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

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 <[email protected]>
(cherry picked from commit b23f557)

Author: KristofferC

base/subarray.jl

@@ -295,18 +295,18 @@ 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

test/subarray.jl

@@ -1026,31 +1026,6 @@ 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