load-time-value

(load-time-value form [read-only-p])

Evaluates form once per occurrence in the source, not once per use: the result is computed the first time that occurrence is reached and reused from then on. read-only-p is accepted and ignored.

The compiled backends hoist the result into a generated global filled on first use; the interpreter memoizes the occurrence. Filling is lazy rather than at program start, so an occurrence never reached is never evaluated -- which matters because a value form spliced out of a library routinely needs globals that later top-level forms initialize.

A value form cheap enough not to be worth a slot -- an atom, a variable read, or a quote/function/find-package wrapper -- keeps the plain lowering and is simply re-evaluated. The --no-gc backend never hoists.