test(vcr-ra): shadow allocator vs recovery ladder — spurious vs genuine spill (#242)#479
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…ne spill (#242) Measure-only (SYNTH_SHADOW_ALLOC, byte-identical) — answers the VCR-RA acceptance question empirically: do the recovery ladder's spills survive under a verified (virtual-register) allocator? Running the graph-colouring shadow allocator on the ladder-firing functions splits them: control_step.wasm spill -> shadow peak 8 <= 9 SPURIOUS (VCR-RA subsumes) high_pressure_i32 spill -> shadow peak 10 > 9 GENUINE (VCR-RA spills too) promotion_exhaustion_fallback spill -> shadow peak 10 > 9 GENUINE high_pressure_i64 / msgq_put -> shadow declines (i64/calls — model scope gap) Key result: control_step — a SHIPPED frozen fixture — spills only as a physical-register artifact (its 8 live values fit the 9-wide pool once allocated virtually), exactly the case a verified allocator removes. The genuine floor is the peak-10 functions, where VCR-RA's bar is "spill no worse," not "no spill." Adds the measured comparison to the recovery-ladder map + the CI test shadow_alloc_spurious_vs_genuine_spill_242 (pins the ≤9 / >9 threshold, not exact peaks, so codegen drift won't flap it). No production code changed; frozen gate green. Refs #242 Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Measure-only (
SYNTH_SHADOW_ALLOC, byte-identical — frozen gate green). Answers the VCR-RA acceptance question empirically: do the recovery ladder's spills survive under a verified (virtual-register) allocator?Running the graph-colouring shadow allocator (the VCR-RA prototype) on the ladder-firing functions splits them:
control_step.wasmhigh_pressure_i32promotion_exhaustion_fallbackhigh_pressure_i64,msgq_put_359Key result:
control_step— a shipped frozen fixture (0x00210A55) — spills only as a physical-register artifact (its 8 live values fit the 9-wide pool once allocated virtually), exactly the case a verified allocator removes. The genuine floor is the peak-10 functions, where VCR-RA's bar is "spill no worse," not "no spill." The i64/call decline is the shadow model's TODO, not an allocation result.Adds the measured comparison to
register_exhaustion_recovery_ladder.md+ the CI testshadow_alloc_spurious_vs_genuine_spill_242(pins the ≤9 / >9 threshold, not exact peaks). No production code changed.Refs #242
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