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Drew T
34417179df
- PROBE ANSWERED (the SESSION-17 open item): a0's first use is body-line 41, a1's is 28
-> use order ALREADY matched the target's birth order while birth order was inverted.
The §31 RC-1/RC-2/RC-3 first-use-order hypothesis is REFUTED for this class; decl order
is inert too. Both retired, do not re-buy.
- ROOT CAUSE (byte-read): gcc schedules the arg->pseudo entry copies as ordinary in-block
insns and hoists an unconstrained one to the earliest slot. Mine raced `move $s4,$a0` to
idx 2, which freed $a0 to become the early load temp (target: $v1) and left the target's
idx-12 load-delay slot unfilled. The "wrong temp reg", the mirrored `sw $sN`/`move $sN`
prologue and the +1 instruction were ONE defect in three costumes.
- THE LEVER (cookbook §67, written in-session per R30): an UNPINNED launder
`__asm__ __volatile__("" : "=r"(pv) : "0"(p));` placed at the statement where the target's
copy lands, later uses rewritten to pv. Zero instructions. Prerequisite: collapse redundant
pointer aliases first (the two-pseudo split made gcc serve the first use from the incoming
arg reg). Placement is the knob and is NOT linear -- sweep 3-4 anchors (3-statement plateau).
- 25 -> 16 by reading; permuter_ils (REGALLOC, 10x180s) 16 -> 14 in cycle 1 then x9 unchanged
(§66d-3: a repeat means stop). Its edit is semantics-preserving (hoists desc.y+0x10) and
cleared the idx 271/272 cluster. Seeds tracked: s18_func_8014D820_close{16,14}.c.
- MEASURED NEGATIVES recorded so they are never re-bought: pinning the laundered var to $s4
(pre-stages via $t0, 305 ins); pinning the reused temp t to $3 (287/303); an artificial
"r"(t) dependency (inert -- gcc still hoists); laundering after the beqz (305); dropping the
a2 pin (29); wholesale pos/desc reorder or sinking z0=ent->z (+1 ins).
- NOT banked (G3) -- residual 14 in 2 clusters: idx 21/22 scratch $v1 vs $a0, idx 84-98 the
desc.y/currentLocationId schedule. SCHEDULE-weighted ILS running from the close=14 seed.
- Also measured: func_80140958 260/260 54 - func_80176734 371/371 56 - func_80176218 328 vs
327, whose +1 is NOT §67 (it hoists a global address into an extra callee-saved $s6 that the
target rematerializes -> the §17 array-decay lever).