Drew T
2.4 KiB
§102 — A PLUMBING verdict can MASK a DIFF; and K&R is not always a codegen change (Phase 29 SESSION-22, func_8016EC0C)
Applying §99 to func_8016EC0C produced three results worth separating:
1. §99 GENERALISES — it dissolved a 1,617-site narrowing axis. conform_decls flagged
SCALAR-NARROWING (s32 → u8) across the fleet. Converting the DEFINITION to K&R promotes u8 →
s32, so the computed canonical became void func_8016EC0C(s32, s32) — the narrowing warning
disappeared entirely, leaving only a RETURN change (s32 → void) whose §85 precondition (no
caller consumes the return) was already satisfied. A caller-hazardous conform became a byte-neutral
one because of how the definition was written.
2. BUT K&R IS NOT AUTOMATICALLY A CODEGEN CHANGE — measure it, do not assume. K&R promotes, so
the CALLEE narrows (§43's in-place sll/andi tell) where ANSI assumes the caller did. That can
change bytes. Here it did not: match_one on both forms returned identical results — closeness
8, 88 ins, same residual. So the K&R rewrite was free. The rule is not "K&R always matches" nor
"K&R always differs" — it is: convert, then compare both forms against the target. (For
func_80175AB8/func_80175DA8 the K&R form is what banked; here it is byte-equal to ANSI.)
3. THE REAL FINDING: its "PLUMBING" verdict was HIDING a DIFF. The T14 census recorded
PLUMBING: conflicting types for func_8016EC0C, which reads as "recoverable, not a compiler wall".
It is not recoverable: with the decl axis clean the true verdict is SCHEDULE-REORDER, closeness
8, bucket permuter. cc1 reports the declaration conflict and never reaches the byte comparison,
so the plumbing error fires FIRST and the codegen verdict is never produced.
The law: PLUMBING is a verdict about the DECLARATIONS, never about the BODY. A census's PLUMBING bucket is therefore an upper bound on recoverable work, not a count of it — some entries are DIFFs wearing a plumbing costume, and you only learn which by clearing the plumbing and re-gating. Size a PLUMBING pool as "worth diagnosing", never as "worth banking".
Consequence for the backlog: func_8016EC0C is genuine permuter fuel (close=8,
SCHEDULE-REORDER) — unlike func_80176734/func_8017C974/func_80177B5C/func_80140958, which
measured structural and which the grinder's admission rule correctly rejects (§60/§60a).