[fgimian]

Thanks so much for your comment. I had actually tried -O3 during my tests and didn't notice a huge difference in this particular example.

fots ~ $ gcc -O -o fib fib.c

fots ~ $ time ./fib

433494437

real 0m0.749s

user 0m0.743s

sys 0m0.003s

fots ~ $ gcc -O3 -o fib fib.c

fots ~ $ time ./fib

433494437

real 0m0.747s

user 0m0.742s

sys 0m0.003s

fots ~ $ gcc -O2 -o fib fib.c

fots ~ $ time ./fib

433494437

real 0m0.741s

user 0m0.737s

sys 0m0.003s

Clearly this is just a little mathematical algorithm and more real-world problems would likely produce a more dramatic difference.

What sort of differences did you see on your end?

[lallysingh]

How much optimization do you expect a loop with a simple addition to have? It doesn't seem a representative workload for an optimizer.

[rdc12]

Except it is not a loop[1], but a non-tail recursive function (with dual calls), if the compiler can optimise that to a loop that is actually impressive.

Most likely function call overhead (and in the slower cases, interpreter overhead) is probably what is being measured in the best case.

[1] In that it won't be a jump and check style loop.

[mbel]

> Most likely function call overhead

Quite likely: https://godbolt.org/g/xGkCyA although it really depends on the compiler (gcc is smarter here). He also seems to be benchmarking printing more than anything else (hence the difference between C and C++).

Without versions of the compilers and explained methods of measurement, the results posted on the blog are more anecdotal knowledge than any kind of benchmark.