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/*
* Copyright (c) 2004-2005 The Regents of The University of Michigan
* 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: Kevin Lim
*/
#ifndef __CPU_O3_BTB_HH__
#define __CPU_O3_BTB_HH__
#include "base/misc.hh"
#include "base/types.hh"
class DefaultBTB
{
private:
struct BTBEntry
{
BTBEntry()
: tag(0), target(0), valid(false)
{
}
/** The entry's tag. */
Addr tag;
/** The entry's target. */
Addr target;
/** The entry's thread id. */
ThreadID tid;
/** Whether or not the entry is valid. */
bool valid;
};
public:
/** Creates a BTB with the given number of entries, number of bits per
* tag, and instruction offset amount.
* @param numEntries Number of entries for the BTB.
* @param tagBits Number of bits for each tag in the BTB.
* @param instShiftAmt Offset amount for instructions to ignore alignment.
*/
DefaultBTB(unsigned numEntries, unsigned tagBits,
unsigned instShiftAmt);
void reset();
/** Looks up an address in the BTB. Must call valid() first on the address.
* @param inst_PC The address of the branch to look up.
* @param tid The thread id.
* @return Returns the target of the branch.
*/
Addr lookup(const Addr &inst_PC, ThreadID tid);
/** Checks if a branch is in the BTB.
* @param inst_PC The address of the branch to look up.
* @param tid The thread id.
* @return Whether or not the branch exists in the BTB.
*/
bool valid(const Addr &inst_PC, ThreadID tid);
/** Updates the BTB with the target of a branch.
* @param inst_PC The address of the branch being updated.
* @param target_PC The target address of the branch.
* @param tid The thread id.
*/
void update(const Addr &inst_PC, const Addr &target_PC,
ThreadID tid);
private:
/** Returns the index into the BTB, based on the branch's PC.
* @param inst_PC The branch to look up.
* @return Returns the index into the BTB.
*/
inline unsigned getIndex(const Addr &inst_PC);
/** Returns the tag bits of a given address.
* @param inst_PC The branch's address.
* @return Returns the tag bits.
*/
inline Addr getTag(const Addr &inst_PC);
/** The actual BTB. */
std::vector<BTBEntry> btb;
/** The number of entries in the BTB. */
unsigned numEntries;
/** The index mask. */
unsigned idxMask;
/** The number of tag bits per entry. */
unsigned tagBits;
/** The tag mask. */
unsigned tagMask;
/** Number of bits to shift PC when calculating index. */
unsigned instShiftAmt;
/** Number of bits to shift PC when calculating tag. */
unsigned tagShiftAmt;
};
#endif // __CPU_O3_BTB_HH__
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