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Strongly hint but don't force the compiler to unroll a some loops in the tensor executor. This results in up to 27% faster code.

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This commit is contained in:
Benoit Steiner 2016-05-05 09:25:55 -07:00
parent 7875437ca0
commit a4d6e8fef0
1 changed files with 12 additions and 10 deletions
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22
unsupported/Eigen/CXX11/src/Tensor/TensorExecutor.h
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@ -59,13 +59,14 @@ class TensorExecutor<Expression, DefaultDevice, true>
{
const Index size = array_prod(evaluator.dimensions());
const int PacketSize = unpacket_traits<typename TensorEvaluator<Expression, DefaultDevice>::PacketReturnType>::size;
// Manually unroll this loop since compilers don't do it.
// Give the compiler a strong hint to unroll the loop. But don't insist
// on unrolling, because if the function is expensive the compiler should not
// unroll the loop at the expense of inlining.
const Index UnrolledSize = (size / (4 * PacketSize)) * 4 * PacketSize;
for (Index i = 0; i < UnrolledSize; i += 4*PacketSize) {
evaluator.evalPacket(i);
evaluator.evalPacket(i+PacketSize);
evaluator.evalPacket(i+2*PacketSize);
evaluator.evalPacket(i+3*PacketSize);
for (Index j = 0; j < 4; j++) {
evaluator.evalPacket(i + j * PacketSize);
}
}
const Index VectorizedSize = (size / PacketSize) * PacketSize;
for (Index i = UnrolledSize; i < VectorizedSize; i += PacketSize) {
@ -104,12 +105,13 @@ struct EvalRange<Evaluator, Index, true> {
if (last - first >= PacketSize) {
eigen_assert(first % PacketSize == 0);
Index last_chunk_offset = last - 4 * PacketSize;
// Manually unroll this loop since compilers don't do it.
// Give the compiler a strong hint to unroll the loop. But don't insist
// on unrolling, because if the function is expensive the compiler should not
// unroll the loop at the expense of inlining.
for (; i <= last_chunk_offset; i += 4*PacketSize) {
evaluator.evalPacket(i);
evaluator.evalPacket(i+PacketSize);
evaluator.evalPacket(i+2*PacketSize);
evaluator.evalPacket(i+3*PacketSize);
for (Index j = 0; j < 4; j++) {
evaluator.evalPacket(i + j * PacketSize);
}
}
last_chunk_offset = last - PacketSize;
for (; i <= last_chunk_offset; i += PacketSize) {