decode_cache.hh revision 9024:5851586f399c 
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 "arch/isa_traits.hh"
35#include "arch/types.hh"
36#include "base/hashmap.hh"
37#include "config/the_isa.hh"
38#include "cpu/static_inst_fwd.hh"
39
40namespace TheISA
41{
42    class Decoder;
43}
44
45namespace DecodeCache
46{
47
48/// Hash for decoded instructions.
49typedef m5::hash_map<TheISA::ExtMachInst, StaticInstPtr> InstMap;
50
51/// A sparse map from an Addr to a Value, stored in page chunks.
52template<class Value>
53class AddrMap
54{
55  protected:
56    // A pages worth of cache entries.
57    struct CachePage {
58        Value items[TheISA::PageBytes];
59    };
60    // A map of cache pages which allows a sparse mapping.
61    typedef typename m5::hash_map<Addr, CachePage *> PageMap;
62    typedef typename PageMap::iterator PageIt;
63    // Mini cache of recent lookups.
64    PageIt recent[2];
65    PageMap pageMap;
66
67    /// Update the mini cache of recent lookups.
68    /// @param recentest The most recent result;
69    void
70    update(PageIt recentest)
71    {
72        recent[1] = recent[0];
73        recent[0] = recentest;
74    }
75
76    /// Attempt to find the CacheePage which goes with a particular
77    /// address. First check the small cache of recent results, then
78    /// actually look in the hash_map.
79    /// @param addr The address to look up.
80    CachePage *
81    getPage(Addr addr)
82    {
83        Addr page_addr = addr & ~(TheISA::PageBytes - 1);
84
85        // Check against recent lookups.
86        if (recent[0] != pageMap.end()) {
87            if (recent[0]->first == page_addr)
88                return recent[0]->second;
89            if (recent[1] != pageMap.end() &&
90                    recent[1]->first == page_addr) {
91                update(recent[1]);
92                // recent[1] has just become recent[0].
93                return recent[0]->second;
94            }
95        }
96
97        // Actually look in the has_map.
98        PageIt it = pageMap.find(page_addr);
99        if (it != pageMap.end()) {
100            update(it);
101            return it->second;
102        }
103
104        // Didn't find an existing page, so add a new one.
105        CachePage *newPage = new CachePage;
106        page_addr = page_addr & ~(TheISA::PageBytes - 1);
107        typename PageMap::value_type to_insert(page_addr, newPage);
108        update(pageMap.insert(to_insert).first);
109        return newPage;
110    }
111
112  public:
113    /// Constructor
114    AddrMap()
115    {
116        recent[0] = recent[1] = pageMap.end();
117    }
118
119    Value &
120    lookup(Addr addr)
121    {
122        CachePage *page = getPage(addr);
123        return page->items[addr & (TheISA::PageBytes - 1)];
124    }
125};
126
127} // namespace DecodeCache
128
129#endif // __CPU_DECODE_CACHE_HH__
130