Working with PGO
In the previous section, we learned how a sanitizer assists developers in performing sanity checks with higher precision using data that is only available at runtime. We also learned how to create a custom sanitizer. In this section, we will follow up on the idea of leveraging runtime data. We are going to learn an alternative use for such information – using it for compiler optimization.
PGO is a technique that uses statistics that have been collected during runtime to enable more aggressive compiler optimizations. The profile in its name refers to the runtime data that's been collected. To give you an idea of how such data enhances an optimization, let's assume we have the following C code:
void foo(int N) {
  if (N > 100)
    bar();
  else
    zoo();
}
In this code, we have three functions: foo, bar, and zoo. The first function conditionally calls the latter two.
When we...
