decode_cache.hh revision 9021:736048daf279 
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.hh"
39
40typedef StaticInstPtr (*DecodeInstFunc)(TheISA::ExtMachInst);
41
42template <DecodeInstFunc decodeInstFunc>
43class DecodeCache
44{
45  private:
46    typedef TheISA::ExtMachInst ExtMachInst;
47
48    /// Hash of decoded instructions.
49    typedef m5::hash_map<ExtMachInst, StaticInstPtr> InstMap;
50    InstMap instMap;
51    struct DecodePage {
52        StaticInstPtr insts[TheISA::PageBytes];
53    };
54
55    /// A store of DecodePages. Basically a slightly smarter hash_map.
56    class DecodePages
57    {
58      protected:
59        typedef typename m5::hash_map<Addr, DecodePage *> PageMap;
60        typedef typename PageMap::iterator PageIt;
61        PageIt recent[2];
62        PageMap pageMap;
63
64        /// Update the small cache of recent lookups.
65        /// @param recentest The most recent result;
66        void
67        update(PageIt recentest)
68        {
69            recent[1] = recent[0];
70            recent[0] = recentest;
71        }
72
73        void
74        addPage(Addr addr, DecodePage *page)
75        {
76            Addr page_addr = addr & ~(TheISA::PageBytes - 1);
77            typename PageMap::value_type to_insert(page_addr, page);
78            update(pageMap.insert(to_insert).first);
79        }
80
81      public:
82        /// Constructor
83        DecodePages()
84        {
85            recent[0] = recent[1] = pageMap.end();
86        }
87
88        /// Attempt to find the DecodePage which goes with a particular
89        /// address. First check the small cache of recent results, then
90        /// actually look in the hash_map.
91        /// @param addr The address to look up.
92        DecodePage *
93        getPage(Addr addr)
94        {
95            Addr page_addr = addr & ~(TheISA::PageBytes - 1);
96
97            // Check against recent lookups.
98            if (recent[0] != pageMap.end()) {
99                if (recent[0]->first == page_addr)
100                    return recent[0]->second;
101                if (recent[1] != pageMap.end() &&
102                        recent[1]->first == page_addr) {
103                    update(recent[1]);
104                    // recent[1] has just become recent[0].
105                    return recent[0]->second;
106                }
107            }
108
109            // Actually look in the has_map.
110            PageIt it = pageMap.find(page_addr);
111            if (it != pageMap.end()) {
112                update(it);
113                return it->second;
114            }
115
116            // Didn't find an existing page, so add a new one.
117            DecodePage *newPage = new DecodePage;
118            addPage(page_addr, newPage);
119            return newPage;
120        }
121    } decodePages;
122
123  public:
124    /// Decode a machine instruction.
125    /// @param mach_inst The binary instruction to decode.
126    /// @retval A pointer to the corresponding StaticInst object.
127    StaticInstPtr
128    decode(ExtMachInst mach_inst, Addr addr)
129    {
130        // Try to find a matching address based table of instructions.
131        DecodePage *page = decodePages.getPage(addr);
132
133        // Use the table to decode the instruction. It will fall back to other
134        // mechanisms if it needs to.
135        Addr offset = addr & (TheISA::PageBytes - 1);
136        StaticInstPtr si = page->insts[offset];
137        if (si && (si->machInst == mach_inst))
138            return si;
139
140        InstMap::iterator iter = instMap.find(mach_inst);
141        if (iter != instMap.end()) {
142            si = iter->second;
143            page->insts[offset] = si;
144            return si;
145        }
146
147        si = decodeInstFunc(mach_inst);
148        instMap[mach_inst] = si;
149        page->insts[offset] = si;
150        return si;
151    }
152};
153
154#endif // __CPU_DECODE_CACHE_HH__
155