Joshua RichterandClaude Opus 5 b04f54506a perf(coverage): find a line by table lookup, not by rescanning the file (#963) ...

cbm_refine_regions_with_pp_lines asks cbm_line_is_toplevel_macro_call about
every preprocessor-parsed line in a region. That check walked the source from
byte 0 to find the line, so the refinement cost bytes times lines — on exactly
the whole-file-ERROR C shape the refinement exists to narrow.

Build one line-offset table per file, and hand the byte span to the macro
check. The line-based form stays for the two callers that ask about a whole
region, where a single walk is cheaper than a table. A file with no table (the
allocation failed) still gets the old walk, so the answer never changes.

Measured on one C file whose file-scope brace is split by an #ifndef, padded to
5k / 10k / 20k / 40k lines. Release build, one machine, seconds:

  lines     main   branch   this commit
   5000     0.98     1.14     0.98
  10000     3.30     4.02     3.41
  20000    11.64    14.77    12.56
  40000    44.04    58.58    46.90

The branch ran 33% over main at 40k lines and now runs 6.5% over. The reported
ranges do not change: 8-8, where main reports the whole file as 5-40000.

A profile of the 40k run no longer reaches the macro check. What is left is
cbm_line_contains and cbm_span_contains_callable_def, which main carries too
and this branch does not touch. The fixture holds 40k definitions, which makes
those two cost more here than on a smaller file.

parse_coverage, extraction, pipeline, mcp and index_resilience: 964 passed,
4 skipped.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Signed-off-by: Joshua Richter <jrichter5781@gmail.com>

2026-09-05 16:24:25 -04:00

..

cbm

perf(coverage): find a line by table lookup, not by rescanning the file (#963)

2026-09-05 16:24:25 -04:00