[Bug target/85223] [nvptx] nvptx_single needs rewrite

[vries at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85223

--- Comment #1 from Tom de Vries <vries at gcc dot gnu.org> ---
> that minimized uses of head and tail,

Also, the use of the long-lived non-descriptive variable "before" needs to be
cleaned up.