Maintaining Profile up to Date

More delicate task than updating control flow graph is to update profile. Many of the function to modify flow graph, like redirect_edge_and_branch do not have enough information to easily update profile, so updating profile is in majority cases left on the caller. Since it is difficult to discover bugs in the profile updating code, as they manifest themselves only by producing worse code and checking profile consistency is not possible, because of numeric error accumulation, special care needs to be taken into this issue.

It is important to point out, that REG_BR_PROB_BASE and BB_FREQ_BASE are both set low enough to be possible to compute second power of any frequency or probability in the flow graph, it is not possible to even square the count field, as modern CPUs are fast enough to execute $2^32$ operations quickly.