Better PGO tooling can use the profiles from previous version of the code, which is almost but not quite the same, to compile a PGO optimized build of the patch

Better PGO tooling can use the profiles from previous version of the code, which is almost but not quite the same, to compile a PGO optimized build of the patched version. If there is no tooling to do that, a subset of the training data can be used which can be processed in a short amount of time to gather enough profile data to get most of the benefits. So say, instead of 20% faster code after 6 hours, 10% faster code after 15 minutes. It is also possible to use PGO to find the critical optimizations done in the PGO optimized build that lead to most of the gains and add annotations in the code (branch taken, branch not taken, force inline, never inline, etc) or split functions the way the PGO optimized build does (e.g. common case is inline the guarding if statement at the beginning of the function, not inline the rest of the function).