regalloc_evict_test.nx

regalloc_evict_test.nx -- proves the Poletto-Sarkar spill-at- interval eviction policy fires (added to linear_scan in nx_regalloc.nx). Construction: build 17 long-lived binop values (v0..v16) where v0 has the LATEST use (end ~ 34) and v16 has the EARLIEST use (end ~ 18). With 16 GPRs and 17 live values, exactly one must spill. Without eviction: v16 spills (arrival order -- the latest-arriving interval that finds the pool empty gets demoted). This wastes a spill slot on a short-lived value while a long-lived value (v0) happily keeps its register. With eviction (the new policy): when v16 arrives and pop_free returns -1, spill_furthest_gpr walks active[] (sorted by end ascending) and finds v0 at the back with end=34 > v16.end=18. Since v0.end > v16.end, v0 is evicted and v16 gets v0's register. The assertion: locs[ID_OF_V0].kind == VL_SPILLED. This is the proof the eviction fired -- v0 was the LATEST-end interval and got evicted by the new spill heuristic, not by arrival order.