[gnulinux]

I still need evidence that my real time trading app running an entire gcc in it makes it faster. I have no problem with JIT in theory, everything you say makes sense. I've never seen this trend in practice though. Either the optimizations you're talking about can be utilized too rarely, or they are too complex that most JITs don't implement, or they're too expensive that it doesn't give any net gain.

[zzzcpan]

Well, it doesn't actually make sense in theory. While JIT theoretically can profile a current run it also adds a JIT related runtime overhead. It needs to waste a lot of resources on both profiling and recompilation to make use of any new information. That's always going to be strictly slower than PGO techniques, with basically hand picked optimizations for each application and zero overhead.