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