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

KristofferC · KristofferC · web-flow · commit b23f557e80ca · 2025-01-14T10:28:34.000-05:00
This reverts commit 2bd4cf8. (#53231) The reason for this revert is that it caused exponential blowup of types in iterated views causing some packages to simply freeze when doing something that worked ok in 1.10. In my opinion, the perf gain from the PR is not outweighed by the "risk" of hitting this compilation blowup case. Fixes #56760. Co-authored-by: KristofferC <kristoffer.carlsson@juliacomputing.com>
diff --git a/base/subarray.jl b/base/subarray.jl
@@ -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
diff --git a/test/subarray.jl b/test/subarray.jl
@@ -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
