It seems dag_set_live_vars still served a purpose after all, but I don't
feel like bringing it as I'd rather implement its param handing in
dagnode_set_edges. I've now got a test case for it, though the test
currently causes the VM to segfault (even with pr_boundscheck 2!).
If the final block ends in a conditional statement, appending return to the
block will hide the conditional statement from the flow analyzer. This may
cause the conditional statement's destination node be become unreachable
according to the analyzer and thus eliminated. The label for the branch
then loses its target sblock and thus the code generator will produce a
zero-distance jump resulting in an infinite loop.
Thus, if the final block ends in a conditional statement (or, for
completeness, a call statement), append a new empty block before adding the
return statement.
It turns out they're not getting allocated properly (they're put in the
function's locals defspace rather than near data), but fixing it proved a
little more problematic than expected, so the test is marked as XFAIL for
now to remind me to fix it.
