Re: [boost] [xpressive] Performance Tuning?

Subject: Re: [boost] [xpressive] Performance Tuning?
From: John Bytheway (jbytheway+boost_at_[hidden])
Date: 2009-07-19 15:15:35

Joel de Guzman wrote:
> John Bytheway wrote:
> 
>> string::begin() return a non-const reference?), but anyway.  Here are
>> the icc results (Intel Core2 Quad 2.83GHz, Gentoo):
>>
>> Loop count:  10000000
>> Parsing:  42.5
>> xpressive:  4.28591
>> spirit-quick(static):  1.4721
>> spirit-quick_new(threadsafe):  1.46949
>> spirit-grammar(threadsafe/reusable):  1.59846
>>
>> and gcc-4.4.0:
>>
>> Loop count:  10000000
>> Parsing:  42.5
>> xpressive:  3.62948
>> spirit-quick(static):  1.02657
>> spirit-quick_new(threadsafe):  1.00637
>> spirit-grammar(threadsafe/reusable):  1.01748
>>
>> gcc 4.3 is still ICEing.
> 
> Those are good numbers. It shows that the effect of the
> virtual function call of the spirit grammar rules is obviated
> out of existence!
> 
> For the record, this one shows the xpressive code using spirit
> numeric parsers to convert the string to numbers, right?

Correct.

> Will the original OP please (PLEASE!) come forward and post his
> original hand-coded program? This is SOOO confusing!

Well, in case he doesn't, I've thrown together an implementation of
core::to_number based on Robert's description of it.  I had to guess at
the interface, and I didn't verify correctness.  I also had to implement
two error routines; I made them both "throw 0;".

I also tweaked the xpressive code so that it didn't copy the sub_match
objects to strings before using qi to parse out the doubles and ints.
That sped it up slightly (gcc 4.4.0 again):

Loop count:  10000000
Parsing:  42.5
original-custom:  2.08637
xpressive:  2.94329
spirit-quick(static):  1.02784
spirit-quick_new(threadsafe):  1.03306
spirit-grammar(threadsafe/reusable):  1.00213

although I'm slightly concerned with what happened when I changed the
string to be parsed:

Loop count:  10000000
Parsing:  425/500
original-custom:  1.6307
xpressive:  116.992
spirit-quick(static):  0.552722
spirit-quick_new(threadsafe):  0.53429
spirit-grammar(threadsafe/reusable):  0.680257

Why is the xpressive code so slow here?  The parsing is more complex in
this case, but I wouldn't think it was this bad!  Perhaps I broke it
somehow...

New code attached (also includes other minor changes I had to make to
get things to compile).

If someone writes core::numeric_cast then the 'original' xpressive code
can be used.

John Bytheway