Like the predecessor change https://crrev.com/c/v8/v8/+/1702125 , this
change is inspired by attempting to exit earlier from generated RegExp
code, when no further matches are possible because any match would be
too long. The motivating example this time is the following expression,
which tests whether a string of Unicode playing cards has five of the
same suit in a row:
/([🂡-🂮]{5})|([🂱-🂾]{5})|([🃁-🃎]{5})|([🃑-🃞]{5})/u
A human reading this expression can readily see that any match requires
at least 10 characters (5 surrogate pairs), but the LoopChoiceNode for
each repeated option reports its minimum distance to the end of a match
as zero. This is correct, because the LoopChoiceNode's behavior depends
on additional state (the loop counter). However, the preceding node, a
SET_REGISTER action that initializes the loop counter, could confidently
state that it consumes at least 10 characters. Furthermore, when we try
to emit a quick check for that action, we could follow only paths from
the LoopChoiceNode that are possible based on the minimum iteration
count. This change implements both of those "could"s.
I expect this improvement to apply pretty broadly to expressions that
use minimum repetition counts and that don't meet the criteria for
unrolling. In this particular case, I get about 12% improvement on the
overall UniPoker test, due to reducing the execution time of this
expression by 85% and the execution time of another similar expression
that checks for n-of-a-kind by 20%.
Bug: v8:9305
Change-Id: I319e381743967bdf83324be75bae943fbb5dd496
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1704941
Commit-Queue: Seth Brenith <seth.brenith@microsoft.com>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62963}
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