Strange optimization results

[Jonathan Wakely]

2011/4/10 Дмитрий Оксенчук:
> I have tested performance of std::string compare methods and get
> strange results. With -O2 optimization std::string::compare 30 times
> faster then operator==. With -Os optimization operator== 5 times
> faster then std::string::compare. Is this bug or feature?
>
> Full table (time for 10000000 comparisons in seconds):
>                        -O0             -O1             -O2             -O3             -Os
> compare         1.069   1.057   0.029   0.025   1.072
> operator==      0.461   0.990   0.980   1.022   0.201

Did you run the tests more than once and average the results? Your
test code has no timing measurements in it, what are you measuring?
The entire time for the executable to run?  That includes time for the
OS to create and run a new process, and will depend how busy the
system is, so could have very little to do with the code in the
executable.