(Re-)introduce broadcast!(::typeof(identity), ...) for sparse arrays for performance

Author: martinholters

base/sparse/higherorderfns.jl

@@ -148,7 +148,13 @@ ambiguityfunnel{Tf}(f::Tf, x, y) = _aresameshape(x, y) ? _noshapecheck_map(f, x,
 broadcast(::typeof(+), x::SparseVector, y::SparseVector) = ambiguityfunnel(+, x, y) # base/sparse/sparsevectors.jl:1266
 broadcast(::typeof(-), x::SparseVector, y::SparseVector) = ambiguityfunnel(-, x, y) # base/sparse/sparsevectors.jl:1266
 broadcast(::typeof(*), x::SparseVector, y::SparseVector) = ambiguityfunnel(*, x, y) # base/sparse/sparsevectors.jl:1266
-
+# specializations to improve performance for C .= A
+function broadcast!(::typeof(identity), C::SparseVector, A::SparseVector)
+    _checksameshape(C, A); return copy!(C, A)
+end
+function broadcast!(::typeof(identity), C::SparseMatrixCSC, A::SparseMatrixCSC)
+    _checksameshape(C, A); return copy!(C, A)
+end
 
 # (4) _map_zeropres!/_map_notzeropres! specialized for a single sparse vector/matrix
 "Stores only the nonzero entries of `map(f, Array(A))` in `C`."