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<regex>: Skip initial NFA nodes that do nothing during matching#6026
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StephanTLavavej merged 1 commit intoJan 20, 2026
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StephanTLavavej
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Jan 18, 2026
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I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed. |
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The NFA generated by the parser always starts with two nodes of type
_N_beginand_N_capturefor capturing group 0. However, the matcher does nothing when it encounters these nodes.While we cannot avoid generating these nodes in the first place (see #6025), this PR skips these nodes during matching to avoid the comparatively expensive (and, in the case of
regex_search(), potentially repeated) processing of these two nodes by the NFA interpreter.The improvement vanishes in the noise in the regex_match benchmark on my machine (it probably saves about 5 ns per match and that is just too little), but it is noticeable in the regex_search benchmark (especially in those examples where regex matching is attempted in many different positions in the string).