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/*
* Copyright (c) 2011 Google
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met: redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer;
* redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution;
* neither the name of the copyright holders nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
* Authors: Gabe Black
*/
#ifndef __CPU_DECODE_CACHE_HH__
#define __CPU_DECODE_CACHE_HH__
#include "arch/isa_traits.hh"
#include "arch/types.hh"
#include "base/hashmap.hh"
#include "config/the_isa.hh"
#include "cpu/static_inst.hh"
typedef StaticInstPtr (*DecodeInstFunc)(TheISA::ExtMachInst);
template <DecodeInstFunc decodeInstFunc>
class DecodeCache
{
private:
typedef TheISA::ExtMachInst ExtMachInst;
/// Hash of decoded instructions.
typedef m5::hash_map<ExtMachInst, StaticInstPtr> InstMap;
InstMap instMap;
/// A table of instructions which are already been decoded, indexed by
/// page offset.
class DecodePage
{
protected:
StaticInstPtr instructions[TheISA::PageBytes];
// A helper function to compute the index of an address in the table.
Addr offset(Addr addr) { return addr & (TheISA::PageBytes - 1); }
public:
/// Decode the given instruction. First attempt to find it in the
/// table, then in the generic decode cache, and finally call the
/// actual decode function.
///
/// @param mach_inst The predecoded instruction to decode.
/// @param addr The address the instruction came from.
/// @param cache A cache of already decoded instructions.
/// @retval The decoded instruction object.
StaticInstPtr
decode(const ExtMachInst &mach_inst, Addr addr, InstMap &instMap)
{
StaticInstPtr si = instructions[offset(addr)];
if (si && (si->machInst == mach_inst)) {
return si;
}
InstMap::iterator iter = instMap.find(mach_inst);
if (iter != instMap.end()) {
si = iter->second;
} else {
si = decodeInstFunc(mach_inst);
instMap[mach_inst] = si;
}
instructions[offset(addr)] = si;
return si;
}
};
/// A store of DecodePages. Basically a slightly smarter hash_map.
class DecodePages
{
protected:
typedef typename m5::hash_map<Addr, DecodePage *> PageMap;
typedef typename PageMap::iterator PageIt;
PageIt recent[2];
PageMap pageMap;
/// Update the small cache of recent lookups.
/// @param recentest The most recent result;
void
update(PageIt recentest)
{
recent[1] = recent[0];
recent[0] = recentest;
}
public:
/// Constructor
DecodePages()
{
recent[0] = recent[1] = pageMap.end();
}
/// Attempt to find the DecodePage which goes with a particular
/// address. First check the small cache of recent results, then
/// actually look in the hash_map.
/// @param addr The address to look up.
DecodePage *
findPage(Addr addr)
{
Addr page_addr = addr & ~(TheISA::PageBytes - 1);
// Check against recent lookups.
if (recent[0] != pageMap.end()) {
if (recent[0]->first == page_addr)
return recent[0]->second;
if (recent[1] != pageMap.end() &&
recent[1]->first == page_addr) {
update(recent[1]);
// recent[1] has just become recent[0].
return recent[0]->second;
}
}
// Actually look in the has_map.
PageIt it = pageMap.find(page_addr);
if (it != pageMap.end()) {
update(it);
return it->second;
}
// Didn't find it so return NULL.
return NULL;
}
void
addPage(Addr addr, DecodePage *page)
{
Addr page_addr = addr & ~(TheISA::PageBytes - 1);
typename PageMap::value_type to_insert(page_addr, page);
update(pageMap.insert(to_insert).first);
}
} decodePages;
public:
/// Decode a machine instruction.
/// @param mach_inst The binary instruction to decode.
/// @retval A pointer to the corresponding StaticInst object.
StaticInstPtr
decode(ExtMachInst mach_inst, Addr addr)
{
// Try to find a matching address based table of instructions.
DecodePage *page = decodePages.findPage(addr);
if (!page) {
// Nothing was found, so create a new one.
page = new DecodePage;
decodePages.addPage(addr, page);
}
// Use the table to decode the instruction. It will fall back to other
// mechanisms if it needs to.
return page->decode(mach_inst, addr, instMap);
}
};
#endif // __CPU_DECODE_CACHE_HH__
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