make ReshapedArray carry size rather than strides

with this we can reuse mi

Author: N5N3

base/multidimensional.jl

@@ -628,8 +628,8 @@ module IteratorsMD
         fr, vr = _splitlinear(rs, last(iter.indices[1]))
         outer = @inbounds if ndims(oiter) == 1
             CartesianIndices((oiter.indices[1][vl:vr],))
-        else
-            view(ReshapedArray(oiter, (length(oiter),), ()), vl:vr)
+        else # reuse mi when possible
+            view(ReshapedArray(oiter, (length(oiter),), Base.safetail(rs.mi)), vl:vr)
         end
         # Use Generator to make inner loop branchless
         @inline function genouter(i::Int, I::CartesianIndex)

base/reshapedarray.jl

@@ -188,10 +188,10 @@ _reshape(R::ReshapedArray, dims::Dims) = _reshape(R.parent, dims)
 
 function __reshape(p::Tuple{AbstractArray,IndexStyle}, dims::Dims)
     parent = p[1]
-    strds = front(size_to_strides(map(length, axes(parent))..., 1))
-    strds1 = map(s->max(1,Int(s)), strds)  # for resizing empty arrays
-    mi = map(SignedMultiplicativeInverse, strds1)
-    ReshapedArray(parent, dims, reverse(mi))
+    szs = front(size(parent))
+    szs1 = map(s->max(1,Int(s)), szs)  # for resizing empty arrays
+    mi = map(SignedMultiplicativeInverse, szs1)
+    ReshapedArray(parent, dims, mi)
 end
 
 function __reshape(p::Tuple{AbstractArray{<:Any,0},IndexCartesian}, dims::Dims)
@@ -216,11 +216,11 @@ unaliascopy(A::ReshapedArray) = typeof(A)(unaliascopy(A.parent), A.dims, A.mi)
 dataids(A::ReshapedArray) = dataids(A.parent)
 
 @inline ind2sub_rs(ax, ::Tuple{}, i::Int) = (i,)
-@inline ind2sub_rs(ax, strds, i) = _ind2sub_rs(ax, strds, i - 1)
-@inline _ind2sub_rs(ax, ::Tuple{}, ind) = (ind + first(ax[end]),)
-@inline function _ind2sub_rs(ax, strds, ind)
-    d, r = divrem(ind, strds[1])
-    (_ind2sub_rs(front(ax), tail(strds), r)..., d + first(ax[end]))
+@inline ind2sub_rs(ax, szs, i) = _ind2sub_rs(ax, szs, i - 1)
+@inline _ind2sub_rs(ax, ::Tuple{}, ind) = (ind + first(ax[1]),)
+@inline function _ind2sub_rs(ax, szs, ind)
+    d, r = divrem(ind, szs[1])
+    (r + first(ax[1]), _ind2sub_rs(tail(ax), tail(szs), d)...)
 end
 offset_if_vec(i::Integer, axs::Tuple{<:AbstractUnitRange}) = i + first(axs[1]) - 1
 offset_if_vec(i::Integer, axs::Tuple) = i