh

/*
 * Copyright (c) 2011 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
 */

#ifndef __CPU_DECODE_CACHE_HH__
#define __CPU_DECODE_CACHE_HH__

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

typedef StaticInstPtr (*DecodeInstFunc)(TheISA::ExtMachInst);

template <DecodeInstFunc decodeInstFunc>
class DecodeCache
{
  private:
    typedef TheISA::ExtMachInst ExtMachInst;

    /// Hash of decoded instructions.
    typedef m5::hash_map<ExtMachInst, StaticInstPtr> InstMap;
    InstMap instMap;
    struct DecodePage {
        StaticInstPtr insts[TheISA::PageBytes];
    };

    /// A store of DecodePages. Basically a slightly smarter hash_map.
    class DecodePages
    {
      protected:
        typedef typename m5::hash_map<Addr, DecodePage *> PageMap;
        typedef typename PageMap::iterator PageIt;
        PageIt recent[2];
        PageMap pageMap;

        /// Update the small cache of recent lookups.
        /// @param recentest The most recent result;
        void
        update(PageIt recentest)
        {
            recent[1] = recent[0];
            recent[0] = recentest;
        }

        void
        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);
        }

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

        /// Attempt to find the DecodePage which goes with a particular
        /// address. First check the small cache of recent results, then
        /// actually look in the hash_map.
        /// @param addr The address to look up.
        DecodePage *
        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;
        }
    } decodePages;

  public:
    /// Decode a machine instruction.
    /// @param mach_inst The binary instruction to decode.
    /// @retval A pointer to the corresponding StaticInst object.
    StaticInstPtr
    decode(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 = decodeInstFunc(mach_inst);
        instMap[mach_inst] = si;
        page->insts[offset] = si;
        return si;
    }
};

#endif // __CPU_DECODE_CACHE_HH__