SqlScan's inner scan was written as a single loop with `if whereFn
!= nil` and a `keep` shadow variable. Branch-predictable for sure,
but still a few extra ops per row and it prevented Go from inlining
the non-nil interface call on the Area branch.
Split into four specialized loop bodies on the two axes that drive
per-row cost:
1. dbfArea != nil && whereFn != nil
2. dbfArea != nil && whereFn == nil ← tightest path (SELECT *)
3. dbfArea == nil && whereFn != nil ← generic Area
4. dbfArea == nil && whereFn == nil
Each body has exactly the instructions it needs — no dead branches,
no shadow variables, no interface dispatch where avoidable. Copy-paste
cost is real but each row save adds up at 50k iterations.
Bench impact (50k rows, 3-run steady state):
No WHERE 9.1ms → 8.7ms 1.38x vs raw (was 1.47x)
Numeric WHERE 6.9ms → 7.0ms ~flat (within noise)
String WHERE 6.2ms → 6.4ms ~flat (within noise)
Raw RDD 6.3ms baseline
Validation:
- FiveSql2 43/43
- Harbour compat 51/51
- go test ./hbrtl/... PASS
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
CharlesKWON
5dd212c761