Split ZEND_SEND_VAR_NO_REF into ZEND_SEND_VAR_NO_REF and ZEND_SEND_VAR_NO_REF_EX (similar to ZEND_SEND_VAL) and remove ZEND_ARG_* flags.

Typo & cleanup

Replace BB end with BB len

And support empty blocks everywhere.

Fix phi placement for pi targets

If the pi target has multiple predecessors, we need to place a
phi there. However it's not possible to express this in terms of
dominance frontiers,

Fix phi placement for pi targets

If the pi target has multiple predecessors, we need to place a
phi there. However it's not possible to express this in terms of
dominance frontiers, so we need to explicitly add it to the phi
set.

This does not yet solve the problem of non-minimal SSA for the
case where the target has multiple predecessors, but dominates
all predecessors (apart from the one creating the pi) -- but
that's an existing issue.

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Explicitly construct phi set during def propagation

Previously the phi set was first computed during def propagation
and then computed again (per-block) during actual phi placement.

Explicitly construct phi set during def propagation

Previously the phi set was first computed during def propagation
and then computed again (per-block) during actual phi placement.
This commit changes this to store the phi set computed during
def propagation.

This makes SSA construction slightly faster (5%), but the main
purpose here is to pave the way for the next commit.

This also fixes a potential issue with the handling of irreducible
loops -- they generated additional phis, but these were not
accounted for in def propagation. (Though I'm not sure if we can
even have any irreducible loops right now.)

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Take pi defs into account when propagating defs

Previously pi placement happened after initial phi placement.
Afterwards a second phi placement pass was performed, however it
incorre

Take pi defs into account when propagating defs

Previously pi placement happened after initial phi placement.
Afterwards a second phi placement pass was performed, however it
incorrectly only placed phis on the dominance frontier, rather
than the iterated dominance frontier.

This is fixed by moving pi placement before the propagation of
defs on the iterated DFs, and adding a def for each added pi.

While this ensures that we generate correct conservative SSA, there
is still one remaining case in which we may generate non-minimal
SSA form. Consider:

|1|
|pi
v
|2|<--\
| |
\----/

The pi is semanically located along the edge 1->2, however we place
it (and its def point) in 2, thus leading to the generation of an
additional (trivial) phi in 2.

Conflicts:
ext/opcache/Optimizer/zend_ssa.c

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Make pi placement independent of phi placement

This interdependence is problematic because we can't propagate pi
def points in the initial dominance frontier propagation. The used
ru

Make pi placement independent of phi placement

This interdependence is problematic because we can't propagate pi
def points in the initial dominance frontier propagation. The used
rule for multiple-predecessor blocks may also miss cases where
placing the pi would have been useful.

The new heuristic for pi placement checks that a) the variable is
live-in and b) for the "from" block that generated the pi, the
other successor does not dominate all other predecessors of the
"to" block.

The purpose of case b) may be illustrated with an example:

if (is_int($i)) {
// place pi here
}
// but don't place pi here

The reason we do not want to place the second pi is that we generally
place pis in positive+negative pairs, and in this case the pair
would merge in a phi and cancel out, so we get no useful information
out of it.

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Drop some unnecessary checks

Introduce ZEND_BITSET_FOREACH macros

Adjust DFG allocation size

Now we need one set less...

Merge def and gen sets

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

Merge def and gen sets

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).

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Fix SSA for SEND_UNPACK

Fixed handling of return statement without a value.

Added missing "break"

Use return type hints for type inference and eliminate useless VERIFY_RETRUN_TYPE opcodes.

Fix build

Combine conditions

Cleanup OP_DATA usage. Now only first operand of OP_DATA is used for ASSIGN_DIM, ASSIGN_OBJ and ASSIGN_OP (DIM/OBJ) instructions.

Move pi placement into separate function

Non-functional change, just moving code. This makes it easier to
change the order of operations.

Respect RC_INFERENCE during DFG construction

To avoid inserting phis that are only relevant with rc inference
enabled. Suprisingly, this affects only 0.8% of phis.

Fix SSA for ZEND_YIELD

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.

Add support for Pi type constraints

Supports TYPE_CHECK and IS_IDENTICAL for now.

Introduced BIND_STATIC opcode instead of FETCH_R/FETCH_W(static)+ASSIGN/ASSIGN_REF (similar to BIND_GLOBAL).
In the future we may refer to static variable by index instead of name, to eliminate h

Introduced BIND_STATIC opcode instead of FETCH_R/FETCH_W(static)+ASSIGN/ASSIGN_REF (similar to BIND_GLOBAL).
In the future we may refer to static variable by index instead of name, to eliminate hash lookup.

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Make PI construction human-readable

Also makes it easy to add PIs for TI.

Happy new year (Update copyright to 2016)