Fix perf bug in RegexCompiler when handling .*?#118373
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stephentoub merged 1 commit intodotnet:mainfrom Aug 5, 2025
Merged
Fix perf bug in RegexCompiler when handling .*?#118373stephentoub merged 1 commit intodotnet:mainfrom
stephentoub merged 1 commit intodotnet:mainfrom
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We have a special-code path that exists to optimize a singleline `.*?`, in which case we can just search for what comes after the loop in the pattern because the loop itself will lazily match everything. Unfortunately, we're passing the wrong node to the EmitIndexOf helper that emits that search. We should be passing the node which represents the subsequent literal, but we're accidentally passing the set loop itself. We're only here if that set loop matches everything, so we're emitting an IndexOfAnyInRange(0, \uFFFF) call. This is functionally ok, but perf tanks because we end up needing to do non-trivial work for every character that matches the loop.
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Pull Request Overview
This PR fixes a performance bug in the regex compiler's optimization for lazy quantifiers followed by literals. The bug occurred when handling patterns like .*? (singleline lazy dot-star) followed by a literal, where the compiler was incorrectly passing the wrong node to the IndexOf emission helper.
- Corrects the node parameter passed to
EmitIndexOffrom the loop node to the literal node - Fixes performance degradation caused by inefficient
IndexOfAnyInRange(0, \uFFFF)calls - Maintains functional correctness while improving performance for this optimization path
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MihaZupan
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Nice. Did you spot this in some benchmark given it's compiler-only?
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Yup, the numbers I was getting out made no sense. |
radekdoulik
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We have a special-code path that exists to optimize a singleline `.*?`, in which case we can just search for what comes after the loop in the pattern because the loop itself will lazily match everything. Unfortunately, we're passing the wrong node to the EmitIndexOf helper that emits that search. We should be passing the node which represents the subsequent literal, but we're accidentally passing the set loop itself. We're only here if that set loop matches everything, so we're emitting an IndexOfAnyInRange(0, \uFFFF) call. This is functionally ok, but perf tanks because we end up needing to do non-trivial work for every character that matches the loop.
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We have a special-code path that exists to optimize a singleline
.*?, in which case we can just search for what comes after the loop in the pattern because the loop itself will lazily match everything. Unfortunately, we're passing the wrong node to the EmitIndexOf helper that emits that search. We should be passing the node which represents the subsequent literal, but we're accidentally passing the set loop itself. We're only here if that set loop matches everything, so we're emitting an IndexOfAnyInRange(0, \uFFFF) call. This is functionally ok, but perf tanks because we end up needing to do non-trivial work for every character that matches the loop.