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[NFC][SYCL][Reduction] Use C++17 fold expressions #7208

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Oct 28, 2022
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[NFC][SYCL][Reduction] Use C++17 fold expressions #7208

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40 changes: 18 additions & 22 deletions sycl/include/sycl/reduction.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1653,15 +1653,13 @@ void initReduLocalAccs(bool Pow2WG, size_t LID, size_t WGSize,
const std::tuple<ReducerT...> &Reducers,
ReduTupleT<ResultT...> Identities,
std::index_sequence<Is...>) {
std::tie(std::get<Is>(LocalAccs)[LID]...) =
std::make_tuple(std::get<Is>(Reducers).MValue...);
((std::get<Is>(LocalAccs)[LID] = std::get<Is>(Reducers).MValue), ...);

// For work-groups, which size is not power of two, local accessors have
// an additional element with index WGSize that is used by the tree-reduction
// algorithm. Initialize those additional elements with identity values here.
if (!Pow2WG)
std::tie(std::get<Is>(LocalAccs)[WGSize]...) =
std::make_tuple(std::get<Is>(Identities)...);
((std::get<Is>(LocalAccs)[WGSize] = std::get<Is>(Identities)), ...);
}

template <typename... LocalAccT, typename... InputAccT, typename... ResultT,
Expand All @@ -1679,28 +1677,26 @@ void initReduLocalAccs(bool UniformPow2WG, size_t LID, size_t GID,
// give any impact into the final partial sums during the tree-reduction
// algorithm work.
if (UniformPow2WG || GID < NWorkItems)
std::tie(std::get<Is>(LocalAccs)[LID]...) =
std::make_tuple(std::get<Is>(InputAccs)[GID]...);
((std::get<Is>(LocalAccs)[LID] = std::get<Is>(InputAccs)[GID]), ...);
else
std::tie(std::get<Is>(LocalAccs)[LID]...) =
std::make_tuple(std::get<Is>(Identities)...);
((std::get<Is>(LocalAccs)[LID] = std::get<Is>(Identities)), ...);

// For work-groups, which size is not power of two, local accessors have
// an additional element with index WGSize that is used by the tree-reduction
// algorithm. Initialize those additional elements with identity values here.
if (!UniformPow2WG)
std::tie(std::get<Is>(LocalAccs)[WGSize]...) =
std::make_tuple(std::get<Is>(Identities)...);
((std::get<Is>(LocalAccs)[WGSize] = std::get<Is>(Identities)), ...);
}

template <typename... LocalAccT, typename... BOPsT, size_t... Is>
void reduceReduLocalAccs(size_t IndexA, size_t IndexB,
ReduTupleT<LocalAccT...> LocalAccs,
ReduTupleT<BOPsT...> BOPs,
std::index_sequence<Is...>) {
std::tie(std::get<Is>(LocalAccs)[IndexA]...) =
std::make_tuple((std::get<Is>(BOPs)(std::get<Is>(LocalAccs)[IndexA],
std::get<Is>(LocalAccs)[IndexB]))...);
auto ProcessOne = [=](auto &LocalAcc, auto &BOp) {
LocalAcc[IndexA] = BOp(LocalAcc[IndexA], LocalAcc[IndexB]);
};
(ProcessOne(std::get<Is>(LocalAccs), std::get<Is>(BOPs)), ...);
}

template <typename... Reductions, typename... OutAccT, typename... LocalAccT,
Expand All @@ -1713,23 +1709,23 @@ void writeReduSumsToOutAccs(
std::index_sequence<Is...>) {
// Add the initial value of user's variable to the final result.
if (IsOneWG)
std::tie(std::get<Is>(LocalAccs)[0]...) = std::make_tuple(std::get<Is>(
BOPs)(std::get<Is>(LocalAccs)[0], IsInitializeToIdentity[Is]
? std::get<Is>(IdentityVals)
: std::get<Is>(OutAccs)[0])...);
((std::get<Is>(LocalAccs)[0] = std::get<Is>(BOPs)(
std::get<Is>(LocalAccs)[0], IsInitializeToIdentity[Is]
? std::get<Is>(IdentityVals)
: std::get<Is>(OutAccs)[0])),
...);

if (Pow2WG) {
// The partial sums for the work-group are stored in 0-th elements of local
// accessors. Simply write those sums to output accessors.
std::tie(std::get<Is>(OutAccs)[OutAccIndex]...) =
std::make_tuple(std::get<Is>(LocalAccs)[0]...);
((std::get<Is>(OutAccs)[OutAccIndex] = std::get<Is>(LocalAccs)[0]), ...);
} else {
// Each of local accessors keeps two partial sums: in 0-th and WGsize-th
// elements. Combine them into final partial sums and write to output
// accessors.
std::tie(std::get<Is>(OutAccs)[OutAccIndex]...) =
std::make_tuple(std::get<Is>(BOPs)(std::get<Is>(LocalAccs)[0],
std::get<Is>(LocalAccs)[WGSize])...);
((std::get<Is>(OutAccs)[OutAccIndex] = std::get<Is>(BOPs)(
std::get<Is>(LocalAccs)[0], std::get<Is>(LocalAccs)[WGSize])),
...);
}
}

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