The previous rules refected PHP-5 behavior and were completely wrong for PHP-7. (e.g. scalars don't have reference counters at all).
This change shouldn't affect anything, because results of this inference are not used yet.
For live-variable analysis it does not matter if def includes
variables that are previously use in the same block, the data flow
equations still have the same result. As such there is no need to
compute separate gen & def sets.
I'm keeping the name "def", because use of "gen" in this context is
pretty confusing (gen is usually the use set, not the def set).
Yield-by-ref defs a ref var, yield-by-var only defs an rc1/rcn var
if rc inference is used.
Also move BIND_LEXICAL where it belongs in DFG construction.
This opcodes inserts a local CV into the closure static variable
table. This replaces the previous mechanism of having static
variables marked as LEXICAL, which perform a symtable lookup
during copying.
This means a) functions which contain closures no longer have to
rebuild their symtable (better performance) and b) we can now track
used variables in SSA.
