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optimize vectorized reductions by peeling the loop:

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- x2 for squaredNorm() on double
 - peeling the loop with a peeling factor of 4 leads to even better perf
   for large vectors (e.g., >64) but it makes more difficult to keep good performance on smaller ones.
This commit is contained in:
Gael Guennebaud 2011-11-12 09:19:48 +01:00
parent c110abb7d2
commit 3e4a68cc60
1 changed files with 19 additions and 6 deletions
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23
Eigen/src/Core/Redux.h
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@ -219,15 +219,28 @@ struct redux_impl<Func, Derived, LinearVectorizedTraversal, NoUnrolling>
alignment = bool(Derived::Flags & DirectAccessBit) || bool(Derived::Flags & AlignedBit) alignment = bool(Derived::Flags & DirectAccessBit) || bool(Derived::Flags & AlignedBit)
? Aligned : Unaligned ? Aligned : Unaligned
}; };
const Index alignedSize = ((size-alignedStart)/packetSize)*packetSize; const Index alignedSize2 = ((size-alignedStart)/(2*packetSize))*(2*packetSize);
const Index alignedSize = ((size-alignedStart)/(packetSize))*(packetSize);
const Index alignedEnd2 = alignedStart + alignedSize2;
const Index alignedEnd = alignedStart + alignedSize; const Index alignedEnd = alignedStart + alignedSize;
Scalar res; Scalar res;
if(alignedSize) if(alignedSize)
{ {
PacketScalar packet_res = mat.template packet<alignment>(alignedStart); PacketScalar packet_res0 = mat.template packet<alignment>(alignedStart);
for(Index index = alignedStart + packetSize; index < alignedEnd; index += packetSize) if(alignedSize>packetSize) // we have at least two packets to partly unroll the loop
packet_res = func.packetOp(packet_res, mat.template packet<alignment>(index)); {
res = func.predux(packet_res); PacketScalar packet_res1 = mat.template packet<alignment>(alignedStart+packetSize);
for(Index index = alignedStart + 2*packetSize; index < alignedEnd2; index += 2*packetSize)
{
packet_res0 = func.packetOp(packet_res0, mat.template packet<alignment>(index));
packet_res1 = func.packetOp(packet_res1, mat.template packet<alignment>(index+packetSize));
}
packet_res0 = func.packetOp(packet_res0,packet_res1);
if(alignedEnd>alignedEnd2)
packet_res0 = func.packetOp(packet_res0, mat.template packet<alignment>(alignedEnd2));
}
res = func.predux(packet_res0);
for(Index index = 0; index < alignedStart; ++index) for(Index index = 0; index < alignedStart; ++index)
res = func(res,mat.coeff(index)); res = func(res,mat.coeff(index));