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do not pick full-packet if it'd result in more operations

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See comment and
<https://gitlab.com/libeigen/eigen/merge_requests/46#note_270622952>.
This commit is contained in:
Francesco Mazzoli 2020-01-14 15:20:24 +01:00 committed by Gael Guennebaud
parent 44df2109c8
commit e9cc0cd353
1 changed files with 15 additions and 3 deletions
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18
Eigen/src/Core/util/XprHelper.h
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@ -194,8 +194,12 @@ template<typename T> struct unpacket_traits
};
};
// If we vectorize regardless of alignment, always pick the full-sized packet,
// if we have enough data to process.
// If we vectorize regardless of alignment, pick the full-sized packet if:
// * The size is large enough;
// * Picking it will result in less operations than picking the half size.
// Consider the case where the size is 12, the full packet is 8, and the
// half packet is 4. If we pick the full packet we'd have 1 + 4 operations,
// but only 3 operations if we pick the half-packet.
//
// Otherwise, pick the packet size we know is going to work with the alignment
// of the given data. See
@ -203,7 +207,15 @@ template<typename T> struct unpacket_traits
// information.
#if EIGEN_UNALIGNED_VECTORIZE
template<int Size, typename PacketType,
bool Stop = Size==Dynamic || Size >= unpacket_traits<PacketType>::size || is_same<PacketType,typename unpacket_traits<PacketType>::half>::value>
bool Stop =
Size==Dynamic ||
(Size >= unpacket_traits<PacketType>::size &&
// If the packet size is 1 we're always good -- it will always divide things perfectly.
// We have this check since otherwise 1/2 would be 0 in the division below.
(unpacket_traits<PacketType>::size == 1 ||
(Size/unpacket_traits<PacketType>::size + Size%unpacket_traits<PacketType>::size) <=
(Size/(unpacket_traits<PacketType>::size/2) + Size%(unpacket_traits<PacketType>::size/2)))) ||
is_same<PacketType,typename unpacket_traits<PacketType>::half>::value>
#else
template<int Size, typename PacketType,
bool Stop = Size==Dynamic || (Size%unpacket_traits<PacketType>::size)==0 || is_same<PacketType,typename unpacket_traits<PacketType>::half>::value>