* Move derivative taker to a separate file

* Add fold markers

* fix docs

* Merge local_isrc and local_isrc_strength and tag as vec for coalescced access

* Use new name

* Add an explanation about the optimization

* Back to loopy main with renamed transform

Co-authored-by: Andreas Kloeckner <inform@tiker.net>

* Optimize M2L for GPU

* Move icoeff_tgt to top level iname

* Fix substitution

* use loopy branch

* remove unused imports

* go back to loopy main

* Reduce diff

* move all optimizations to m2l_translation

* Remove extraneous FIXME

Co-authored-by: Andreas Klöckner <inform@tiker.net>