Register deprivation: spills and runtime under forced register scarcity

Intel Xeon E-2236 @ 3.40GHz · gcc 15.2.0 · 2026-07-13 We compiled nine small kernels while progressively reserving registers with gcc -ffixed-<reg> , then measured spills and runtime on one machine. Reserving registers reliably increases spills, but the static spill count is a weak predictor of the runtime cost, and one kernel gains 23 spills with no slowdown at all. Code is at…