Byte-proven on ov_SC01_000/func_8017DD04 (297 ins). Pinning the 0x80 constant to $7
loses its sched1 birthing boost, because $a3 and $a2 are ALSO set by the function's own
call-argument copies (reg_n_sets == 2) - a hard-register pin on an argument register is
unavailable to any function that passes arguments in it.
So win the ranking instead. local-alloc ranks by refs/live_length: 0x80 scored
13/319 = 4890 and took $6 (a pure $a2<->$a3 swap, 24 wrong). One six-input zero-byte
asm on mlo at the blk3/blk4 boundary buys 6 references, 5217 > 4890, mlo takes $6 and
0x80 falls to $7 with its boost intact. The boundary must be the one cut no hoisted
constant crosses, or you move the live lengths you are exploiting.
Measured inert: pinning mlo to $6 (cse never substitutes a hard reg for a bitfield
constant), and a dead hard-reg copy as a register suggestion (flow deletes it).
Drew T
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