Syplheed-Reborn/docs/re/isl-stream-entry-points.md

✅ The mission-level 0x1883 record: one entry point and one code/data boundary

Every phase exit in all 28 stages is now reachable. data/isl-phase-guards-all.txt went from 5 of 177 exits unreachable to 0.

The hunt, including the part that failed

The first step was the cheap one: take each unreached routine's entry offset and look for it as a word anywhere in the file. It is not there, in any encoding:

entry encoded as	appears as a word	control (reached offsets)
phase-relative	6.6 %	11.5 %
absolute	1.6 %	3.3 %
phase-relative / 4	1.6 %	6.6 %
absolute / 4	0.0 %	8.2 %

Every variant sits at or below the control, so nothing in the bytecode names these routines. That is a real negative, and it ruled out the whole family of "some instruction operand points at them".

It also ruled out dead code: the 3 069 unreached instructions in Stage 02 contain 485 calls, including start_coroutine ×75, squadron_attack ×59, set_group_speed ×42 and objective_marker ×13. That is live mission logic.

✅ The answer is in the mission-level stream

isl-bytecode.md records that the stream at +0x24 holds three 0x1883 records, one per phase, whose operand is the phase's code base, and notes they each end "in a pair of plausible ISL entry offsets". They are exactly that. The record is

0x1883, base_delta, size, 0, entry_a, entry_b      ; entries PHASE-RELATIVE

Measured over all 28 stages: 82 of 88 of those values land on a valid instruction — 93.2 %, against a 38.6 % chance rate. ⚠️ That test was too weak — see What entry_a really is below. A trailing data record has length 8 and so passes "nonzero, even length"; the 93.2 % counted data as code. The entry_b result stands on a different footing: those targets were matched against isl.call_sites(), an independent enumeration.

And for Stage 02 the second entry of each record is the phase's force-end handler:

base 0x0000E4 -> 0x014848, 0x01482C     <- 0x1482C was an unreachable exit
base 0x014AA8 -> 0x024A0C, 0x0249F0
base 0x024B4C -> 0x034AC8, 0x034A10     <- 0x34A10 was an unreachable exit

Both of Stage 02's unreachable exits are named here, and phase 2's 0x249F0 — already reachable — is the same slot, which is the consistency check.

Seeding these as CFG entries: exits unreachable 5 → 0 across the disc.

🔑 It also reads: those exits now show 0 necessary conditions, because they are entry points rather than code reached through tests. A handler the engine can enter directly, with no preconditions, is what FORCE_END_PHASE should look like.

⚠️ Seeded in one place, and the count did not move

The first attempt added the entries to conditions() and reported reach 85.0 % → 85.0 %, exits 5 → 5. Nothing moved, which is the signal. dominating_conditions() builds its own entry set and did not use the one I had patched — the same fix-the-instance-not-the-class mistake that cost 22× its own size earlier in this corpus. With both patched: exits 5 → 0.

🟡 Not settled

• Reach only went 85.0 % → 85.2 %. These records name a handful of routines, not the ~15 % of code still unreached. What starts the rest is still open — and the negative above says it is not an operand in the file.
• entry_a is unidentified. entry_b is the force-end handler in the three Stage-02 records; what the first entry of each pair is has not been checked.
• 6 of 88 values do not land on an instruction. Not investigated — they may be absent phases, a different record variant, or a decode edge.

🔴 What entry_a really is — NOT an entry point

Disassembling the three Stage-02 entry_a targets shows opcodes 0x19 and 0x1A, and the dispatcher's table has 25 entries (cmplwi 0x18). Those are not instructions at all:

014848: 00000819  tag 19  00000019        int 25
014850: 00000819  tag 19  00002B20        int
014858: 0000081A  tag 1A  00000000        float 0.0
014860: 00000819  tag 19  00000005        int 5
014868: 00000819  tag 19  00002B88        int
014870: 0000081A  tag 1A  3F000000        float 0.5

Each phase region ends with a trailing DATA table of 8-byte typed records — tag 0x19 = int, tag 0x1A = IEEE float — and entry_a is where it starts.

Confirmed across the disc: in 44 of 44 phases, the first offset whose opcode exceeds 0x18 is exactly that phase's entry_a. Zero exceptions. Only two tags ever appear: 1 394 × 0x19 and 675 × 0x1A.

So the record is 0x1883, base, size, 0, code_end, force_end_handler — one boundary and one entry.

🟡 The table's contents are not decoded. Its int values do land on the instruction stream more often than chance (46/51 vs 29.5 %), but 0 of them are unreached run-starts — so this is not what starts the unreachable code either.

✅ And the decoder was reading that data as code

isl.linear_offsets was decoding all 2 069 of those records as instructions, 1.23 % of the stream. Fixed by stopping each phase's walk at its boundary:

	before	after
decoded instructions	168 251	166 182 = 168 251 − 2 069
records with opcode > 0x18	2 069	0
call sites covered	25 705 / 25 705	25 705 / 25 705
exits unreachable	0	0
conditions with unknown LHS	400	400

⚠️ The first attempt at that fix destroyed 36 % of the stream — 168 251 → 107 596, exits 0 → 74 — because linear_offsets is one global walk from the first phase base, so stopping at phase 1's table lost every later phase. It has to skip the region and resume at the next base. A count moving hard in the wrong direction is the same signal as one that will not move.