Introduce a function barrier in Broadcast.copyto_nonleaf! to improve …

…type stability

during type widening

base/broadcast.jl

@@ -963,6 +963,13 @@ end
 @noinline throwdm(axdest, axsrc) =
     throw(DimensionMismatch("destination axes $axdest are not compatible with source axes $axsrc"))
 
+function copyupto!(newdest, dest, iter)
+    # Function barrier that makes the copying to newdest type stable
+    for II in iter
+        newdest[II] = dest[II]
+    end
+end
+
 function copyto_nonleaf!(dest, bc::Broadcasted, iter, state, count)
     T = eltype(dest)
     while true
@@ -976,9 +983,7 @@ function copyto_nonleaf!(dest, bc::Broadcasted, iter, state, count)
             # This element type doesn't fit in dest. Allocate a new dest with wider eltype,
             # copy over old values, and continue
             newdest = Base.similar(dest, promote_typejoin(T, typeof(val)))
-            for II in Iterators.take(iter, count)
-                newdest[II] = dest[II]
-            end
+            copyupto!(newdest, dest, Iterators.take(iter, count))
             newdest[I] = val
             return copyto_nonleaf!(newdest, bc, iter, state, count+1)
         end