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Reduce.h
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Reduce.h
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#pragma once
#include <ATen/native/cpu/Loops.h>
#include <ATen/Parallel.h>
#include <c10/util/TypeList.h>
#include <sstream>
namespace at { namespace native { namespace {
using namespace vec256;
#define VEC_LOOP_HEADER(func_t, data) \
using scalar_t = typename function_traits<func_t>::result_type; \
using Vec = Vec256<scalar_t>; \
char* out_ptr = data[0]; \
(void) out_ptr;
// reduction that is contiguous over the input in dim 0
template <typename traits>
static inline bool is_contiguous_reduction(const int64_t* strides) {
return strides[0] == 0 &&
strides[1] == sizeof(typename traits::arg2_t);
}
// reduction that is contiguous over the input in dim 1
template <typename traits>
static inline bool is_outer_reduction(const int64_t* strides) {
return strides[0] == 0 &&
strides[2] == sizeof(typename traits::result_type) &&
strides[3] == sizeof(typename traits::arg2_t);
}
template <typename func_t, typename vec_func_t>
static inline void reduction128(char** data, int64_t n, int64_t stride, func_t op, vec_func_t vop, bool reduce) {
VEC_LOOP_HEADER(func_t, data)
const char* in1_ptr = data[1];
Vec acc[4];
for (int j = 0; j < 4; j++) {
acc[j] = Vec::loadu(in1_ptr + j * Vec::size() * sizeof(scalar_t));
}
for (int64_t i = 1; i < n; i++) {
const char* ptr = in1_ptr + stride * i;
acc[0] = vop(acc[0], Vec::loadu(ptr + (0 * Vec::size() * sizeof(scalar_t))));
acc[1] = vop(acc[1], Vec::loadu(ptr + (1 * Vec::size() * sizeof(scalar_t))));
acc[2] = vop(acc[2], Vec::loadu(ptr + (2 * Vec::size() * sizeof(scalar_t))));
acc[3] = vop(acc[3], Vec::loadu(ptr + (3 * Vec::size() * sizeof(scalar_t))));
}
if (reduce) {
scalar_t buffer[Vec::size()];
acc[0] = vop(vop(acc[0], acc[1]), vop(acc[2], acc[3]));
acc[0].store(buffer);
for (int j = 1; j < Vec::size(); j++) {
buffer[0] = op(buffer[0], buffer[j]);
}
auto dst = (scalar_t*)out_ptr;
*dst = op(*dst, buffer[0]);
} else {
for (int j = 0; j < 4; j++) {
auto dst = out_ptr + j * Vec::size() * sizeof(scalar_t);
acc[j] = vop(acc[j], Vec::loadu(dst));
acc[j].store(dst);
}
}
}
template <typename F>
static inline void UNARY_OUTER_LOOP(char* data[2], const int64_t strides[2], int64_t n, F f) {
for (int j = 0; j < n; j++) {
f();
data[0] += strides[0];
data[1] += strides[1];
}
}
// computes the reduction out = op(out, in)
template <typename func_t, typename vec_func_t>
static inline void vectorized_inner_reduction(char** data, int64_t n, func_t op, vec_func_t vop) {
VEC_LOOP_HEADER(func_t, data)
int64_t vector_stride = 4 * Vec::size() * sizeof(scalar_t);
int64_t count = n / (4 * Vec::size());
if (count > 0) {
reduction128(data, count, vector_stride, op, vop, /*reduce=*/true);
}
char* ptrs[3] = { data[0], data[0], data[1] };
int64_t strides[] = { 0, 0, sizeof(scalar_t) };
basic_loop(ptrs, strides, count * 4 * Vec::size(), n, op);
}
// computes the reduction out = op(out, in)
template <typename func_t, typename vec_func_t>
static inline void vectorized_outer_reduction(char** data, int64_t inner_stride, int64_t size0, int64_t size1, func_t op, vec_func_t vop) {
VEC_LOOP_HEADER(func_t, data)
// reduce down each column of 4 * Vec::size() elements (128 bytes)
int64_t outer_stride[2] = { 128, 128 };
UNARY_OUTER_LOOP(data, outer_stride, size1 / (4 * Vec::size()), [&] {
reduction128(data, size0, inner_stride, op, vop, /*reduce=*/false);
});
// reduce down the remaining columns
int64_t step[] = { sizeof(scalar_t), sizeof(scalar_t) };
int64_t remaining = size1 % (4 * Vec::size());
UNARY_OUTER_LOOP(data, step, remaining, [&] {
char* ptrs[3] = { data[0], data[0], data[1] };
int64_t strides[] = { 0, 0, inner_stride };
basic_loop(ptrs, strides, 0, size0, op);
});
}
template<typename traits, typename res_t>
static void set_result(const int index, const res_t result, const TensorIterator &iter, const int num_outputs) {
// static_assert(std::is_same<res_t, typename traits::arg2_t>::value, "data types must match");
if (index < num_outputs) {
char *out = (char *) iter.data_ptr(index);
*(res_t *) out = result;
}
}
template<typename traits, typename res_t>
static void set_results(const res_t result, const TensorIterator &iter, const int num_outputs) {
AT_ASSERT(num_outputs == 1);
set_result<traits>(0, result, iter, num_outputs);
}
template<typename traits, std::size_t i = 0, typename... tuple_t>
static inline typename std::enable_if<i == sizeof...(tuple_t), std::size_t>::type
for_each_in_tuple(const std::tuple<tuple_t...>& t, const TensorIterator &iter, const int num_outputs) {
return i;
}
template<typename traits, std::size_t i = 0, typename... tuple_t>
static inline typename std::enable_if<i < sizeof...(tuple_t), std::size_t>::type
for_each_in_tuple(const std::tuple<tuple_t...>& t, const TensorIterator &iter, const int num_outputs) {
if (i < (size_t)num_outputs) {
set_result<traits>(i, std::get<i>(t), iter, num_outputs);
return for_each_in_tuple<traits, i + 1, tuple_t...>(t, iter, num_outputs);
}
return i;
}
template<typename traits, typename... res_t>
static void set_results(const std::tuple<res_t...>& result, const TensorIterator &iter, const int num_outputs) {
AT_ASSERT(num_outputs >= 1);
std::size_t result_size = for_each_in_tuple<traits>(result, iter, num_outputs);
AT_ASSERT((size_t)num_outputs == result_size);
}
template <typename T, typename... Args>
struct all_same : guts::conjunction<
std::is_same<T, Args>...
> {};
// data_t is the input/output data type.
// acc_t is a type that contains all the necessary data
// to continue reducing.
// index_t is a one-dimensional index
//
// ops_t is such that &ops_t::reduce, &ops_t::combine, and &ops_t::project exist and satisfy
// the following.
// reduce: (acc_t, data_t, index_t) -> acc_t adds one data point to the accumulated value.
// combine: (acc_t, acc_t) -> acc_t combines two accumulated values into one.
// project: acc_t -> out_t finishes the reduction, getting the required output.
//
// Additionally, acc_t must be default-constructible:
// acc_t {} is an identity for combine,
// and project(acc_t {}) is the value of the operation on zero elements.
//
// The point of `combine` is to support parallelization -
// the idea is to one sequence of `reduce` calls per thread of execution,
// and then to combine them at the end with `combine`.
//
// If there is more than one output element,
// our parallelization strategy is to use one thread for each of them,
// which means that `combine` will never be called.
//
// If, on the other hand, there is only one, then we split the input into
// into several pieces, reduce each separately, and then combine them.
template <typename ops_t, typename init_t>
void binary_kernel_reduce(TensorIterator& iter, ops_t ops, init_t init) {
using rf_t = decltype(&ops_t::reduce);
using cf_t = decltype(&ops_t::combine);
using pf_t = decltype(&ops_t::project);
using r_traits = binary_function_traits<rf_t>;
using c_traits = binary_function_traits<cf_t>;
using p_traits = unary_function_traits<pf_t>;
using acc_t = typename p_traits::arg1_t;
using data_t = typename r_traits::arg2_t;
static_assert(
all_same<
acc_t,
init_t,
typename r_traits::arg1_t,
typename r_traits::result_type,
typename c_traits::arg1_t,
typename c_traits::arg2_t,
typename c_traits::result_type>::value,
"all accumulate types must match");
static_assert(
std::is_default_constructible<acc_t>::value,
"the accumulate type must be default-constructible"
);
const int num_outputs = iter.noutputs();
iter.foreach_reduced_elt([&ops, &init, num_outputs](TensorIterator &sub_iter) {
auto reduction_body = [&ops, &sub_iter, num_outputs](acc_t acc, int64_t begin, int64_t end) -> acc_t {
int ntensors = sub_iter.ntensors();
sub_iter.serial_for_each([&acc, &ops, num_outputs, ntensors, begin](char** data, const int64_t* strides, int64_t size) {
AT_ASSERT(ntensors - num_outputs == 1);
char *in = data[ntensors - 1];
int64_t stride = strides[ntensors - 1];
for (int64_t i = 0; i < size; ++i) {
acc = ops.reduce(acc, *(data_t*)in, begin + i);
in += stride;
}
}, {begin, end});
return ops.translate_idx(acc, sub_iter.view_offsets()[0]);
};
acc_t total_acc = init;
auto numel = sub_iter.numel();
if (numel < at::internal::GRAIN_SIZE || at::get_num_threads() == 1 ||
at::in_parallel_region()) {
total_acc = reduction_body(total_acc, 0, numel);
} else {
int max_threads = at::get_num_threads();
AT_ASSERT(max_threads > 0);
static_assert(
!std::is_same<acc_t, bool>::value,
"Concurrently modifying different references into std::vector<bool> is UB."
);
std::vector<acc_t> buffer((unsigned)max_threads, init);
at::parallel_for(0, numel, internal::GRAIN_SIZE,
[&](int64_t begin, int64_t end) {
auto& acc = buffer[at::get_thread_num()];
acc = reduction_body(acc, begin, end);
}
);
for (int i = 0; i < max_threads; ++i) {
total_acc = ops.combine(total_acc, buffer[i]);
}
}
set_results<r_traits>(ops.project(total_acc), sub_iter, num_outputs);
});
}
template <typename func_t, typename vec_func_t>
void binary_kernel_reduce_vec(TensorIterator& iter, func_t op, vec_func_t vop, double ident = 0) {
using traits = binary_function_traits<func_t>;
static_assert(
all_same<
typename traits::result_type,
typename traits::arg1_t,
typename traits::arg2_t>::value,
"all types must match");
iter.output().fill_(ident);
iter.parallel_reduce([&](char** data, const int64_t* strides, int64_t size0, int64_t size1) {
int64_t outer_strides[] = { strides[2], strides[3] };
if (is_contiguous_reduction<traits>(strides)) {
// input is contiguous in dim 0, output is reduced in dim 0
UNARY_OUTER_LOOP(data, outer_strides, size1, [&] {
vectorized_inner_reduction(data, size0, op, vop);
});
} else if (is_outer_reduction<traits>(strides)) {
// input and output are contiguous in dim 1
int64_t inner_stride = strides[1]; // stride of input in dim 0
vectorized_outer_reduction(data, inner_stride, size0, size1, op, vop);
} else {
UNARY_OUTER_LOOP(data, outer_strides, size1, [&] {
char* ptrs[3] = { data[0], data[0], data[1] };
int64_t inner_strides[3] = { strides[0], strides[0], strides[1] };
basic_loop(ptrs, inner_strides, 0, size0, op);
});
}
});
}
}}} // namespace at::native::<anonymous>