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#ifndef __nanojit_RegAlloc__
#define __nanojit_RegAlloc__


namespace nanojit
{
    inline RegisterMask rmask(Register r)
    {
        return RegisterMask(1) << r;
    }

    class RegAlloc
    {
    public:
        RegAlloc()
        {
            clear();
        }

        void clear()
        {
            VMPI_memset(this, 0, sizeof(*this));
        }

        bool isFree(Register r)
        {
            NanoAssert(r != UnknownReg);
            return (free & rmask(r)) != 0;
        }

        void addFree(Register r)
        {
            NanoAssert(!isFree(r));
            free |= rmask(r);
        }

        void removeFree(Register r)
        {
            NanoAssert(isFree(r));
            free &= ~rmask(r);
        }

        void addActive(Register r, LIns* v)
        {
            //  Count++;
            NanoAssert(v);
            NanoAssert(r != UnknownReg);
            NanoAssert(active[r] == NULL);
            active[r] = v;
            useActive(r);
        }

        void useActive(Register r)
        {
            NanoAssert(r != UnknownReg);
            NanoAssert(active[r] != NULL);
            usepri[r] = priority++;
        }

        void removeActive(Register r)
        {
            //registerReleaseCount++;
            NanoAssert(r != UnknownReg);
            NanoAssert(active[r] != NULL);

            // remove the given register from the active list
            active[r] = NULL;
        }

        void retire(Register r)
        {
            NanoAssert(r != UnknownReg);
            NanoAssert(active[r] != NULL);
            active[r] = NULL;
            free |= rmask(r);
        }

        int32_t getPriority(Register r) {
            NanoAssert(r != UnknownReg && active[r]);
            return usepri[r];
        }

        LIns* getActive(Register r) {
            NanoAssert(r != UnknownReg);
            return active[r];
        }

        debug_only( uint32_t    countActive(); )
        debug_only( bool        isConsistent(Register r, LIns* v); )
        debug_only( RegisterMask managed; )     // the registers managed by the register allocator

        // Some basics:
        //
        // - 'active' indicates which registers are active at a particular
        //   point, and for each active register, which instruction
        //   defines the value it holds.  At the start of register
        //   allocation no registers are active.
        //
        // - 'free' indicates which registers are free at a particular point
        //   and thus available for use.  At the start of register
        //   allocation most registers are free;  those that are not
        //   aren't available for general use, e.g. the stack pointer and
        //   frame pointer registers.  
        //
        // - 'managed' is exactly this list of initially free registers,
        //   ie. the registers managed by the register allocator.
        //
        // - Each LIns has a "reservation" which includes a register value,
        //   'reg'.  Combined with 'active', this provides a two-way
        //   mapping between registers and LIR instructions.
        //
        // - Invariant 1: each register must be in exactly one of the
        //   following states at all times:  unmanaged, free, or active.
        //   In terms of the relevant fields:
        //
        //   * A register in 'managed' must be in 'active' or 'free' but
        //     not both.
        //
        //   * A register not in 'managed' must be in neither 'active' nor
        //     'free'.
        //
        // - Invariant 2: the two-way mapping between active registers and
        //   their defining instructions must always hold in both
        //   directions and be unambiguous.  More specifically:
        //
        //   * An LIns can appear at most once in 'active'.
        //
        //   * An LIns named by 'active[R]' must have an in-use
        //     reservation that names R.  
        //
        //   * And vice versa:  an LIns with an in-use reservation that
        //     names R must be named by 'active[R]'.  
        //
        //   * If an LIns's reservation names 'UnknownReg' then LIns
        //     should not be in 'active'.
        //
        LIns*           active[LastReg + 1];    // active[r] = LIns that defines r
        int32_t         usepri[LastReg + 1];    // used priority. lower = more likely to spill.
        RegisterMask    free;
        int32_t         priority;

        DECLARE_PLATFORM_REGALLOC()
    };
}
#endif // __nanojit_RegAlloc__
