gh-148762: Speed up multiline regexes anchored by ^#152339
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Signed-off-by: Harmen Stoppels <harmenstoppels@gmail.com>
Signed-off-by: Harmen Stoppels <harmenstoppels@gmail.com>
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Multiline regexes of the form
re.compile("^foo", re.MULTILINE)currentlyfall into the generic search loop, which calls
SRE(match)at everyposition in the subject string. Since a
^-anchored (SRE_AT_BEGINNING_LINE)pattern can only match at the start of the string or right after a linebreak,
we can instead jump from one line start to the next, skipping all the
intermediate positions.
Benchmarks show good improvements in runtime across UCS-1/2/4; full
numbers are in the issue.
^. #148762