Profile Guided Optimisation

[Stefan Heimers]

I just read the following in a slashdot discussion:

 by norton_I (64015)
 "Basically, you compile with -fprofile-arcs, run the executable enough
 to generate sufficient data, then compile with -fbranch-probabilities.
 This will try to order basic blocks so that the CPU predicts branches
 correctly most often."

Did anybody try if it works? How much does it help? Can it be done with 
complex projects like KDE?


Stefan