ÐÐÐÑÑÐÐ ÐÐÑÐÐÑÑÐ <oksenchuk89@xxxxxxxxx> writes: > 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 > > g++ (Debian 4.3.4-6) 4.3.4. Test code attached. It's pretty hard to tell whether this is a bug or a feature in and of itself. -Os optimizes for code size. -O2 optimizes for runtime performance. I don't see any particular reason to expect std::string::compare or operator== to be faster or slower with either one. If you showed that -Os was faster than -O2, or that -O2 was smaller than -Os, then I would say that you have found a bug. However, I would qualify that by asking whether you are using the -march and -mtune options appropriate for the specific CPU on which you are doing the testing. And I would qualify it further by saying that micro-benchmarks are notoriously unreliable when it comes to predicting performace in real code. They are not always wrong, but they often are. Ian
