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Revert "Avoid allocations in views of views (#53231)" #57044

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Jan 14, 2025
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Revert "Avoid allocations in views of views (#53231)" #57044

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6 changes: 3 additions & 3 deletions base/subarray.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -291,18 +291,18 @@ reindex(idxs::Tuple{Slice, Vararg{Any}}, subidxs::Tuple{Any, Vararg{Any}}) =

# Re-index into parent vectors with one subindex
reindex(idxs::Tuple{AbstractVector, Vararg{Any}}, subidxs::Tuple{Any, Vararg{Any}}) =
(@_propagate_inbounds_meta; (maybeview(idxs[1], subidxs[1]), reindex(tail(idxs), tail(subidxs))...))
(@_propagate_inbounds_meta; (idxs[1][subidxs[1]], reindex(tail(idxs), tail(subidxs))...))

# Parent matrices are re-indexed with two sub-indices
reindex(idxs::Tuple{AbstractMatrix, Vararg{Any}}, subidxs::Tuple{Any, Any, Vararg{Any}}) =
(@_propagate_inbounds_meta; (maybeview(idxs[1], subidxs[1], subidxs[2]), reindex(tail(idxs), tail(tail(subidxs)))...))
(@_propagate_inbounds_meta; (idxs[1][subidxs[1], subidxs[2]], reindex(tail(idxs), tail(tail(subidxs)))...))

# In general, we index N-dimensional parent arrays with N indices
@generated function reindex(idxs::Tuple{AbstractArray{T,N}, Vararg{Any}}, subidxs::Tuple{Vararg{Any}}) where {T,N}
if length(subidxs.parameters) >= N
subs = [:(subidxs[$d]) for d in 1:N]
tail = [:(subidxs[$d]) for d in N+1:length(subidxs.parameters)]
:(@_propagate_inbounds_meta; (maybeview(idxs[1], $(subs...)), reindex(tail(idxs), ($(tail...),))...))
:(@_propagate_inbounds_meta; (idxs[1][$(subs...)], reindex(tail(idxs), ($(tail...),))...))
else
:(throw(ArgumentError("cannot re-index SubArray with fewer indices than dimensions\nThis should not occur; please submit a bug report.")))
end
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25 changes: 0 additions & 25 deletions test/subarray.jl
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Expand Up @@ -1027,31 +1027,6 @@ catch err
err isa ErrorException && startswith(err.msg, "syntax:")
end


@testset "avoid allocating in reindex" begin
a = reshape(1:16, 4, 4)
inds = ([2,3], [3,4])
av = view(a, inds...)
av2 = view(av, 1, 1)
@test parentindices(av2) === (2,3)
av2 = view(av, 2:2, 2:2)
@test parentindices(av2) === (view(inds[1], 2:2), view(inds[2], 2:2))

inds = (reshape([eachindex(a);], size(a)),)
av = view(a, inds...)
av2 = view(av, 1, 1)
@test parentindices(av2) === (1,)
av2 = view(av, 2:2, 2:2)
@test parentindices(av2) === (view(inds[1], 2:2, 2:2),)

inds = (reshape([eachindex(a);], size(a)..., 1),)
av = view(a, inds...)
av2 = view(av, 1, 1, 1)
@test parentindices(av2) === (1,)
av2 = view(av, 2:2, 2:2, 1:1)
@test parentindices(av2) === (view(inds[1], 2:2, 2:2, 1:1),)
end

@testset "isassigned" begin
a = Vector{BigFloat}(undef, 5)
a[2] = 0
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