Avoid UTF-8 validating same string multiple times #3957
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@dstogov Can you take a look at this? |
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Looks fine to me. |
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This could be a base for solving bug #52998, too. |
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Merged as 2b9acd3 into 7.4. |
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Fix for https://bugs.php.net/bug.php?id=72685.
We currently have a huge performance problem when implementing lexers working on UTF-8 strings in PHP. This kind of code tends to perform a large number of matches at different offsets on a single string. This is generally fast. However, if
/umode is used, the full string will be UTF-8 validated on each match. This results in quadratic runtime.This patch fixes the issue by adding a
IS_STR_VALID_UTF8flag, which is set when we have determined that the string is valid UTF8 and further validation is skipped.A limitation of this approach is that we can't set the flag for interned strings. I think this is not a problem for this use-case which will generally work on dynamic data. If we want to use this flag for other purposes as well (mbstring?) then it might be worthwhile to UTF-8 validate strings during interning. But right now this doesn't seem useful.