redop.h

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/*
 * Copyright 2025 Stanford University, NVIDIA Corporation
 * SPDX-License-Identifier: Apache-2.0
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
 
// reduction ops for Realm
 
#ifndef REALM_REDOP_H
#define REALM_REDOP_H
 
#include "realm/realm_config.h"
 
#ifdef REALM_USE_CUDA
#include "realm/cuda/cuda_redop.h"
#endif
 
#ifdef REALM_USE_HIP
#include "realm/hip/hip_redop.h"
#endif
 
#include <cstddef>
#include <type_traits>
 
namespace Realm {
 
  // a reduction op needs to look like this
#ifdef NOT_REALLY_CODE
  class MyReductionOp {
  public:
    typedef int LHS;
    typedef int RHS;
 
    void apply(LHS &lhs, RHS rhs) const;
 
    // both of these are optional
    static const RHS identity;
    void fold(RHS &rhs1, RHS rhs2) const;
  };
#endif
 
  template <typename REDOP>
  struct ReductionOp;
 
  struct ReductionOpUntyped {
    size_t sizeof_this; // includes any identity val or user data after struct
    size_t sizeof_lhs;
    size_t sizeof_rhs;
    size_t sizeof_userdata; // extra data supplied to apply/fold
    void *identity;         // if non-null, points into same object
    void *userdata;         // if non-null, points into same object
 
    // CPU apply/fold functions - tolerate strided src/dst
    void (*cpu_apply_excl_fn)(void *lhs_ptr, size_t lhs_stride, const void *rhs_ptr,
                              size_t rhs_stride, size_t count, const void *userdata);
    void (*cpu_apply_nonexcl_fn)(void *lhs_ptr, size_t lhs_stride, const void *rhs_ptr,
                                 size_t rhs_stride, size_t count, const void *userdata);
    void (*cpu_fold_excl_fn)(void *rhs1_ptr, size_t rhs1_stride, const void *rhs2_ptr,
                             size_t rhs2_stride, size_t count, const void *userdata);
    void (*cpu_fold_nonexcl_fn)(void *rhs1_ptr, size_t rhs1_stride, const void *rhs2_ptr,
                                size_t rhs2_stride, size_t count, const void *userdata);
 
#ifdef REALM_USE_CUDA
    // CUDA kernels for apply/fold - these are not actually the functions,
    //  but just information (e.g. host wrapper fnptr) that can be used
    //  to look up the actual kernels
    void *cuda_apply_excl_fn, *cuda_apply_nonexcl_fn;
    void *cuda_fold_excl_fn, *cuda_fold_nonexcl_fn;
 
    // These function pointers make the connection to the app's runtime
    // instance in order to properly translate and capture the correct
    // function to launch.
    // The runtime function pointer to launch these shadow symbols
    void *cudaLaunchKernel_fn;
    // The runtime function pointer to translate the host shadow symbol to a driver
    // function
    void *cudaGetFuncBySymbol_fn;
#endif
#ifdef REALM_USE_HIP
    // HIP kernels for apply/fold - these are not actually the functions,
    //  but just information (e.g. host wrapper fnptr) that can be used
    //  to look up the actual kernels
    void *hip_apply_excl_fn, *hip_apply_nonexcl_fn;
    void *hip_fold_excl_fn, *hip_fold_nonexcl_fn;
#endif
 
    ReductionOpUntyped()
      : sizeof_this(sizeof(ReductionOpUntyped))
      , sizeof_lhs(0)
      , sizeof_rhs(0)
      , sizeof_userdata(0)
      , identity(0)
      , userdata(0)
      , cpu_apply_excl_fn(0)
      , cpu_apply_nonexcl_fn(0)
      , cpu_fold_excl_fn(0)
      , cpu_fold_nonexcl_fn(0)
#ifdef REALM_USE_CUDA
      , cuda_apply_excl_fn(0)
      , cuda_apply_nonexcl_fn(0)
      , cuda_fold_excl_fn(0)
      , cuda_fold_nonexcl_fn(0)
      , cudaLaunchKernel_fn(0)
      , cudaGetFuncBySymbol_fn(0)
#endif
#ifdef REALM_USE_HIP
      , hip_apply_excl_fn(0)
      , hip_apply_nonexcl_fn(0)
      , hip_fold_excl_fn(0)
      , hip_fold_nonexcl_fn(0)
#endif
    {}
 
    template <class REDOP>
    static ReductionOpUntyped *create_reduction_op(void)
    {
      // reduction ops are allowed to use helper constructors, but are
      //  type-erased inside of realm, so must be trivially copyable and
      //  trivially destructible (we will use malloc/memcpy/free instead
      //  of new/delete)
      // FIXME:
      // TODO:
      // Re-enable when the examples used in legion CI are fixed.
#if 0
        static_assert(std::is_trivially_copyable<ReductionOp<REDOP>>::value &&
                          std::is_trivially_destructible<ReductionOp<REDOP>>::value,
                      "ReductionOp<REDOP> must be trivially copyable/destructible");
#endif
      void *ptr = malloc(sizeof(ReductionOp<REDOP>));
      if(ptr) {
        ReductionOpUntyped *redop = new(ptr) ReductionOp<REDOP>;
        return redop;
      } else
        return nullptr;
    }
 
    static ReductionOpUntyped *clone_reduction_op(const ReductionOpUntyped *redop);
  };
 
  namespace ReductionKernels {
    template <typename REDOP, bool EXCL>
    void cpu_apply_wrapper(void *lhs_ptr, size_t lhs_stride, const void *rhs_ptr,
                           size_t rhs_stride, size_t count, const void *userdata)
    {
      const REDOP *redop = static_cast<const REDOP *>(userdata);
      for(size_t i = 0; i < count; i++) {
        redop->template apply<EXCL>(*static_cast<typename REDOP::LHS *>(lhs_ptr),
                                    *static_cast<const typename REDOP::RHS *>(rhs_ptr));
        lhs_ptr = static_cast<char *>(lhs_ptr) + lhs_stride;
        rhs_ptr = static_cast<const char *>(rhs_ptr) + rhs_stride;
      }
    }
 
    template <typename REDOP, bool EXCL>
    void cpu_fold_wrapper(void *rhs1_ptr, size_t rhs1_stride, const void *rhs2_ptr,
                          size_t rhs2_stride, size_t count, const void *userdata)
    {
      const REDOP *redop = static_cast<const REDOP *>(userdata);
      for(size_t i = 0; i < count; i++) {
        redop->template fold<EXCL>(*static_cast<typename REDOP::RHS *>(rhs1_ptr),
                                   *static_cast<const typename REDOP::RHS *>(rhs2_ptr));
        rhs1_ptr = static_cast<char *>(rhs1_ptr) + rhs1_stride;
        rhs2_ptr = static_cast<const char *>(rhs2_ptr) + rhs2_stride;
      }
    }
  }; // namespace ReductionKernels
 
#if defined(REALM_USE_CUDA) && defined(__CUDACC__)
  // with a cuda-capable compiler, we'll automatically add cuda reduction
  //  kernels if the REDOP class defines has_cuda_reductions AND it's true
  // this requires a bunch of SFINAE template-fu
  template <typename T>
  struct HasHasCudaReductions {
    struct YES {
      char dummy[1];
    };
    struct NO {
      char dummy[2];
    };
    struct AltnerativeDefinition {
      static const bool has_cuda_reductions = false;
    };
    template <typename T2>
    struct Combined : public T2, public AltnerativeDefinition {};
    template <typename T2, T2>
    struct CheckAmbiguous {};
    template <typename T2>
    static NO
    has_member(CheckAmbiguous<const bool *, &Combined<T2>::has_cuda_reductions> *);
    template <typename T2>
    static YES has_member(...);
    const static bool value = sizeof(has_member<T>(0)) == sizeof(YES);
  };
 
  template <typename T, bool OK>
  struct MaybeAddCudaReductions;
  template <typename T>
  struct MaybeAddCudaReductions<T, false> {
    static void if_member_exists(ReductionOpUntyped *redop){};
    static void if_member_is_true(ReductionOpUntyped *redop){};
  };
  template <typename T>
  struct MaybeAddCudaReductions<T, true> {
    static void if_member_exists(ReductionOpUntyped *redop)
    {
      MaybeAddCudaReductions<T, T::has_cuda_reductions>::if_member_is_true(redop);
    }
    static void if_member_is_true(ReductionOpUntyped *redop)
    {
      Cuda::add_cuda_redop_kernels<T>(redop);
    }
  };
#endif
 
#if defined(REALM_USE_HIP) && (defined(__CUDACC__) || defined(__HIPCC__))
  // with a hip-capable compiler, we'll automatically add hip reduction
  //  kernels if the REDOP class defines has_hip_reductions AND it's true
  // this requires a bunch of SFINAE template-fu
  template <typename T>
  struct HasHasHipReductions {
    struct YES {
      char dummy[1];
    };
    struct NO {
      char dummy[2];
    };
    struct AltnerativeDefinition {
      static const bool has_hip_reductions = false;
    };
    template <typename T2>
    struct Combined : public T2, public AltnerativeDefinition {};
    template <typename T2, T2>
    struct CheckAmbiguous {};
    template <typename T2>
    static NO
    has_member(CheckAmbiguous<const bool *, &Combined<T2>::has_hip_reductions> *);
    template <typename T2>
    static YES has_member(...);
    const static bool value = sizeof(has_member<T>(0)) == sizeof(YES);
  };
 
  template <typename T, bool OK>
  struct MaybeAddHipReductions;
  template <typename T>
  struct MaybeAddHipReductions<T, false> {
    static void if_member_exists(ReductionOpUntyped *redop){};
    static void if_member_is_true(ReductionOpUntyped *redop){};
  };
  template <typename T>
  struct MaybeAddHipReductions<T, true> {
    static void if_member_exists(ReductionOpUntyped *redop)
    {
      MaybeAddHipReductions<T, T::has_hip_reductions>::if_member_is_true(redop);
    }
    static void if_member_is_true(ReductionOpUntyped *redop)
    {
      Hip::add_hip_redop_kernels<T>(redop);
    }
  };
#endif
 
  template <typename REDOP>
  struct ReductionOp : public ReductionOpUntyped {
    // tacked on to end of ReductionOpUntyped struct
    typename REDOP::RHS identity_val;
    REDOP userdata_val;
 
    ReductionOp()
      : identity_val(REDOP::identity)
      , userdata_val()
    {
      sizeof_this = sizeof(ReductionOp<REDOP>);
      sizeof_lhs = sizeof(typename REDOP::LHS);
      sizeof_rhs = sizeof(typename REDOP::RHS);
      sizeof_userdata = sizeof(REDOP);
      identity = &identity_val;
      userdata = &userdata_val;
      cpu_apply_excl_fn = &ReductionKernels::cpu_apply_wrapper<REDOP, true>;
      cpu_apply_nonexcl_fn = &ReductionKernels::cpu_apply_wrapper<REDOP, false>;
      cpu_fold_excl_fn = &ReductionKernels::cpu_fold_wrapper<REDOP, true>;
      cpu_fold_nonexcl_fn = &ReductionKernels::cpu_fold_wrapper<REDOP, false>;
#if defined(REALM_USE_CUDA) && defined(__CUDACC__)
      // if REDOP defines/sets 'has_cuda_reductions' to true, try to
      //  automatically build wrappers for apply_cuda<> and fold_cuda<>
      MaybeAddCudaReductions<REDOP, HasHasCudaReductions<REDOP>::value>::if_member_exists(
          this);
#endif
#if defined(REALM_USE_HIP) && (defined(__CUDACC__) || defined(__HIPCC__))
      // if REDOP defines/sets 'has_hip_reductions' to true, try to
      //  automatically build wrappers for apply_hip<> and fold_hip<>
      MaybeAddHipReductions<REDOP, HasHasHipReductions<REDOP>::value>::if_member_exists(
          this);
#endif
    }
 
  protected:
  };
 
}; // namespace Realm
 
  // include "redop.inl"
 
#endif // ifndef REALM_REDOP_H