match with regex_constants::match_any bug


In multiple overloads of regex_match, regex_constants::match_any is enabled by default, which can cause a drastic drop in matching performance (by a factor of tens to hundreds). This appears to be a bug in either the implementation or the way the function is invoked.

Start at the regex_match overloads and inspect how regex_constants::match_any is enabled by default. Reproduce the reported performance difference, then determine whether the issue is in the implementation or how the function is invoked. Done means the cause is confirmed and matching performance no longer suffers the reported regression.

Written by the indexing model from the issue text.