src/cpu/decode_cache.hh

   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
  29 #ifndef __CPU_DECODE_CACHE_HH__
  30 #define __CPU_DECODE_CACHE_HH__
  31
  32 #include <unordered_map>
  33
  34 #include "base/bitfield.hh"
  35 #include "cpu/static_inst_fwd.hh"
  36
  37 namespace DecodeCache
  38 {
  39
  40 /// Hash for decoded instructions.
  41 template <typename EMI>
  42 using InstMap = std::unordered_map<EMI, StaticInstPtr>;
  43
  44 /// A sparse map from an Addr to a Value, stored in page chunks.
  45 template<class Value, Addr CacheChunkShift = 12>
  46 class AddrMap
  47 {
  48   protected:
  49     static constexpr Addr CacheChunkBytes = 1ULL << CacheChunkShift;
  50
  51     static constexpr Addr
  52     chunkOffset(Addr addr)
  53     {
  54         return addr & (CacheChunkBytes - 1);
  55     }
  56
  57     static constexpr Addr
  58     chunkStart(Addr addr)
  59     {
  60         return addr & ~(CacheChunkBytes - 1);
  61     }
  62
  63     // A chunk of cache entries.
  64     struct CacheChunk
  65     {
  66         Value items[CacheChunkBytes];
  67     };
  68     // A map of cache chunks which allows a sparse mapping.
  69     typedef typename std::unordered_map<Addr, CacheChunk *> ChunkMap;
  70     typedef typename ChunkMap::iterator ChunkIt;
  71     // Mini cache of recent lookups.
  72     ChunkIt recent[2];
  73     ChunkMap chunkMap;
  74
  75     /// Update the mini cache of recent lookups.
  76     /// @param recentest The most recent result;
  77     void
  78     update(ChunkIt recentest)
  79     {
  80         recent[1] = recent[0];
  81         recent[0] = recentest;
  82     }
  83
  84     /// Attempt to find the CacheChunk which goes with a particular
  85     /// address. First check the small cache of recent results, then
  86     /// actually look in the hash map.
  87     /// @param addr The address to look up.
  88     CacheChunk *
  89     getChunk(Addr addr)
  90     {
  91         Addr chunk_addr = chunkStart(addr);
  92
  93         // Check against recent lookups.
  94         if (recent[0] != chunkMap.end()) {
  95             if (recent[0]->first == chunk_addr)
  96                 return recent[0]->second;
  97             if (recent[1] != chunkMap.end() &&
  98                     recent[1]->first == chunk_addr) {
  99                 update(recent[1]);
 100                 // recent[1] has just become recent[0].
 101                 return recent[0]->second;
 102             }
 103         }
 104
 105         // Actually look in the hash_map.
 106         ChunkIt it = chunkMap.find(chunk_addr);
 107         if (it != chunkMap.end()) {
 108             update(it);
 109             return it->second;
 110         }
 111
 112         // Didn't find an existing chunk, so add a new one.
 113         CacheChunk *newChunk = new CacheChunk;
 114         typename ChunkMap::value_type to_insert(chunk_addr, newChunk);
 115         update(chunkMap.insert(to_insert).first);
 116         return newChunk;
 117     }
 118
 119   public:
 120     /// Constructor
 121     AddrMap()
 122     {
 123         recent[0] = recent[1] = chunkMap.end();
 124     }
 125
 126     Value &
 127     lookup(Addr addr)
 128     {
 129         CacheChunk *chunk = getChunk(addr);
 130         return chunk->items[chunkOffset(addr)];
 131     }
 132 };
 133
 134 } // namespace DecodeCache
 135
 136 #endif // __CPU_DECODE_CACHE_HH__