Certain unsafe operations were allowed to propagate across a
`lambda' boundary (where space safety is known not to be an issue),
which could lead to duplicate uses of a "once used" variable if
the relevant `lambda' is inlined.
Furthermore, `lambda' boundary crossing wasn't detected in the case
that the operation to propagate was propagated through an intermediate
variable without a `lambda' crossing.
Merge to 5.2.1
(cherry picked from commit 7850a26dfe)
b7b273895a