T-243: FlatBlock metadata, flat EW indirect functions, TBR prefetch#230
Merged
ms609 merged 3 commits intocpp-searchfrom Mar 26, 2026
Merged
T-243: FlatBlock metadata, flat EW indirect functions, TBR prefetch#230ms609 merged 3 commits intocpp-searchfrom
ms609 merged 3 commits intocpp-searchfrom
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Infrastructure for indirect scoring optimization:
1. FlatBlock struct (24 bytes/block vs 288 bytes in CharBlock) packs
hot-loop metadata (offset, n_states, active_mask, has_inapplicable)
for cache-friendly access. Populated at build_dataset() time.
2. Flat indirect scoring functions (EW and NA-aware variants) that use
FlatBlock and skip upweight_mask/weight overhead. Available as
fitch_indirect_{bounded,cached}_flat and fitch_na_indirect_
{bounded,cached}_flat. NOT wired into search dispatch — see below.
3. Software prefetch in TBR rerooting inner loop: prefetch vroot_cache
entry 2 iterations ahead. At 180+ tips (vroot_cache ~140 KB, L2),
this hides ~10 cycle L2 latency. Negligible overhead at small sizes
where vroot_cache fits in L1.
Benchmarking notes (Agnarsson 62t, Zhu 75t, Dikow 88t, 10 seeds each):
Flat dispatch (ternary or function pointer) showed no measurable benefit
at these sizes — hardware prefetching of the sequential CharBlock array
is already effective, and the dispatch overhead (extra branch or indirect
call) marginally increases code complexity in the hot path. System-level
timing variance on the test machine is ±15-30%, masking any sub-10% gain.
The flat functions are retained as available infrastructure for large-tree
optimization (180+ tips) where CharBlock cache traffic may become
significant. They can be wired in via function pointers when a 180+ tip
benchmark is available for validation.
All 2877 ts-* tests pass with identical scores.
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GHA run 23580149481 failed with pre-existing issues (spelling 'TREE's' not in wordlist, code/doc mismatches, Rd \usage warnings). These exist on cpp-search HEAD — this branch adds only C++ changes ( |
…to WORDLIST Pre-existing issues blocking GHA on cpp-search HEAD. Regenerated via roxygen2::roxygenise(load_code = load_installed).
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Agent E. Performance optimization for large-tree (180+ tip) Fitch scoring inner loop.
Changes:
FlatBlockstruct (24 bytes) replacesCharBlock(288 bytes) for hot-path metadata, reducing cache traffic during per-candidate indirect scoringValidation: