decode.hh revision 2863
1/* 2 * Copyright (c) 2004-2006 The Regents of The University of Michigan 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: Kevin Lim 29 */ 30 31#ifndef __CPU_O3_DECODE_HH__ 32#define __CPU_O3_DECODE_HH__ 33 34#include <queue> 35 36#include "base/statistics.hh" 37#include "base/timebuf.hh" 38 39/** 40 * DefaultDecode class handles both single threaded and SMT 41 * decode. Its width is specified by the parameters; each cycles it 42 * tries to decode that many instructions. Because instructions are 43 * actually decoded when the StaticInst is created, this stage does 44 * not do much other than check any PC-relative branches. 45 */ 46template<class Impl> 47class DefaultDecode 48{ 49 private: 50 // Typedefs from the Impl. 51 typedef typename Impl::O3CPU O3CPU; 52 typedef typename Impl::DynInstPtr DynInstPtr; 53 typedef typename Impl::Params Params; 54 typedef typename Impl::CPUPol CPUPol; 55 56 // Typedefs from the CPU policy. 57 typedef typename CPUPol::FetchStruct FetchStruct; 58 typedef typename CPUPol::DecodeStruct DecodeStruct; 59 typedef typename CPUPol::TimeStruct TimeStruct; 60 61 public: 62 /** Overall decode stage status. Used to determine if the CPU can 63 * deschedule itself due to a lack of activity. 64 */ 65 enum DecodeStatus { 66 Active, 67 Inactive 68 }; 69 70 /** Individual thread status. */ 71 enum ThreadStatus { 72 Running, 73 Idle, 74 StartSquash, 75 Squashing, 76 Blocked, 77 Unblocking 78 }; 79 80 private: 81 /** Decode status. */ 82 DecodeStatus _status; 83 84 /** Per-thread status. */ 85 ThreadStatus decodeStatus[Impl::MaxThreads]; 86 87 public: 88 /** DefaultDecode constructor. */ 89 DefaultDecode(Params *params); 90 91 /** Returns the name of decode. */ 92 std::string name() const; 93 94 /** Registers statistics. */ 95 void regStats(); 96 97 /** Sets CPU pointer. */ 98 void setCPU(O3CPU *cpu_ptr); 99 100 /** Sets the main backwards communication time buffer pointer. */ 101 void setTimeBuffer(TimeBuffer<TimeStruct> *tb_ptr); 102 103 /** Sets pointer to time buffer used to communicate to the next stage. */ 104 void setDecodeQueue(TimeBuffer<DecodeStruct> *dq_ptr); 105 106 /** Sets pointer to time buffer coming from fetch. */ 107 void setFetchQueue(TimeBuffer<FetchStruct> *fq_ptr); 108 109 /** Sets pointer to list of active threads. */ 110 void setActiveThreads(std::list<unsigned> *at_ptr); 111 112 /** Drains the decode stage. */ 113 bool drain(); 114 115 /** Resumes execution after a drain. */ 116 void resume() { } 117 118 /** Switches out the decode stage. */ 119 void switchOut() { } 120 121 /** Takes over from another CPU's thread. */ 122 void takeOverFrom(); 123 124 /** Ticks decode, processing all input signals and decoding as many 125 * instructions as possible. 126 */ 127 void tick(); 128 129 /** Determines what to do based on decode's current status. 130 * @param status_change decode() sets this variable if there was a status 131 * change (ie switching from from blocking to unblocking). 132 * @param tid Thread id to decode instructions from. 133 */ 134 void decode(bool &status_change, unsigned tid); 135 136 /** Processes instructions from fetch and passes them on to rename. 137 * Decoding of instructions actually happens when they are created in 138 * fetch, so this function mostly checks if PC-relative branches are 139 * correct. 140 */ 141 void decodeInsts(unsigned tid); 142 143 private: 144 /** Inserts a thread's instructions into the skid buffer, to be decoded 145 * once decode unblocks. 146 */ 147 void skidInsert(unsigned tid); 148 149 /** Returns if all of the skid buffers are empty. */ 150 bool skidsEmpty(); 151 152 /** Updates overall decode status based on all of the threads' statuses. */ 153 void updateStatus(); 154 155 /** Separates instructions from fetch into individual lists of instructions 156 * sorted by thread. 157 */ 158 void sortInsts(); 159 160 /** Reads all stall signals from the backwards communication timebuffer. */ 161 void readStallSignals(unsigned tid); 162 163 /** Checks all input signals and updates decode's status appropriately. */ 164 bool checkSignalsAndUpdate(unsigned tid); 165 166 /** Checks all stall signals, and returns if any are true. */ 167 bool checkStall(unsigned tid) const; 168 169 /** Returns if there any instructions from fetch on this cycle. */ 170 inline bool fetchInstsValid(); 171 172 /** Switches decode to blocking, and signals back that decode has 173 * become blocked. 174 * @return Returns true if there is a status change. 175 */ 176 bool block(unsigned tid); 177 178 /** Switches decode to unblocking if the skid buffer is empty, and 179 * signals back that decode has unblocked. 180 * @return Returns true if there is a status change. 181 */ 182 bool unblock(unsigned tid); 183 184 /** Squashes if there is a PC-relative branch that was predicted 185 * incorrectly. Sends squash information back to fetch. 186 */ 187 void squash(DynInstPtr &inst, unsigned tid); 188 189 public: 190 /** Squashes due to commit signalling a squash. Changes status to 191 * squashing and clears block/unblock signals as needed. 192 */ 193 unsigned squash(unsigned tid); 194 195 private: 196 // Interfaces to objects outside of decode. 197 /** CPU interface. */ 198 O3CPU *cpu; 199 200 /** Time buffer interface. */ 201 TimeBuffer<TimeStruct> *timeBuffer; 202 203 /** Wire to get rename's output from backwards time buffer. */ 204 typename TimeBuffer<TimeStruct>::wire fromRename; 205 206 /** Wire to get iew's information from backwards time buffer. */ 207 typename TimeBuffer<TimeStruct>::wire fromIEW; 208 209 /** Wire to get commit's information from backwards time buffer. */ 210 typename TimeBuffer<TimeStruct>::wire fromCommit; 211 212 /** Wire to write information heading to previous stages. */ 213 // Might not be the best name as not only fetch will read it. 214 typename TimeBuffer<TimeStruct>::wire toFetch; 215 216 /** Decode instruction queue. */ 217 TimeBuffer<DecodeStruct> *decodeQueue; 218 219 /** Wire used to write any information heading to rename. */ 220 typename TimeBuffer<DecodeStruct>::wire toRename; 221 222 /** Fetch instruction queue interface. */ 223 TimeBuffer<FetchStruct> *fetchQueue; 224 225 /** Wire to get fetch's output from fetch queue. */ 226 typename TimeBuffer<FetchStruct>::wire fromFetch; 227 228 /** Queue of all instructions coming from fetch this cycle. */ 229 std::queue<DynInstPtr> insts[Impl::MaxThreads]; 230 231 /** Skid buffer between fetch and decode. */ 232 std::queue<DynInstPtr> skidBuffer[Impl::MaxThreads]; 233 234 /** Variable that tracks if decode has written to the time buffer this 235 * cycle. Used to tell CPU if there is activity this cycle. 236 */ 237 bool wroteToTimeBuffer; 238 239 /** Source of possible stalls. */ 240 struct Stalls { 241 bool rename; 242 bool iew; 243 bool commit; 244 }; 245 246 /** Tracks which stages are telling decode to stall. */ 247 Stalls stalls[Impl::MaxThreads]; 248 249 /** Rename to decode delay, in ticks. */ 250 unsigned renameToDecodeDelay; 251 252 /** IEW to decode delay, in ticks. */ 253 unsigned iewToDecodeDelay; 254 255 /** Commit to decode delay, in ticks. */ 256 unsigned commitToDecodeDelay; 257 258 /** Fetch to decode delay, in ticks. */ 259 unsigned fetchToDecodeDelay; 260 261 /** The width of decode, in instructions. */ 262 unsigned decodeWidth; 263 264 /** Index of instructions being sent to rename. */ 265 unsigned toRenameIndex; 266 267 /** number of Active Threads*/ 268 unsigned numThreads; 269 270 /** List of active thread ids */ 271 std::list<unsigned> *activeThreads; 272 273 /** Number of branches in flight. */ 274 unsigned branchCount[Impl::MaxThreads]; 275 276 /** Maximum size of the skid buffer. */ 277 unsigned skidBufferMax; 278 279 /** Stat for total number of idle cycles. */ 280 Stats::Scalar<> decodeIdleCycles; 281 /** Stat for total number of blocked cycles. */ 282 Stats::Scalar<> decodeBlockedCycles; 283 /** Stat for total number of normal running cycles. */ 284 Stats::Scalar<> decodeRunCycles; 285 /** Stat for total number of unblocking cycles. */ 286 Stats::Scalar<> decodeUnblockCycles; 287 /** Stat for total number of squashing cycles. */ 288 Stats::Scalar<> decodeSquashCycles; 289 /** Stat for number of times a branch is resolved at decode. */ 290 Stats::Scalar<> decodeBranchResolved; 291 /** Stat for number of times a branch mispredict is detected. */ 292 Stats::Scalar<> decodeBranchMispred; 293 /** Stat for number of times decode detected a non-control instruction 294 * incorrectly predicted as a branch. 295 */ 296 Stats::Scalar<> decodeControlMispred; 297 /** Stat for total number of decoded instructions. */ 298 Stats::Scalar<> decodeDecodedInsts; 299 /** Stat for total number of squashed instructions. */ 300 Stats::Scalar<> decodeSquashedInsts; 301}; 302 303#endif // __CPU_O3_DECODE_HH__ 304