gcc - What's the best g++ optimization level when building a debug target?

Question

When you want to build something that's debuggable (g++ specifically, but perhaps shares an answer with gcc), what's the best -O level? In other words, when building a "debug" target rather than a "release" target.

The gcc online docs are a little sketchy when comparing -O0 and -O1 (here). My interpretation is that -O1 only enables one optimization that even may affect debugability, which is -fomit-frame-pointer. But to quote the doc, it's only enabled in -O1 "where doing so does not interfere with debugging." Am I interpreting that correctly?

Another post on this site (here) talks about -O2 specifically, and the answer is basically "it works but you get out-of-order execution". Which, IMO, can range from annoying to devastating depending on how badly things jump around.

Answer 1

GCC 4.8 introduces a new optimization level: -Og for the best of both worlds.

-Og
Optimize debugging experience. -Og enables optimizations that do not interfere with debugging. It should be the optimization level of choice for the standard edit-compile-debug cycle, offering a reasonable level of optimization while maintaining fast compilation and a good debugging experience.

This way some optimization is done so you get better performance, better possibly-uninitialized variable detection and you can also step through a program in GDB without jumping back-and-forth through the function.