BFM-decomp/cookbook/C0434.md

§393 ★★ — THE BIRTHING BOOST: A SINGLE-SET LOCAL IS SCHEDULED LAST; GIVE IT A SECOND SET (P31 S69; byte-proven ov_SC02_017/func_8017FCFC)

A pointer local assigned exactly once (p = D_8018E204;) receives gcc-2.7.2's maximum scheduling priority, and because sched2 works BACKWARD that pushes it LATE — emitting lui/addiu $s1 after the jal where the target has it before. Five instructions of residual, invariant under statement order.

The lever: a zero-byte re-tie in a later block gives the pseudo a SECOND set and kills the boost:

__asm__("" : "=r"(p) : "0"(p));     /* non-volatile, zero bytes, p is now 2-set */

This is the scheduler-side sibling of §380 (a second set disqualifies a pseudo from move_movables). Same one-line trick, two different passes, opposite symptoms: §380 un-hoists a loop invariant, §393 un-delays a preheader constant. If a single-assignment local lands on the wrong side of a call, try the re-tie before reaching for a register pin.