What information does GCC Profile Guided Optimization (PGO) collect and which optimizations use it?

Question

Which information does GCC collect when I enable -fprofile-generate and which optimization does in fact uses the collected information (when setting the -

Answer 1

-fprofile-generate enables -fprofile-arcs, -fprofile-values and -fvpt.

-fprofile-use enables -fbranch-probabilities, -fvpt, -funroll-loops, -fpeel-loops and -ftracer

Source: http://gcc.gnu.org/onlinedocs/gcc-4.7.2/gcc/Optimize-Options.html#Optimize-Options

PS. Information about LTO also on that page.