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