BFM-decomp/cookbook/C0047.md

§44 — The Phase-25 cheap-Opus giant batch: 5 structural levers + the §43 extension (2026-07-11, 6 crackers over the frontier giants)

A 6-agent cheap-Opus batch (each applying §43 + §31 + the giant recipe, escalate-if-new-class) over the 6 frontier giants (209–399 ins, all reach-134): 3 banked ×134 (func_80166994 §43; func_80135480; func_80163EC8), 4 pin-free/light-pin Fable5 seeds (the intrinsic wall), and 5 reusable levers. Meta- lesson: cheap-Opus-first was right — 3 giants + 5 levers + clean seeds for far less than 6× Fable5 — and §43 does NOT universally transfer: only 1 of 6 was a K&R-s16 case; each giant is its own class.

Lever 1 — §43 EXTENSION (widen the triage). The §43 tell "in-place sll aN,aN,16 on an arg reg" is too narrow. If the target holds arg0 in two callee regs (a non-coalesced duplicate, e.g. move s6,a0; move s7,s6 — one for a sign-test, one for a mask-test), the K&R s16 arg0; def reproduces that duplication with zero pins even when the sign-extend lands on the callee stash (sll $sN,16), not on $aN. (s16)cast collapses it to one reg. Rule: try the K&R s16 form whenever the target shows a duplicate-arg0 pattern, not only the in-place-$aN tell. (func_80133CD4.)

Lever 2 — pointer-var decl (avoid the &sym CSE-hoist). A held global pointer the target reloads per use: declare it extern u16 *D_xxx and access it directly (D_xxx[i]), NOT via (*(u16 **)&D_xxx)[i]. The &D_xxx form CSE-hoists the address into a callee reg (one lui;addiu, reused); the direct pointer-var form emits a fresh lui %hi; lw %lo per use — matching the target's reload pattern. (func_80133CD4, func_80135480.)

Lever 3 — block-scoped-pointer-split (local-alloc a reused output pointer). A single pointer reused to write multiple output-store groups across separate return tails becomes a global allocno pinned to one register, so it can't match a target that uses a different reg per tail. Split each store-group into its OWN block-scoped set-once / used-N / dies-once pointer → each becomes a local-alloc pseudo that picks the per-window lowest-free scratch, reproducing the target's per-tail allocation AND un-sticking coupled delay-slot fills elsewhere in the schedule. Pin-free. (func_80135480, 258 ins; §31 RC-4 extension.)

Lever 4 — cross-jump the duplicated tail (steer a "permuter-only" dbr class). For a shared reset/exit tail whose target shows call-arg-hoist into a branch delay slot + per-predecessor const-rematerialization: write the tail duplicated inline in BOTH predecessors, NOT as one shared goto block. gcc-2.7.2 jump.c cross-jumps the two copies, reproducing the exact dbr schedule (the call arg hoisted into the bnez delay slot serving both paths; the mask re-materialized per-predecessor in the j/beq delay slots, sharing a reg with the neighbouring lh). This cracks a residual §31 files under D1/D2 as permuter-only — it is steerable. (func_80163EC8, 234 ins; one benign $v0 pin.)

Lever 5 — the "intrinsic wall" (what cheap-Opus canNOT do → Fable5/permuter). The §37 allocno-tie / RC-6 pressure-lock / scheduling-position class: a pin-free structural seed floats at close 30–67 but the residual is a whole-function register permutation or a schedule-position tie-break that no C-lever reaches at the Opus tier — a caller-vs-callee allocno heuristic choice (func_80133CD4 s0v→$v0-vs-$s0). The cheap tier's job here is to produce a pin-free, structurally-complete seed (correct body + count, zero file-scope footprint) and hand off honestly (no forced/pinned false match). Escalation: Fable5 with tools/reference/gcc-2.7.2/ and the §34 gdb-on-cc1 find_reg/post_mark_life method (it reads the allocator's actual decision), or the pin-free seed → decomp-permuter.

⚠️ Phase-27 reclassification (regalloc-map §H, .run/giants/*.fable.md): the three functions this lever once cited as intrinsic — func_8014D820 "RC-6 pressure-lock", func_8016CBC0 "coalescing knife-edge", func_801670E4 "i=0/p co-location" — were each oracle-refuted: func_8016CBC0's callee-saved swap CRACKED byte-zero (a floor_log2 density gap, and gcc-2.7.2 has no coalescing so "knife-edge" was never the class), func_8014D820's block-0 cracked pin-free 261→110 (reused-load-temp serialization; the sched.c:3199 pin was a red herring), and func_801670E4's dominant residual is RC-6 register allocation, not S3 scheduling (proven by the reg_renumber-swap oracle). The pattern (continuing map §F/§G): an "RC-6 intrinsic" verdict is usually map-incompleteness — audit for a density/lifetime/merge lever before declaring it. And the old "NEVER ship the pinned variant — it SIGABRTs sibling TUs (§42e)" is corrected (§42e-CORRECTION): the SIGABRT was a staging macro-drop, now fixed; a pin whose live range does not cross a call is safe to propagate. Prefer pin-free still (fewer failure modes), but the pinned-×1 ceiling is not real.