the rewriter is capable of flattening the function
by returning early, and inverting simple conditions. More
complex conditions are just wrapped in "!(x)"

Change-Id: I028fd7b018dc7347c1b323b2a73ab99c18508faa
Reviewed-on: https://gerrit.libreoffice.org/45071Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
Tested-by: Noel Grandin <noel.grandin@collabora.co.uk>