Replacing QRegExp with CMake RegularExpression

[Robert Knight]

Hi,

> That's an impressive difference.

Assuming you're testing with an optimized build of Qt that difference
surprises me, what is taking the extra time in QRegExp?

Regards,
Robert.

2008/11/2 M Breugelmans <mbr.nxi at gmail.com>:
> On Sun, Nov 2, 2008 at 2:59 AM, Andreas Pakulat <apaku at gmx.de> wrote:
>> Hi,
>>
>> so I thought it might be interesting to try this out. Turned out to be a
>> bit more complex than I initially thought and unfortunately it also
>> introduces one regression with the kde4addunittest test. (I'm seeing an
>> error message from RegularExpression about nested "*?+", so that might be a
>> hint).
>
> Weird, that test still runs fine for me after applying your patch.
>
>> Having done a quick time kdevelop like test the startup speed of kdevelop
>> including loading of kdevplatform was reduced frmo 15 to 11 seconds on my
>> old machine.
>
> That's an impressive difference.
>
>> The patch is attached for anyone to look at, whats a bit scary is the
>> conversion between QString and char* for the RegularExpression class. I'm
>> actually thinking about seeing wether converting to QChar helps with that
>> or wether using that class drains performance again.
>>
>
> Constructing RE's is typically expensive, depending on the pattern it
> can cost as much as a search. QRegExp actually caches compiled RE's
> behind the scenes (it's #if-deffed though, I did not check if it's
> enabled), but the cmake one for sure doesn't.
>
> Next to the performance gain using kitware's implementation would
> guarantee 100% identical behavior.
>
>
> Manuel
>
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