warp_reduce_shfl.cuh

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/******************************************************************************
 * Copyright (c) 2011, Duane Merrill.  All rights reserved.
 * Copyright (c) 2011-2018, NVIDIA CORPORATION.  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.
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 *       names of its contributors may be used to endorse or promote products
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#pragma once

#include "../../thread/thread_operators.cuh"
#include "../../util_ptx.cuh"
#include "../../util_type.cuh"
#include "../../util_macro.cuh"
#include "../../util_namespace.cuh"

CUB_NS_PREFIX

namespace cub {


template <
    typename    T,                      
    int         LOGICAL_WARP_THREADS,   
    int         PTX_ARCH>               
struct WarpReduceShfl
{
    //---------------------------------------------------------------------
    // Constants and type definitions
    //---------------------------------------------------------------------

    enum
    {
        IS_ARCH_WARP = (LOGICAL_WARP_THREADS == CUB_WARP_THREADS(PTX_ARCH)),

        STEPS = Log2<LOGICAL_WARP_THREADS>::VALUE,

        LOGICAL_WARPS = CUB_WARP_THREADS(PTX_ARCH) / LOGICAL_WARP_THREADS,

        SHFL_C = (CUB_WARP_THREADS(PTX_ARCH) - LOGICAL_WARP_THREADS) << 8

    };

    template <typename S>
    struct IsInteger
    {
        enum {
            IS_SMALL_UNSIGNED = (Traits<S>::CATEGORY == UNSIGNED_INTEGER) && (sizeof(S) <= sizeof(unsigned int))
        };
    };


    typedef NullType TempStorage;


    //---------------------------------------------------------------------
    // Thread fields
    //---------------------------------------------------------------------

    unsigned int lane_id;

    unsigned int warp_id;

    unsigned int member_mask;


    //---------------------------------------------------------------------
    // Construction
    //---------------------------------------------------------------------

    __device__ __forceinline__ WarpReduceShfl(
        TempStorage &/*temp_storage*/)
    {
        lane_id = LaneId();
        warp_id = 0;
        member_mask = 0xffffffffu >> (CUB_WARP_THREADS(PTX_ARCH) - LOGICAL_WARP_THREADS);

        if (!IS_ARCH_WARP)
        {
            warp_id = lane_id / LOGICAL_WARP_THREADS;
            lane_id = lane_id % LOGICAL_WARP_THREADS;
            member_mask = member_mask << (warp_id * LOGICAL_WARP_THREADS);
        }
    }


    //---------------------------------------------------------------------
    // Reduction steps
    //---------------------------------------------------------------------

    __device__ __forceinline__ unsigned int ReduceStep(
        unsigned int    input,              
        cub::Sum        /*reduction_op*/,   
        int             last_lane,          
        int             offset)             
    {
        unsigned int output;
        int shfl_c = last_lane | SHFL_C;   // Shuffle control (mask and last_lane)

        // Use predicate set from SHFL to guard against invalid peers
#ifdef CUB_USE_COOPERATIVE_GROUPS
        asm volatile(
            "{"
            "  .reg .u32 r0;"
            "  .reg .pred p;"
            "  shfl.sync.down.b32 r0|p, %1, %2, %3, %5;"
            "  @p add.u32 r0, r0, %4;"
            "  mov.u32 %0, r0;"
            "}"
            : "=r"(output) : "r"(input), "r"(offset), "r"(shfl_c), "r"(input), "r"(member_mask));
#else
        asm volatile(
            "{"
            "  .reg .u32 r0;"
            "  .reg .pred p;"
            "  shfl.down.b32 r0|p, %1, %2, %3;"
            "  @p add.u32 r0, r0, %4;"
            "  mov.u32 %0, r0;"
            "}"
            : "=r"(output) : "r"(input), "r"(offset), "r"(shfl_c), "r"(input));
#endif

        return output;
    }


    __device__ __forceinline__ float ReduceStep(
        float           input,              
        cub::Sum        /*reduction_op*/,   
        int             last_lane,          
        int             offset)             
    {
        float output;
        int shfl_c = last_lane | SHFL_C;   // Shuffle control (mask and last_lane)

        // Use predicate set from SHFL to guard against invalid peers
#ifdef CUB_USE_COOPERATIVE_GROUPS
        asm volatile(
            "{"
            "  .reg .f32 r0;"
            "  .reg .pred p;"
            "  shfl.sync.down.b32 r0|p, %1, %2, %3, %5;"
            "  @p add.f32 r0, r0, %4;"
            "  mov.f32 %0, r0;"
            "}"
            : "=f"(output) : "f"(input), "r"(offset), "r"(shfl_c), "f"(input), "r"(member_mask));
#else
        asm volatile(
            "{"
            "  .reg .f32 r0;"
            "  .reg .pred p;"
            "  shfl.down.b32 r0|p, %1, %2, %3;"
            "  @p add.f32 r0, r0, %4;"
            "  mov.f32 %0, r0;"
            "}"
            : "=f"(output) : "f"(input), "r"(offset), "r"(shfl_c), "f"(input));
#endif

        return output;
    }


    __device__ __forceinline__ unsigned long long ReduceStep(
        unsigned long long  input,              
        cub::Sum            /*reduction_op*/,   
        int                 last_lane,          
        int                 offset)             
    {
        unsigned long long output;
        int shfl_c = last_lane | SHFL_C;   // Shuffle control (mask and last_lane)

#ifdef CUB_USE_COOPERATIVE_GROUPS
        asm volatile(
            "{"
            "  .reg .u32 lo;"
            "  .reg .u32 hi;"
            "  .reg .pred p;"
            "  mov.b64 {lo, hi}, %1;"
            "  shfl.sync.down.b32 lo|p, lo, %2, %3, %4;"
            "  shfl.sync.down.b32 hi|p, hi, %2, %3, %4;"
            "  mov.b64 %0, {lo, hi};"
            "  @p add.u64 %0, %0, %1;"
            "}"
            : "=l"(output) : "l"(input), "r"(offset), "r"(shfl_c), "r"(member_mask));
#else
        asm volatile(
            "{"
            "  .reg .u32 lo;"
            "  .reg .u32 hi;"
            "  .reg .pred p;"
            "  mov.b64 {lo, hi}, %1;"
            "  shfl.down.b32 lo|p, lo, %2, %3;"
            "  shfl.down.b32 hi|p, hi, %2, %3;"
            "  mov.b64 %0, {lo, hi};"
            "  @p add.u64 %0, %0, %1;"
            "}"
            : "=l"(output) : "l"(input), "r"(offset), "r"(shfl_c));
#endif

        return output;
    }


    __device__ __forceinline__ long long ReduceStep(
        long long           input,              
        cub::Sum            /*reduction_op*/,   
        int                 last_lane,          
        int                 offset)             
    {
        long long output;
        int shfl_c = last_lane | SHFL_C;   // Shuffle control (mask and last_lane)

        // Use predicate set from SHFL to guard against invalid peers
#ifdef CUB_USE_COOPERATIVE_GROUPS
        asm volatile(
            "{"
            "  .reg .u32 lo;"
            "  .reg .u32 hi;"
            "  .reg .pred p;"
            "  mov.b64 {lo, hi}, %1;"
            "  shfl.sync.down.b32 lo|p, lo, %2, %3, %4;"
            "  shfl.sync.down.b32 hi|p, hi, %2, %3, %4;"
            "  mov.b64 %0, {lo, hi};"
            "  @p add.s64 %0, %0, %1;"
            "}"
            : "=l"(output) : "l"(input), "r"(offset), "r"(shfl_c), "r"(member_mask));
#else
        asm volatile(
            "{"
            "  .reg .u32 lo;"
            "  .reg .u32 hi;"
            "  .reg .pred p;"
            "  mov.b64 {lo, hi}, %1;"
            "  shfl.down.b32 lo|p, lo, %2, %3;"
            "  shfl.down.b32 hi|p, hi, %2, %3;"
            "  mov.b64 %0, {lo, hi};"
            "  @p add.s64 %0, %0, %1;"
            "}"
            : "=l"(output) : "l"(input), "r"(offset), "r"(shfl_c));
#endif

        return output;
    }


    __device__ __forceinline__ double ReduceStep(
        double              input,              
        cub::Sum            /*reduction_op*/,   
        int                 last_lane,          
        int                 offset)             
    {
        double output;
        int shfl_c = last_lane | SHFL_C;   // Shuffle control (mask and last_lane)

        // Use predicate set from SHFL to guard against invalid peers
#ifdef CUB_USE_COOPERATIVE_GROUPS
        asm volatile(
            "{"
            "  .reg .u32 lo;"
            "  .reg .u32 hi;"
            "  .reg .pred p;"
            "  .reg .f64 r0;"
            "  mov.b64 %0, %1;"
            "  mov.b64 {lo, hi}, %1;"
            "  shfl.sync.down.b32 lo|p, lo, %2, %3, %4;"
            "  shfl.sync.down.b32 hi|p, hi, %2, %3, %4;"
            "  mov.b64 r0, {lo, hi};"
            "  @p add.f64 %0, %0, r0;"
            "}"
            : "=d"(output) : "d"(input), "r"(offset), "r"(shfl_c), "r"(member_mask));
#else
        asm volatile(
            "{"
            "  .reg .u32 lo;"
            "  .reg .u32 hi;"
            "  .reg .pred p;"
            "  .reg .f64 r0;"
            "  mov.b64 %0, %1;"
            "  mov.b64 {lo, hi}, %1;"
            "  shfl.down.b32 lo|p, lo, %2, %3;"
            "  shfl.down.b32 hi|p, hi, %2, %3;"
            "  mov.b64 r0, {lo, hi};"
            "  @p add.f64 %0, %0, r0;"
            "}"
            : "=d"(output) : "d"(input), "r"(offset), "r"(shfl_c));
#endif

        return output;
    }


    template <typename ValueT, typename KeyT>
    __device__ __forceinline__ KeyValuePair<KeyT, ValueT> ReduceStep(
        KeyValuePair<KeyT, ValueT>                  input,              
        SwizzleScanOp<ReduceByKeyOp<cub::Sum> >     /*reduction_op*/,   
        int                                         last_lane,          
        int                                         offset)             
    {
        KeyValuePair<KeyT, ValueT> output;

        KeyT other_key = ShuffleDown<LOGICAL_WARP_THREADS>(input.key, offset, last_lane, member_mask);
        
        output.key = input.key;
        output.value = ReduceStep(
            input.value, 
            cub::Sum(), 
            last_lane, 
            offset, 
            Int2Type<IsInteger<ValueT>::IS_SMALL_UNSIGNED>());

        if (input.key != other_key)
            output.value = input.value;

        return output;
    }



    template <typename ValueT, typename OffsetT>
    __device__ __forceinline__ KeyValuePair<OffsetT, ValueT> ReduceStep(
        KeyValuePair<OffsetT, ValueT>                 input,              
        SwizzleScanOp<ReduceBySegmentOp<cub::Sum> >   /*reduction_op*/,   
        int                                           last_lane,          
        int                                           offset)             
    {
        KeyValuePair<OffsetT, ValueT> output;

        output.value = ReduceStep(input.value, cub::Sum(), last_lane, offset, Int2Type<IsInteger<ValueT>::IS_SMALL_UNSIGNED>());
        output.key = ReduceStep(input.key, cub::Sum(), last_lane, offset, Int2Type<IsInteger<OffsetT>::IS_SMALL_UNSIGNED>());

        if (input.key > 0)
            output.value = input.value;

        return output;
    }


    template <typename _T, typename ReductionOp>
    __device__ __forceinline__ _T ReduceStep(
        _T                  input,              
        ReductionOp         reduction_op,       
        int                 last_lane,          
        int                 offset)             
    {
        _T output = input;

        _T temp = ShuffleDown<LOGICAL_WARP_THREADS>(output, offset, last_lane, member_mask);

        // Perform reduction op if valid
        if (offset + lane_id <= last_lane)
            output = reduction_op(input, temp);

        return output;
    }


    template <typename _T, typename ReductionOp>
    __device__ __forceinline__ _T ReduceStep(
        _T              input,                  
        ReductionOp     reduction_op,           
        int             last_lane,              
        int             offset,                 
        Int2Type<true>  /*is_small_unsigned*/)  
    {
        return ReduceStep(input, reduction_op, last_lane, offset);
    }


    template <typename _T, typename ReductionOp>
    __device__ __forceinline__ _T ReduceStep(
        _T              input,                  
        ReductionOp     reduction_op,           
        int             last_lane,              
        int             offset,                 
        Int2Type<false> /*is_small_unsigned*/)  
    {
        return ReduceStep(input, reduction_op, last_lane, offset);
    }


    //---------------------------------------------------------------------
    // Templated inclusive scan iteration
    //---------------------------------------------------------------------

    template <typename ReductionOp, int STEP>
    __device__ __forceinline__ void ReduceStep(
        T&              input,              
        ReductionOp     reduction_op,       
        int             last_lane,          
        Int2Type<STEP>  /*step*/)
    {
        input = ReduceStep(input, reduction_op, last_lane, 1 << STEP, Int2Type<IsInteger<T>::IS_SMALL_UNSIGNED>());

        ReduceStep(input, reduction_op, last_lane, Int2Type<STEP + 1>());
    }

    template <typename ReductionOp>
    __device__ __forceinline__ void ReduceStep(
        T&              /*input*/,              
        ReductionOp     /*reduction_op*/,       
        int             /*last_lane*/,          
        Int2Type<STEPS> /*step*/)
    {}


    //---------------------------------------------------------------------
    // Reduction operations
    //---------------------------------------------------------------------

    template <
        bool            ALL_LANES_VALID,        
        typename        ReductionOp>
    __device__ __forceinline__ T Reduce(
        T               input,                  
        int             valid_items,            
        ReductionOp     reduction_op)           
    {
        int last_lane = (ALL_LANES_VALID) ?
                            LOGICAL_WARP_THREADS - 1 :
                            valid_items - 1;

        T output = input;

//        // Iterate reduction steps
//        #pragma unroll
//        for (int STEP = 0; STEP < STEPS; STEP++)
//        {
//            output = ReduceStep(output, reduction_op, last_lane, 1 << STEP, Int2Type<IsInteger<T>::IS_SMALL_UNSIGNED>());
//        }

        // Template-iterate reduction steps
        ReduceStep(output, reduction_op, last_lane, Int2Type<0>());

        return output;
    }


    template <
        bool            HEAD_SEGMENTED,     
        typename        FlagT,
        typename        ReductionOp>
    __device__ __forceinline__ T SegmentedReduce(
        T               input,              
        FlagT           flag,               
        ReductionOp     reduction_op)       
    {
        // Get the start flags for each thread in the warp.
        int warp_flags = WARP_BALLOT(flag, member_mask);

        // Convert to tail-segmented
        if (HEAD_SEGMENTED)
            warp_flags >>= 1;

        // Mask out the bits below the current thread
        warp_flags &= LaneMaskGe();

        // Mask of physical lanes outside the logical warp and convert to logical lanemask
        if (!IS_ARCH_WARP)
        {
            warp_flags = (warp_flags & member_mask) >> (warp_id * LOGICAL_WARP_THREADS);
        }

        // Mask in the last lane of logical warp
        warp_flags |= 1u << (LOGICAL_WARP_THREADS - 1);

        // Find the next set flag
        int last_lane = __clz(__brev(warp_flags));

        T output = input;

//        // Iterate reduction steps
//        #pragma unroll
//        for (int STEP = 0; STEP < STEPS; STEP++)
//        {
//            output = ReduceStep(output, reduction_op, last_lane, 1 << STEP, Int2Type<IsInteger<T>::IS_SMALL_UNSIGNED>());
//        }

        // Template-iterate reduction steps
        ReduceStep(output, reduction_op, last_lane, Int2Type<0>());

        return output;
    }
};


}               // CUB namespace
CUB_NS_POSTFIX  // Optional outer namespace(s)