src/cpu/o3/free_list.hh

/*
 * Copyright (c) 2016-2018 ARM Limited
 * All rights reserved
 *
 * The license below extends only to copyright in the software and shall
 * not be construed as granting a license to any other intellectual
 * property including but not limited to intellectual property relating
 * to a hardware implementation of the functionality of the software
 * licensed hereunder. You may use the software subject to the license
 * terms below provided that you ensure that this notice is replicated
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 * modified or unmodified, in source code or in binary form.
 *
 * Copyright (c) 2004-2005 The Regents of The University of Michigan
 * Copyright (c) 2013 Advanced Micro Devices, Inc.
 * All rights reserved.
 *
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 * 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
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 * neither the name of the copyright holders nor the names of its
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 * this software without specific prior written permission.
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#ifndef __CPU_O3_FREE_LIST_HH__
#define __CPU_O3_FREE_LIST_HH__

#include <algorithm>
#include <array>
#include <iostream>
#include <queue>

#include "base/logging.hh"
#include "base/trace.hh"
#include "cpu/o3/comm.hh"
#include "cpu/o3/regfile.hh"
#include "debug/FreeList.hh"

namespace gem5
{

namespace o3
{

class UnifiedRenameMap;

/**
 * Free list for a single class of registers (e.g., integer
 * or floating point).  Because the register class is implicitly
 * determined by the rename map instance being accessed, all
 * architectural register index parameters and values in this class
 * are relative (e.g., %fp2 is just index 2).
 */
class SimpleFreeList
{
  private:

    /** The actual free list */
    std::queue<PhysRegIdPtr> freeRegs;

  public:

    SimpleFreeList() {};

    /** Add a physical register to the free list */
    void addReg(PhysRegIdPtr reg) { freeRegs.push(reg); }

    /** Add physical registers to the free list */
    template<class InputIt>
    void
    addRegs(InputIt first, InputIt last) {
        std::for_each(first, last, [this](typename InputIt::value_type& reg) {
            freeRegs.push(&reg);
        });
    }

    /** Get the next available register from the free list */
    PhysRegIdPtr getReg()
    {
        assert(!freeRegs.empty());
        PhysRegIdPtr free_reg = freeRegs.front();
        freeRegs.pop();
        return free_reg;
    }

    /** Return the number of free registers on the list. */
    unsigned numFreeRegs() const { return freeRegs.size(); }

    /** True iff there are free registers on the list. */
    bool hasFreeRegs() const { return !freeRegs.empty(); }
};


/**
 * FreeList class that simply holds the list of free integer and floating
 * point registers.  Can request for a free register of either type, and
 * also send back free registers of either type.  This is a very simple
 * class, but it should be sufficient for most implementations.  Like all
 * other classes, it assumes that the indices for the floating point
 * registers starts after the integer registers end.  Hence the variable
 * numPhysicalIntRegs is logically equivalent to the baseFP dependency.
 * Note that while this most likely should be called FreeList, the name
 * "FreeList" is used in a typedef within the CPU Policy, and therefore no
 * class can be named simply "FreeList".
 * @todo: Give a better name to the base FP dependency.
 */
class UnifiedFreeList
{
  private:

    /** The object name, for DPRINTF.  We have to declare this
     *  explicitly because Scoreboard is not a SimObject. */
    const std::string _name;

    std::array<SimpleFreeList, CCRegClass + 1> freeLists;

    /**
     * The register file object is used only to distinguish integer
     * from floating-point physical register indices.
     */
    PhysRegFile *regFile;

    /*
     * We give UnifiedRenameMap internal access so it can get at the
     * internal per-class free lists and associate those with its
     * per-class rename maps. See UnifiedRenameMap::init().
     */
    friend class UnifiedRenameMap;

  public:
    /** Constructs a free list.
     *  @param _numPhysicalIntRegs Number of physical integer registers.
     *  @param reservedIntRegs Number of integer registers already
     *                         used by initial mappings.
     *  @param _numPhysicalFloatRegs Number of physical fp registers.
     *  @param reservedFloatRegs Number of fp registers already
     *                           used by initial mappings.
     */
    UnifiedFreeList(const std::string &_my_name, PhysRegFile *_regFile);

    /** Gives the name of the freelist. */
    std::string name() const { return _name; };

    /** Gets a free register of type type. */
    PhysRegIdPtr getReg(RegClassType type) { return freeLists[type].getReg(); }

    /** Adds a register back to the free list. */
    template<class InputIt>
    void
    addRegs(InputIt first, InputIt last)
    {
        std::for_each(first, last, [this](auto &reg) { addReg(&reg); });
    }

    /** Adds a register back to the free list. */
    void
    addReg(PhysRegIdPtr freed_reg)
    {
        freeLists[freed_reg->classValue()].addReg(freed_reg);
    }

    /** Checks if there are any free registers of type type. */
    bool
    hasFreeRegs(RegClassType type) const
    {
        return freeLists[type].hasFreeRegs();
    }

    /** Returns the number of free registers of type type. */
    unsigned
    numFreeRegs(RegClassType type) const
    {
        return freeLists[type].numFreeRegs();
    }
};

} // namespace o3
} // namespace gem5

#endif // __CPU_O3_FREE_LIST_HH__