The pass aims at convert conditional return from if to br_if to reduce the control flow stack depths.

(func (param i32)
    (if (local.get 0) (then (return)))
)

is equivalent to

(func (param i32)
    (br_if 0 (local.get 0)) ;; jump to the end of the function
)

INFO

This optimization does not result in any performance improvement on the V8 backend.