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Help the compiler vectorize ranges::iota #4647

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merged 4 commits into from
May 20, 2024
Merged

Help the compiler vectorize ranges::iota #4647

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e8b62e8
Help the compiler vectorize `ranges::iota`
AlexGuteniev May 2, 2024
cedc297
missing `const`
AlexGuteniev May 2, 2024
c87c403
Aha!
AlexGuteniev May 2, 2024
8d4e563
Benchmark both algorithms.
StephanTLavavej May 16, 2024
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2 changes: 1 addition & 1 deletion benchmarks/src/iota.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -14,7 +14,7 @@ void bm(benchmark::State& state) {
std::vector<T> a(size);

for (auto _ : state) {
std::iota(a.begin(), a.end(), T{22});
std::ranges::iota(a, T{22});
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benchmark::DoNotOptimize(a);
}
}
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18 changes: 18 additions & 0 deletions stl/inc/numeric
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Expand Up @@ -567,6 +567,24 @@ namespace ranges {
_STL_INTERNAL_STATIC_ASSERT(weakly_incrementable<_Ty>);
_STL_INTERNAL_STATIC_ASSERT(indirectly_writable<_It, const _Ty&>);

if constexpr (_Iterator_is_contiguous<_It> && sized_sentinel_for<_Se, _It> && is_integral_v<_Ty>
&& sizeof(_Ty) >= 4) {
// TRANSITION, DevCom-10593477: help the compiler vectorize
const auto _Ptr = _To_address(_First);
const auto _Size = static_cast<size_t>(_Last - _First);

if (_STD _In_range<_Ty>(_Size)) {
const auto _Size_typed = static_cast<_Ty>(_Size);
for (_Ty _Ix = 0; _Ix != _Size_typed; ++_Ix) {
const _Ty _Const_val = _Val + _Ix;
_Ptr[_Ix] = _Const_val;
}

_Val += _Size_typed;
return _First + _Size;
}
}

const _Ty& _Const_val = _Val;
for (; _First != _Last; ++_First, (void) ++_Val) {
*_First = _Const_val;
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