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 "arch/isa_traits.hh"
  35 #include "arch/types.hh"
  36 #include "base/hashmap.hh"
  37 #include "config/the_isa.hh"
  38 #include "cpu/static_inst.hh"
  39
  40 typedef StaticInstPtr (*DecodeInstFunc)(TheISA::ExtMachInst);
  41
  42 template <DecodeInstFunc decodeInstFunc>
  43 class DecodeCache
  44 {
  45   private:
  46     typedef TheISA::ExtMachInst ExtMachInst;
  47
  48     /// Hash of decoded instructions.
  49     typedef m5::hash_map<ExtMachInst, StaticInstPtr> InstMap;
  50     InstMap instMap;
  51
  52     /// A table of instructions which are already been decoded, indexed by
  53     /// page offset.
  54     class DecodePage
  55     {
  56       protected:
  57         StaticInstPtr instructions[TheISA::PageBytes];
  58
  59         // A helper function to compute the index of an address in the table.
  60         Addr offset(Addr addr) { return addr & (TheISA::PageBytes - 1); }
  61
  62       public:
  63         /// Decode the given instruction. First attempt to find it in the
  64         /// table, then in the generic decode cache, and finally call the
  65         /// actual decode function.
  66         ///
  67         /// @param mach_inst The predecoded instruction to decode.
  68         /// @param addr The address the instruction came from.
  69         /// @param cache A cache of already decoded instructions.
  70         /// @retval The decoded instruction object.
  71         StaticInstPtr
  72         decode(const ExtMachInst &mach_inst, Addr addr, InstMap &instMap)
  73         {
  74             StaticInstPtr si = instructions[offset(addr)];
  75             if (si && (si->machInst == mach_inst)) {
  76                 return si;
  77             }
  78
  79             InstMap::iterator iter = instMap.find(mach_inst);
  80             if (iter != instMap.end()) {
  81                 si = iter->second;
  82             } else {
  83                 si = decodeInstFunc(mach_inst);
  84                 instMap[mach_inst] = si;
  85             }
  86
  87             instructions[offset(addr)] = si;
  88             return si;
  89         }
  90     };
  91
  92     /// A store of DecodePages. Basically a slightly smarter hash_map.
  93     class DecodePages
  94     {
  95       protected:
  96         typedef typename m5::hash_map<Addr, DecodePage *> PageMap;
  97         typedef typename PageMap::iterator PageIt;
  98         PageIt recent[2];
  99         PageMap pageMap;
 100
 101         /// Update the small cache of recent lookups.
 102         /// @param recentest The most recent result;
 103         void
 104         update(PageIt recentest)
 105         {
 106             recent[1] = recent[0];
 107             recent[0] = recentest;
 108         }
 109
 110       public:
 111         /// Constructor
 112         DecodePages()
 113         {
 114             recent[0] = recent[1] = pageMap.end();
 115         }
 116
 117         /// Attempt to find the DecodePage which goes with a particular
 118         /// address. First check the small cache of recent results, then
 119         /// actually look in the hash_map.
 120         /// @param addr The address to look up.
 121         DecodePage *
 122         findPage(Addr addr)
 123         {
 124             Addr page_addr = addr & ~(TheISA::PageBytes - 1);
 125
 126             // Check against recent lookups.
 127             if (recent[0] != pageMap.end()) {
 128                 if (recent[0]->first == page_addr)
 129                     return recent[0]->second;
 130                 if (recent[1] != pageMap.end() &&
 131                         recent[1]->first == page_addr) {
 132                     update(recent[1]);
 133                     // recent[1] has just become recent[0].
 134                     return recent[0]->second;
 135                 }
 136             }
 137
 138             // Actually look in the has_map.
 139             PageIt it = pageMap.find(page_addr);
 140             if (it != pageMap.end()) {
 141                 update(it);
 142                 return it->second;
 143             }
 144
 145             // Didn't find it so return NULL.
 146             return NULL;
 147         }
 148
 149         void
 150         addPage(Addr addr, DecodePage *page)
 151         {
 152             Addr page_addr = addr & ~(TheISA::PageBytes - 1);
 153             typename PageMap::value_type to_insert(page_addr, page);
 154             update(pageMap.insert(to_insert).first);
 155         }
 156     } decodePages;
 157
 158   public:
 159     /// Decode a machine instruction.
 160     /// @param mach_inst The binary instruction to decode.
 161     /// @retval A pointer to the corresponding StaticInst object.
 162     StaticInstPtr
 163     decode(ExtMachInst mach_inst, Addr addr)
 164     {
 165         // Try to find a matching address based table of instructions.
 166         DecodePage *page = decodePages.findPage(addr);
 167         if (!page) {
 168             // Nothing was found, so create a new one.
 169             page = new DecodePage;
 170             decodePages.addPage(addr, page);
 171         }
 172
 173         // Use the table to decode the instruction. It will fall back to other
 174         // mechanisms if it needs to.
 175         return page->decode(mach_inst, addr, instMap);
 176     }
 177 };
 178
 179 #endif // __CPU_DECODE_CACHE_HH__