From the S76 Fable agent on func_800226C0 — 670 instructions, the largest
function in the project, matched at closeness 0.
Explains WHY pins so often hurt, completing the arc of §461/§462/§471:
(a) A pinned hard register carries no nonzero_bits, so combine cannot fold
sext(HImode t) into a copy — which is exactly what the target's 228E4
addu/beqz/addu chain is, with cse2 reusing it as the loop multiplier.
The $18 pin that looked obvious was what prevented the fold; one plain
uninitialised s16 t (mul left an unpinned pseudo) unlocked it.
(b) A pin makes reg_n_sets != 1, so birthing_insn_p refuses the §199-A
boost and the value is placed first — a whole-block schedule shift.
Unpinning o/col/sh23/abr fixed the prologue order and two ties.
Rule: if a residual involves a sign/zero-extend fold or a first-in-block
placement, REMOVE pins before adding them.
Drew T
920f8bac35