decode_cache.hh revision 8541:27aaee8ec7cc 
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
52    /// A table of instructions which are already been decoded, indexed by
53    /// page offset.
54    class DecodePage
55    {
56      protected:
57        StaticInstPtr instructions[TheISA::PageBytes];
58
59        // A helper function to compute the index of an address in the table.
60        Addr offset(Addr addr) { return addr & (TheISA::PageBytes - 1); }
61
62      public:
63        /// Decode the given instruction. First attempt to find it in the
64        /// table, then in the generic decode cache, and finally call the
65        /// actual decode function.
66        ///
67        /// @param mach_inst The predecoded instruction to decode.
68        /// @param addr The address the instruction came from.
69        /// @param cache A cache of already decoded instructions.
70        /// @retval The decoded instruction object.
71        StaticInstPtr
72        decode(const ExtMachInst &mach_inst, Addr addr, InstMap &instMap)
73        {
74            StaticInstPtr si = instructions[offset(addr)];
75            if (si && (si->machInst == mach_inst)) {
76                return si;
77            }
78
79            InstMap::iterator iter = instMap.find(mach_inst);
80            if (iter != instMap.end()) {
81                si = iter->second;
82            } else {
83                si = decodeInstFunc(mach_inst);
84                instMap[mach_inst] = si;
85            }
86
87            instructions[offset(addr)] = si;
88            return si;
89        }
90    };
91
92    /// A store of DecodePages. Basically a slightly smarter hash_map.
93    class DecodePages
94    {
95      protected:
96        typedef typename m5::hash_map<Addr, DecodePage *> PageMap;
97        typedef typename PageMap::iterator PageIt;
98        PageIt recent[2];
99        PageMap pageMap;
100
101        /// Update the small cache of recent lookups.
102        /// @param recentest The most recent result;
103        void
104        update(PageIt recentest)
105        {
106            recent[1] = recent[0];
107            recent[0] = recentest;
108        }
109
110      public:
111        /// Constructor
112        DecodePages()
113        {
114            recent[0] = recent[1] = pageMap.end();
115        }
116
117        /// Attempt to find the DecodePage which goes with a particular
118        /// address. First check the small cache of recent results, then
119        /// actually look in the hash_map.
120        /// @param addr The address to look up.
121        DecodePage *
122        findPage(Addr addr)
123        {
124            Addr page_addr = addr & ~(TheISA::PageBytes - 1);
125
126            // Check against recent lookups.
127            if (recent[0] != pageMap.end()) {
128                if (recent[0]->first == page_addr)
129                    return recent[0]->second;
130                if (recent[1] != pageMap.end() &&
131                        recent[1]->first == page_addr) {
132                    update(recent[1]);
133                    // recent[1] has just become recent[0].
134                    return recent[0]->second;
135                }
136            }
137
138            // Actually look in the has_map.
139            PageIt it = pageMap.find(page_addr);
140            if (it != pageMap.end()) {
141                update(it);
142                return it->second;
143            }
144
145            // Didn't find it so return NULL.
146            return NULL;
147        }
148
149        void
150        addPage(Addr addr, DecodePage *page)
151        {
152            Addr page_addr = addr & ~(TheISA::PageBytes - 1);
153            typename PageMap::value_type to_insert(page_addr, page);
154            update(pageMap.insert(to_insert).first);
155        }
156    } decodePages;
157
158  public:
159    /// Decode a machine instruction.
160    /// @param mach_inst The binary instruction to decode.
161    /// @retval A pointer to the corresponding StaticInst object.
162    StaticInstPtr
163    decode(ExtMachInst mach_inst, Addr addr)
164    {
165        // Try to find a matching address based table of instructions.
166        DecodePage *page = decodePages.findPage(addr);
167        if (!page) {
168            // Nothing was found, so create a new one.
169            page = new DecodePage;
170            decodePages.addPage(addr, page);
171        }
172
173        // Use the table to decode the instruction. It will fall back to other
174        // mechanisms if it needs to.
175        return page->decode(mach_inst, addr, instMap);
176    }
177};
178
179#endif // __CPU_DECODE_CACHE_HH__
180