feat(vcr-ra): ship immediate-shift folding default-on — v0.15.0 (#390, #242)#467
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…#242) Flips the immediate-shift folding peephole default-on (PR #463 landed it flag-off). A constant shift amount the stack selector materialized into a scratch register (`movw rM,#C; lsl rD,rN,rM`) now folds to the immediate form (`lsl rD,rN,#C`), removing the dead `movw` — −1 instruction, −1 live register per folded shift. Flip: arm_backend.rs default-ON with opt-out SYNTH_NO_IMM_SHIFT_FOLD=1. Re-froze the ARM goldens (control_step 316→304, flight_seam 866→774, flight_seam_flat 1006→910 = −200 B; signed_div_const unchanged — no register-shift folds). RV32 gate untouched (ARM-only peephole). Results preserved across the byte change: control_step 0x00210A55 (differential 13/13), flat+inlined flight_algo 0x07FDF307 (MATCH); opt-out restores the v0.14.0 bytes; full workspace suite green. Validated bit-identical + a net cycle win on the dissolved hot path (−2 cyc/call, .text 100→90 B on gust_mix). Cumulative dissolved hot-path: 64.0 → 58.0 (cmp→select) → 50.0 (local promotion) → 48.0 cyc/call. Pin-swept 0.14.0→0.15.0; CHANGELOG added. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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What
Flips the immediate-shift folding peephole default-on (PR #463 landed it flag-off, gate now cleared). A constant shift amount the stack selector materialized into a scratch register (
movw rM,#C; lsl rD,rN,rM) folds to the immediate form (lsl rD,rN,#C), dropping the deadmovw— −1 instruction, −1 live register per folded shift.Re-froze ARM goldens
control_step 316→304, flight_seam 866→774, flight_seam_flat 1006→910 (−200 B); signed_div_const unchanged (no register-shift folds). RV32 gate untouched (ARM-only peephole).
Validation (results preserved)
0x00210A55differential 13/13; flat+inlined flight_algo0x07FDF307MATCH.SYNTH_NO_IMM_SHIFT_FOLD=1) restores the v0.14.0 bytes; full workspace suite green; fmt/clippy/pin-sweep clean..text100→90 B on gust_mix).Cumulative dissolved hot-path: 64.0 → 58.0 (cmp→select) → 50.0 (local promotion) → 48.0 cyc/call.
Pin-swept 0.14.0→0.15.0; CHANGELOG added.
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