Detangle linear indexing from non-scalar indexing #13614
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This result holds for both 3.3 and 3.7. Failures were all unrelated. |
This removes the LinearFast special cases from non-scalar indexing. Previously, we were manually hoisting the div/rem sub2ind calculation along the indexed strides, but LLVM seems to be just as capable at performing this optimization in the cases I have tested. Even better, though, this creates a clean separation between the array indexing fallbacks: * Scalar fallbacks use `ind2sub` and `sub2ind` to compute the required number of indices that the custom type must implement. * Non-scalar fallbacks simply "unwrap" the elements from AbstractArrays and use scalar indexing with the indices that were provided. * (CartesianIndices are also expanded to individual integers, but that is a smaller detail.) In all cases that I've tried, I've been unable to measure a performance difference. Indeed, the LLVM IR looks identical in my spot-checks, too.
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Detangle linear indexing from non-scalar indexing
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Given But your comment in the code & above seems to imply that LLVM is figuring out the |
mbauman
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Jan 11, 2016
Back in JuliaLang#13614 I changed the signature of _unsafe_getindex!, but I failed to update the BitArray methods... so they were just using the generic definitions. This is a very simple fix to restore the indexing performance for BitArrays.
This was referenced Jan 11, 2016
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This removes the LinearFast special cases from non-scalar indexing. Previously, we were manually hoisting the div/rem sub2ind calculation along the indexed strides, but LLVM seems to be just as capable at performing this optimization in the cases I have tested. Even better, though, this creates a clean separation between the array indexing fallbacks:
ind2subandsub2indto compute the required number of indices that the custom type must implement (as determined byBase.linearindexing).In all cases that I've tried, I've been unable to measure a performance difference. Indeed, the LLVM IR looks identical in my spot-checks, too.