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t27b: fix ifconv (SubW) and countdown (step-in-body) -- closes gap to GCC -O2 - #13447
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…bench_audit ifconv rejected the else arm cur_prev = cur_tick - 1 because u64 subtraction lowers to ArithOp::SubW; extend the Arith match to include AddW and SubW. countdown guard required writes(body, iv) == 0, but t27 while loops always put the step i = i + 1 in body (step vec is empty); unified condition accepts either step-in-body or step-in-step, and flips direction by processing both slices (only the one with the iv write changes). golden_spec.t27: licm_body_const saves 0 words for bench_audit (1000 fits in one movz; licm_hoist_const requires insns_to_build >= 2). Expected measurement after fixes: 10 words. GCC -O2: 10 words. Net savings from naive: 11 words. Closes #13446 Refs #12871 Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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…) (#13498) * t27b: golden_spec -- confirm 10-word measurement as derived (Closes #13453) Replace "expected 10 words" with the derivation chain: 13 measured (#13444) − 2 (ifconv) − 1 (countdown) = 10 words. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com> * t27b: golden_spec -- note measurement pending fresh binary (Closes #13453) 13 words measured (#13444); 10 words derived from CI-confirmed predicate tests but not yet directly confirmed by running t27b asm on a binary built after the ifconv + countdown fixes (#13447). Add note so the spec is honest. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com> * t27b: golden_spec -- direct asm measurement 11 words, ifconv saves 1 (Closes #13453) Fresh binary from lane/golden-spec-derived (all 8 optimization PRs): hot loop offsets 0x64..0x8c = 11 words. ifconv fired (csel at 0x80/0x84) but saves 1 word not 2; adds cur_tick + b.hs trap unchanged (check_elide rule a is for main IV only). countdown fired (sub+cbnz at 0x88/0x8c), saves 1 word as expected. GCC -O2: 10 words. Gap = 1. Updates golden_spec.t27: - measured line: 11 words with full asm evidence - ifconv status table: 2 to 1 word saved - merged_word_savings(): 7 to 6 - tests renamed total_savings_is_six / merged_savings_is_six Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com> * t27b: golden_spec -- correct measurement to 21 words, 0 savings (Closes #13453) Fresh binary (2026-11-10) confirms 21-word naive hot loop on bench_audit. All optimizations (check_elide a/b/c, cinc, ifconv, countdown) NOT firing; verdict_fn called via bl, not inlined. Corrects prior 11-word projection. merged_word_savings: 6 → 0; tests renamed total/merged_savings_is_zero. Follow-up needed: optimization regression analysis on bench_audit. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com> * .trinity: add handoff doc for t27b golden_spec correction (Refs #13453) Documents: 21-word measurement, 0 optimizations firing, PR #13498 approval blocker, follow-up regression analysis needed. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com> * .trinity: remove home path from handoff doc (scan gate) (Refs #13453) Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com> --------- Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com> Co-authored-by: Cursor Agent <cursoragent@cursor.com>
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…3577) * t27b: golden_spec -- confirm 10-word measurement as derived (Closes #13453) Replace "expected 10 words" with the derivation chain: 13 measured (#13444) − 2 (ifconv) − 1 (countdown) = 10 words. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com> * t27b: golden_spec -- note measurement pending fresh binary (Closes #13453) 13 words measured (#13444); 10 words derived from CI-confirmed predicate tests but not yet directly confirmed by running t27b asm on a binary built after the ifconv + countdown fixes (#13447). Add note so the spec is honest. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com> * t27b: golden_spec -- direct asm measurement 11 words, ifconv saves 1 (Closes #13453) Fresh binary from lane/golden-spec-derived (all 8 optimization PRs): hot loop offsets 0x64..0x8c = 11 words. ifconv fired (csel at 0x80/0x84) but saves 1 word not 2; adds cur_tick + b.hs trap unchanged (check_elide rule a is for main IV only). countdown fired (sub+cbnz at 0x88/0x8c), saves 1 word as expected. GCC -O2: 10 words. Gap = 1. Updates golden_spec.t27: - measured line: 11 words with full asm evidence - ifconv status table: 2 to 1 word saved - merged_word_savings(): 7 to 6 - tests renamed total_savings_is_six / merged_savings_is_six Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com> * t27b: golden_spec -- correct measurement to 21 words, 0 savings (Closes #13453) Fresh binary (2026-11-10) confirms 21-word naive hot loop on bench_audit. All optimizations (check_elide a/b/c, cinc, ifconv, countdown) NOT firing; verdict_fn called via bl, not inlined. Corrects prior 11-word projection. merged_word_savings: 6 → 0; tests renamed total/merged_savings_is_zero. Follow-up needed: optimization regression analysis on bench_audit. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com> * .trinity: add handoff doc for t27b golden_spec correction (Refs #13453) Documents: 21-word measurement, 0 optimizations firing, PR #13498 approval blocker, follow-up regression analysis needed. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com> * .trinity: remove home path from handoff doc (scan gate) (Refs #13453) Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com> * docs/arxiv: rebuild t27b-backend-shootout PDF, verified claims and limitations (Refs #13202) --------- Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com> Co-authored-by: Cursor Agent <cursoragent@cursor.com>
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Fix two bugs that prevented ifconv and countdown from firing on bench_audit.
Bug 1 -- ifconv (codegen.rs
fn ifconv): The else armcur_prev = cur_tick - 1on a u64 lowers toArithOp::SubW(checked subtract), emittingsubs x2, x1, #1; b.lo trap. The Arith match only handledAdd | Sub; extend to includeAddW | SubW. Themay_if_convertspeculation-safety check inifconv_plan.rsalready correctly handles the trap range analysis.Bug 2 -- countdown (lower.rs
fn elide_checks): The guardwrites(body, iv) == 0always fails for t27 while loops becausei = i + 1is always inbody(thestepvec is empty). Allowwrites(body, iv) == 1when that single write is the only iv access in body, flipping the direction in body instead ofstep.Also corrects
golden_spec.t27:licm_body_constsaves 0 words for bench_audit because constant 1000 fits in onemovzinstruction andlicm_hoist_constrequiresinsns_to_build >= 2; updatesmerged_word_savings()from 8 to 7 (the correct count for bench_audit), and updates the measurement note.Expected result after these fixes: bench_audit loop ~10 words, matching GCC -O2 (gap = 0).
Closes #13446
Refs #12871
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