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perf(gust): synth 0.38.0 SYNTH_SHIFT_MASK_ELIDE — gust_mix 1.69×→1.50× (the lever gale filed shipped) - #159
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…69×→1.50× synth 0.38.0 ships the mask-elision lever gale filed (synth#686/#692, `SYNTH_SHIFT_MASK_ELIDE`, flag-off): it elides #682's mod-32 `AND rm,#31` shift mask where the amount is provably <32 — exactly gale's gust_mix (Q8 constant shifts). Re-dissolved cm3+cm4 with the flag: fn-only 0.675 → 0.600 ticks/call (−11%), .text 82 → 68 B (−17%), ratio vs native LLVM 1.69× → 1.50× — best measured on the shipped path. Correctness-gated: gust_floor_bench soundness `mix_proven ≡ mix_native ≡ gust_mix` over [524,1524] PASSES; proof-carrying floor still 0.45×; in-range dissolved 1.55× → 1.40×. silicon_bench links cleanly for thumbv7em. NOTE: the relocatable .o grew 432 → 496 B despite the smaller .text — that's 0.38.0's new ELF metadata (#656 STB_LOCAL internal symbols + #637 .ARM.attributes), dropped/merged at link time, so flash footprint tracks the 68 B .text. 0.38.0 DEFAULT (flag-off) is perf-neutral (1.69×, .text 82) — the release adopt is safe; the win needs the flag. build.rs recipe updated. Ladder: 1.81× (stale) → 1.69× (0.37.1, #157) → 1.50× (0.38.0 elide) → 0.45× (clamp-elision floor, synth#494 phase-2). Reporting the measured 1.50× to synth#686 as the arc toward default-on. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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What
synth 0.38.0 ships the mask-elision lever gale filed (synth#686 → #692,
SYNTH_SHIFT_MASK_ELIDE, flag-off) — eliding #682's mod-32AND rm,#31shift mask where the amount is provably<32, exactly gale'sgust_mix(Q8 constant shifts). Re-pin cm3+cm4 with the flag.Measured (gust_codegen_bench, qemu -icount)
.text(gust_mix)−11% cycles, −17%
.text. Best measured dissolved-vs-native on the shipped path — the ladder is now 2.81× → 2.63× → 1.81× → 1.69× → 1.50× (floor target 0.45×).Correctness gates (all pass)
gust_floor_benchsoundnessmix_proven ≡ mix_native ≡ gust_mixover [524,1524] — sound.silicon_benchlinks cleanly forthumbv7em-none-eabi..text82) — verified; the win needs the flag.Note on
.osizeThe relocatable
.ogrew 432 → 496 B despite the smaller.text— that's 0.38.0's new ELF metadata (#656 STB_LOCAL internal symbols + #637.ARM.attributes), which the linker drops/merges. Flash footprint tracks the 68 B.text, not the.o.Scope: two
gust_mixobjects + COMPARE.md + build.rs recipe. Reporting the measured 1.50× to synth#686 as the arc toward default-on.🤖 Generated with Claude Code