The safe-for-space pass could add clearing operations on "typed"
stack positions, which are known to contain a fixnum, flonum, or
extflonum. Non-clearing references, however, were not annotated to
indicate that clearing references were present, since clearing is
not expected on typed positions.
Along the lines of not expecting clearing, the bytecode validator's
encoding of the stack doesn't accomodate both "has a type" and "claims
never to be cleared", so it couldn't detect the bytecode compiler
bug. (Also, this problem didn't show up in the HOSC paper's model of
the validator, because the model pre-dates type tracking.)
Fix the bytecode compiler's space-safety pass so that it never inserts
clearing operations for typed stack positions. Then, the validator can
simply reject any attempt to clear a typed position.
Also, annotate applications generated by lifting as safe-for-space
tail calls.
Merge to v5.3.4
7ad1ddab64