D7411: dirs: resolve fuzzer OOM situation by disallowing deep directory hierarchies

[durin42 (Augie Fackler)]

durin42 added inline comments.
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INLINE COMMENTS

> indygreg wrote in dirs.c:66
> What code calls this function? Do we have any good perf numbers for introducing this loop?
> 
> I ask because the diffing code is surprisingly impacted by the the "find newlines" stage. Using an implementation that the compiler can expand to SSE/AVX instructions is substantially faster. FWIW glibc and other C implementations have assembly versions of `strchr()` and `memchr()`, which could be substantially faster if the compiler isn't smart enough to detect the "count occurrences of chars" pattern.

I'd be happy to use memchr()  but it occurred to me as I was failing to use memchr() effectively that we already find slashes in a loop here, and there's no risk of on-disk corruption so we can just count slashes as we populate the dict and stop. It's not nearly as fast in the fuzzer, but it does pass for the specific input that we're stuck on.

REPOSITORY
  rHG Mercurial

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  https://phab.mercurial-scm.org/D7411/new/

REVISION DETAIL
  https://phab.mercurial-scm.org/D7411

To: durin42, #hg-reviewers
Cc: indygreg, mercurial-devel