Benchmarking C++ Compilers. A Real World Example.

I was curios how different compilers and the optimization options affect the speed of my DNA simulation program scrm. There are almost no hard computations in scrm; the bottleneck when running the program is reading and modifying memory, so there might not be much for compilers to optimize.

I benchmarked the runtime of

scrm 10 10 -r 1000 1000000 -seed 20

using the C++ version of gcc 4.8.2 and clang 3.4 with different optimization levels. The results are:

	g++	clang++
O0	152s	150s
O1	31s	78s
O2	26s	34s
O3	25s	34s

Seems that increasing the optimization level up to O2 really helps on both compilers, and further increasing it to O3 only gives a minor speed boost. On high optimization levels, g++ is about 25% faster than clang++, so using the gcc whenever possible seems to be a good idea.