decode_cache.hh revision 11168:f98eb2da15a4 
1/*
2 * Copyright (c) 2011 Google
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions are
7 * met: redistributions of source code must retain the above copyright
8 * notice, this list of conditions and the following disclaimer;
9 * redistributions in binary form must reproduce the above copyright
10 * notice, this list of conditions and the following disclaimer in the
11 * documentation and/or other materials provided with the distribution;
12 * neither the name of the copyright holders nor the names of its
13 * contributors may be used to endorse or promote products derived from
14 * this software without specific prior written permission.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
17 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
18 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
19 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
20 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
21 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
22 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
23 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
24 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
25 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
26 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27 *
28 * Authors: Gabe Black
29 */
30
31#ifndef __CPU_DECODE_CACHE_HH__
32#define __CPU_DECODE_CACHE_HH__
33
34#include <unordered_map>
35
36#include "arch/isa_traits.hh"
37#include "arch/types.hh"
38#include "config/the_isa.hh"
39#include "cpu/static_inst_fwd.hh"
40
41namespace TheISA
42{
43    class Decoder;
44}
45
46namespace DecodeCache
47{
48
49/// Hash for decoded instructions.
50typedef std::unordered_map<TheISA::ExtMachInst, StaticInstPtr> InstMap;
51
52/// A sparse map from an Addr to a Value, stored in page chunks.
53template<class Value>
54class AddrMap
55{
56  protected:
57    // A pages worth of cache entries.
58    struct CachePage {
59        Value items[TheISA::PageBytes];
60    };
61    // A map of cache pages which allows a sparse mapping.
62    typedef typename std::unordered_map<Addr, CachePage *> PageMap;
63    typedef typename PageMap::iterator PageIt;
64    // Mini cache of recent lookups.
65    PageIt recent[2];
66    PageMap pageMap;
67
68    /// Update the mini cache of recent lookups.
69    /// @param recentest The most recent result;
70    void
71    update(PageIt recentest)
72    {
73        recent[1] = recent[0];
74        recent[0] = recentest;
75    }
76
77    /// Attempt to find the CacheePage which goes with a particular
78    /// address. First check the small cache of recent results, then
79    /// actually look in the hash map.
80    /// @param addr The address to look up.
81    CachePage *
82    getPage(Addr addr)
83    {
84        Addr page_addr = addr & ~(TheISA::PageBytes - 1);
85
86        // Check against recent lookups.
87        if (recent[0] != pageMap.end()) {
88            if (recent[0]->first == page_addr)
89                return recent[0]->second;
90            if (recent[1] != pageMap.end() &&
91                    recent[1]->first == page_addr) {
92                update(recent[1]);
93                // recent[1] has just become recent[0].
94                return recent[0]->second;
95            }
96        }
97
98        // Actually look in the has_map.
99        PageIt it = pageMap.find(page_addr);
100        if (it != pageMap.end()) {
101            update(it);
102            return it->second;
103        }
104
105        // Didn't find an existing page, so add a new one.
106        CachePage *newPage = new CachePage;
107        page_addr = page_addr & ~(TheISA::PageBytes - 1);
108        typename PageMap::value_type to_insert(page_addr, newPage);
109        update(pageMap.insert(to_insert).first);
110        return newPage;
111    }
112
113  public:
114    /// Constructor
115    AddrMap()
116    {
117        recent[0] = recent[1] = pageMap.end();
118    }
119
120    Value &
121    lookup(Addr addr)
122    {
123        CachePage *page = getPage(addr);
124        return page->items[addr & (TheISA::PageBytes - 1)];
125    }
126};
127
128} // namespace DecodeCache
129
130#endif // __CPU_DECODE_CACHE_HH__
131