decode_cache.hh

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/*
 * Copyright (c) 2011 Google
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 * neither the name of the copyright holders nor the names of its
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#ifndef __CPU_DECODE_CACHE_HH__
#define __CPU_DECODE_CACHE_HH__

#include <unordered_map>

#include "arch/isa_traits.hh"
#include "arch/types.hh"
#include "config/the_isa.hh"
#include "cpu/static_inst_fwd.hh"

namespace TheISA
{
    class Decoder;
}

namespace DecodeCache
{

template <typename EMI>
using InstMap = std::unordered_map<EMI, StaticInstPtr>;

template<class Value>
class AddrMap
{
  protected:
    // A pages worth of cache entries.
    struct CachePage {
        Value items[TheISA::PageBytes];
    };
    // A map of cache pages which allows a sparse mapping.
    typedef typename std::unordered_map<Addr, CachePage *> PageMap;
    typedef typename PageMap::iterator PageIt;
    // Mini cache of recent lookups.
    PageIt recent[2];
    PageMap pageMap;

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

    CachePage *
    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.
        CachePage *newPage = new CachePage;
        page_addr = page_addr & ~(TheISA::PageBytes - 1);
        typename PageMap::value_type to_insert(page_addr, newPage);
        update(pageMap.insert(to_insert).first);
        return newPage;
    }

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

    Value &
    lookup(Addr addr)
    {
        CachePage *page = getPage(addr);
        return page->items[addr & (TheISA::PageBytes - 1)];
    }
};

} // namespace DecodeCache

#endif // __CPU_DECODE_CACHE_HH__