decode_cache.hh revision 8541
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