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regexp: speed up onepass prefix check #48892
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Remove an unnecessary check that the first operation matches - we know from compile-time that it is EmptyBeginText which will always match at position 0. This enables the call to i.hasPrefix to be done before unpacking the instruction or the first two runes. If the prefix does not match we go straight to return, and if it does match we need the runes after the match, so in either case unpacking the runes was unnecessary.
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This PR (HEAD: d63b833) has been imported to Gerrit for code review.
Please visit https://go-review.googlesource.com/c/go/+/354909 to see it.
Tip: You can toggle comments from me using the comments slash command (e.g. /comments off)
See the Wiki page for more info
717r
commented
Oct 24, 2021
- [ ]
Remove an unnecessary check that the first operation matches - we know
from compile-time that it is EmptyBeginText which will always match at
position 0.
This enables the call to i.hasPrefix to be done before unpacking the
instruction or the first two runes. If the prefix does not match we
go straight to return, and if it does match we need the runes after the
match, so in either case unpacking the runes was unnecessary.
Fixes #48891
Modifying the regexp in BenchmarkAnchoredLiteralShortNonMatch to "^zbc(d|e).*$"
so it uses the onepass engine (see #48748), we get this improvement: