Dominance said a phase cannot end unless X. A port also needs "once X holds, it
must end", and that is a must-reach set: nodes from which END_PHASE is unavoidable,
as a least fixpoint where n qualifies when it has successors and ALL of them qualify.
The conservatism is deliberate and is the honest answer: a loop never enters the set,
because a poll loop reaches its exit only if the polled predicate eventually becomes
true, which is a liveness property rather than a graph one.
A dominating condition is a TRIGGER when the successor it takes on being satisfied
lies in that set. Over all 28 stages: 732 dominating conditions, 234 triggers
(31.97%). isl_report.py phase-guards now tags every line precond / TRIGGER.
The split lands where it should. Stage 02's phase-1 objective exit is six
preconditions -- player alive, TCN004 destroyed, t <= 210, ADT102/ADT107/ADT113
destroyed -- and exactly ONE trigger: hp_pct_test(ADN101, 0) != 1. Destroying ADN101
is what fires the phase. That is a sentence a port can implement.
Per-exit distribution over 172 reachable exits: 89 have exactly one trigger, 42 have
none, 41 have several. The 42 with none are not a failure -- they are the exits no
branch fires; Stage 02's 0x006260 ends on read_freg(0) < 1200, a timeout, and time
passing is not a property of the graph, so declining to call it a trigger is correct.
Recorded as a heuristic rather than a rule: "the first trigger is the point of no
return" holds for 33 of the 41 multi-trigger exits, with 8 counterexamples where a
precondition appears after a trigger. The likely cause is that the listing is
ordered by file offset, which is not execution order -- coroutines and jumps let a
lower offset run later. Not asserted.
calls, phase-ends and conditions all regenerate byte-identical; the two phase-guards
artefacts change only by gaining the tags.
isl_report.py now accepts a directory, so the dominance analysis runs over the whole
disc: data/isl-phase-guards-all.txt, 177 phase exits, of which only 5 (2.8%) are
reachable from no static entry. CFG reach ranges 69.5% (S26) to 95.8% (S25), median
about 4 dominating conditions per exit.
The lopsided number in the per-stage table was the six TUTORIAL stages, S18-S23, each
with exactly ONE exit and exactly ONE dominating condition. That could have been a
degenerate result, so I looked: it is the same condition in all six,
END_PHASE <- builtin104() != 1
and isl-builtins.md reached built-in 104 from call-site USAGE alone -- "S18-S23 only,
followed by wait_s 39/39, preceded by end_coroutine 37/39, a textbook poll loop".
Usage said 104 is the tutorial's polled test; dominance says it is the tutorial's
clear condition. Two unrelated methods, six for six.
Stage 16 -- the corpus outlier whose script may be compiled C++ -- resolves as well:
read_freg(0) < 600, player_gauge0_test, player_gauge1_test, and two builtin141 calls
differing in a single argument (0 vs -4000), which is the shape of a position or zone
test. builtin141 is unread, so it is not named.
Stage 02's separate artefact regenerates byte-identical.
Also added: an RLIMIT_AS cap in isl_report's entry point. The dominator pass
OOM-killed a run earlier on this 15 GB box; a bad input should now fail the process
rather than the machine.
Still not settled and stated in the doc: dominance gives necessary, not sufficient,
conditions; the 5 unreachable exits need the trigger queue at phase+272; builtin104,
builtin141 and builtin7 all appear in clear conditions and are unread.
Closes the backlog's "which condition guards each END_PHASE". With the CFG from the
previous commit this is a graph query, not new machinery.
The obvious query is WRONG for this language, and I implemented it first: "one
successor reaches END_PHASE and the other does not" finds 1/62/1 guards across Stage
02's three phases, and the 1s are both the same read_freg(0) < 1200 timeout -- every
objective test missed. The cause is the dominant idiom: a POLL LOOP's loop-back
branch also reaches the exit, one iteration later, so neither successor discriminates.
The asymmetric 1/62/1 is what exposed it; a uniform number would have read as
plausible.
Dominance has no such blind spot: a condition dominates an exit when every path from
an entry passes through it, so it is NECESSARY for the phase to end that way, and a
poll loop's test dominates its own exit by construction. Iterative dominators
converge in 3 passes over 15670/18739 instructions (83.6%).
Result for Stage 02 -- every exit in all three phases is dominated by
unit_hp_pct(TCN001, Character_Player_Test) != 0, the player's ship being alive, which
falls out rather than being assumed. Beyond that, phase 1's objective exit requires
hp_pct_test on ADT102, ADT107 and ADT113; phase 3's requires ADT301 and ADT302;
read_freg(0) gates at 210 / 300 and times out at 1200; random(3) and random(5)
dominate only the exits that pick one of several closing lines.
Two of the 15 exits are reachable from NO static entry, both FORCE_END_PHASE. That
agrees with the independently measured 389 unreachable routines: they are started from
the trigger queue at phase+272, by data rather than code.
Practical note recorded: the first dominator run was OOM-killed -- 6743 nodes each
holding a Python set of up to 6743 elements. Integer bitmasks run in seconds.
Not settled, and said so: dominance gives necessary, not sufficient, conditions; only
Stage 02's artefact is committed; one listed condition is still an unresolved
<unknown>; read_freg's units are inferred from the gate values, not read.
calls, phase-ends and conditions all regenerate byte-identical.
