The linear walk's 10% unknown was a floor imposed by the method: a block entered only
by a branch has a well-defined state, just not one a straight-line pass can see.
tools/re-capture/isl_cfg.py replaces it with a worklist fixpoint that joins each
block's state over its ACTUAL predecessors -- a value survives only if every
predecessor agrees.
Over all 28 stages:
instructions reached by the CFG 85.0%
condition sites, unknown LHS 756 (10.00%) -> 402 (5.32%)
of those, never reached at all 389
joined away (predecessors disagree) 13
both resolve but DISAGREE 161 <- linear walk was wrong here
Those 161 are on top of the 889 the previous jmp fix caught.
Two zero-results on the way, both my own bug, both caught because the number looked
wrong rather than because a test failed:
* The first CFG run reached only 36% of instructions and made things WORSE (35%
unknown). Cause: the phase bases reach almost nothing. Most routines are
COROUTINES the engine starts from its trigger queue, with no static predecessor,
so every start_coroutine target has to be seeded as an entry.
* That seeding then found ZERO entries in a file with 216 start_coroutine calls,
because the target is staged in TWO steps -- special[0] = imm, then
local[0] = special[0] -- and I matched only the direct-immediate form.
Reachability went 36% -> 64% -> 85% as each was fixed.
The 389 still unreached are an honest limit rather than a gap: nothing in the bytecode
starts them; they are entered from the trigger queue at phase+272, by data rather than
code, so no purely static analysis reaches them.
isl_report.py conditions now uses isl_cfg; calls and phase-ends regenerate
byte-identical. Stage 02 unknowns drop from 71 to 25.
Reading builtin80's body (0x82268460) to name it: it is NOT a predicate. It
allocates a 20-byte object, stamps vtable 0x820A8CB0, magic 0xAB0311BA and the
unit's live object into it, pushes it onto a queue via the same helper push.i uses,
and returns 1 -- or 0 when the unit is absent. A command.
That made the conditions listing impossible: it showed a six-way switch
`if builtin80(TCT206) == 0 … == 5` on a function returning 1 or 0. Disassembling the
site shows two unconditional `jmp`s between the call and the compare, so 0x1B6C0 is
reached ONLY by a branch and its special[0] has nothing to do with builtin80.
op12 is unconditional -- the next instruction is never reached by fall-through -- and
the tracker walked through it exactly as it had walked through end_coroutine. Last
iteration I fixed the instance and not the class, leaving 22x more bad sites in place
than the fix removed.
A/B over all 28 stages, 7563 sites, resetting at jmp as well:
sites whose operands change 889 (11.75%)
LHS unresolved, before -> after 34 (0.45%) -> 756 (10.00%)
So the previous commit's headline "0.0% unresolved" was a MISSING CHECK, not a strong
result: the linear walk always had some value to report, and reporting it was the bug.
10% is the honest figure and the other 90% is trustworthy for a reason.
Also corrected: isl-unit-args.md illustrated its diff with 0x1B6C0, which is one of
the bogus sites. The UNIT_ARG result itself stands -- it came from reading
implementations, not from this listing -- but the example was picked from bad output.
Not done, and said so: recovering the 756 needs a dataflow join over each block's
actual predecessors, a CFG fixpoint rather than a linear pass. The branch targets are
all known so the CFG is available; the analysis is not written.
calls and phase-ends regenerate byte-identical; conditions changes on 187 lines.
The listing showed end_coroutine as the left-hand side of 34 comparisons disc-wide.
That is impossible -- it returns no value a script can test -- so it was the bug
reporting itself.
The recorded fix ("set special[0] only for built-ins that write [phase+164]") is
REFUTED. end_coroutine's handler 0x82272624 is `addi r11,r0,1 ; addi r3,r0,3 ;
stw r11,164(r31)` -- it DOES write [phase+164], so that filter would have kept it.
Reading the handler before writing the filter is what caught this.
The real cause: end_coroutine returns 3, which DESTROYS the thread. Execution does
not continue past it, so the instructions following it in the flat stream belong to
a different routine and every tracked value is stale. The linear walk that makes
the decode possible is exactly what walks across that boundary.
A/B over all 28 stages, 7563 sites, resetting the tracker at end_coroutine:
sites whose operands change 34 (0.45%)
LHS = end_coroutine, before -> after 34 -> 0
left as an explicit unknown 34 (0.45%)
The two counts being equal is the result: the leak was confined to exactly the sites
that displayed the impossible value, so the other 7529 conditions were never
affected. Those 34 now print "<unknown: reached after a coroutine boundary>".
Not done, and said so: their RHS is still exact and the LHS is recoverable by seeding
the tracker at coroutine entries, whose targets are staged slot 0 of start_coroutine.
data/isl-stage02-conditions.txt regenerated; calls and phase-ends both byte-identical.
The deque ops are an EXPRESSION STACK: push the left operand, evaluate the right
(a built-in call, whose result lands in special[0]), pop the comparand back into
special[1], compare. Tracking that through the linear decode is enough to recover
what each site tests.
Evidence the model is right, not just plausible:
push vs pop across all 28 stages 1877 vs 1877
files that underflow or end unbalanced 0 of 28
Stage 02 pop.i sites followed by cmp.i 319 / 319
ops immediately before a pop.i call x313, cmp.a x6
isl.conditions() recovers 7563 condition sites disc-wide with 0.0% left as an
unresolved special[N]; 83.2% have a built-in call as the LHS and 99.7% compare
against a plain number. Most-tested: hp_pct_test 1955, unit_state 1257,
unit_relation 796, dist_lt 450, unit_alive 413.
They read as conditions now:
if unit_alive(TCN105) != 1
if hp_pct_test(ADT308, 0) != 1
if dist_lt(ADT308, TCN000, 15000) != 1 (world unit = 1 m, so 15 km)
if unit_state(ADT308) == 1
data/isl-stage02-conditions.txt was a stale artefact with NO generator -- the thing
isl_report.py's docstring complained about. It has one now (isl_report.py
conditions). The calls and phase-ends artefacts both regenerate byte-identical, so
the change is additive.
Recorded rather than glossed: 15 of Stage 02's 965 sites (1.6%) attribute the LHS to
end_coroutine, which returns no value -- the tracker sets special[0] on EVERY call,
so those show a stale value and are wrong, not imprecise. The fix is to set it only
for built-ins that write [phase+164], which the vtable work makes checkable.
