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