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Problem: nfa_regmatch() allocates and frees two list buffers on every
call, causing unnecessary memory allocation overhead for
frequently used patterns.
Solution: Cache the list buffers in the regprog struct and reuse them
on subsequent top-level calls. Recursive calls still allocate
their own buffers. Free cached buffers in nfa_regfree()
(Yasuhiro Matsumoto).
Benchmark: 10K lines, `:%s` x50 iterations
| Pattern | Before | After | Improvement |
|---|---|---|---|
| `\<\(\w\+\%(ing\|tion\|ed\|ly\)\|\w\{3,}\)\>` (many matches) | 4.384s | 4.299s | -2% |
| `\(foo\|bar\|baz\)\{3,}\(qux\|quux\|corge\)\{2,}...` (no match, high nstate) | 16.927s | 3.015s | -82% |
closes: vim/vim#19956
105d65e29b
Co-authored-by: Yasuhiro Matsumoto <mattn.jp@gmail.com>