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re: the ISL stream is flat -- refute the "needs coroutine entry points" blocker

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Two files (isl_report.py's docstring and structures/isl-builtins.md) recorded the
same blocker on a faithful per-phase condition listing: that it needs the coroutine
entry points from start_coroutine's operand.  Measured against isl.call_sites(),
which enumerates by scanning the encoding rather than by decoding and so is an
independent denominator:

  linear + jumps, stopping at ret (what the tool did)   133 / 2846 =   4.7%
  linear + jumps, continuing past ret                  2275 / 2846 =  79.9%
  ... + following start_coroutine (the recorded fix)   2355 / 2846 =  82.7%
  plain linear decode, no control flow at all          2846 / 2846 = 100.0%

Following the coroutine entries buys 2.8 points.  Disc-wide, a plain linear decode
from the first phase base reaches 25705/25705 call sites over all 28 stages, and
28/28 decode clean to code_end with no desync.

The real bug was isl.dis ending on `if op == 20: break`.  Op 20 is `ret`, but this
is a coroutine VM -- the thread suspends and resumes at the FOLLOWING instruction,
so code continues past it.  dis() now takes stop_at_ret (default True, preserving
the old output: data/isl-stage02.txt regenerates byte-identical) and
isl.linear_offsets() is the correct walk.

By-product, kept with its control: start_coroutine's target is staged slot 0 --
73/83 phase-1 sites land on a valid instruction, against a 38.7% chance rate for an
arbitrary 4-aligned offset.

New artefact data/isl-stage02-phase-ends.txt with a committed generator
(isl_report.py phase-ends).  It shows END_PHASE's call site is the WRONG place to
read a clear condition: all 12 Stage-02 sites sit in one stereotyped outro.  Not
settled, and stated as such: op10/op13/op14/op21/op23 are unread handlers, so the
condition in the poll loop upstream cannot be named yet.
This commit is contained in:
Sylpheed RE agent
2026-08-27 05:00:49 +00:00
parent ef4e975a47
commit f41847701c
6 changed files with 567 additions and 11 deletions
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8
docs/re/structures/isl-builtins.md
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@@ -601,8 +601,12 @@ Counting call sites in `Stage02.ssb` (`data/isl-stage02.txt`, regenerated by
⚠️ The sibling artefact `data/isl-stage02-conditions.txt` **predates the name
corrections above** — it still prints `yield`, `await_label` and `push_trigger`,
and its operand rendering predates the staging fix. It has no committed
generator; reproducing it needs the coroutine entry points, which
`start_coroutine`'s operand carries and the tool does not yet follow.
generator. ~~reproducing it needs the coroutine entry points, which
`start_coroutine`'s operand carries and the tool does not yet follow.~~
🔴 **That reason is REFUTED** — see [isl-stream-is-flat](../isl-stream-is-flat.md).
The stream is flat; a plain linear decode reaches **25705/25705** call sites
across all 28 stages. What broke the naive decode was `isl.dis` stopping at
op 20 (`ret`), which in a coroutine VM is a *yield*, not an end of code.
| built-in | sites |
|---|---|