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-O3 gained a reputation of being more likely to "break" code, but in reality it was almost always "breaking" code that was invalid to start with (invoked undefi
by sgerenser 11mo ago
-O3 gained a reputation of being more likely to "break" code, but in reality it was almost always "breaking" code that was invalid to start with (invoked undefined behavior). The problem is C and C++ have so many UB edge cases that a large volume of existing code may invoke UB in certain situations. So -O2 thus had a reputation of being more reliable. If you're sure your code doesn't invoke undefined behavior, though, then -O3 should be fine on a modern compiler.
- drob518 11mo agoExactly. A lot of people didn’t understand the contract between the programmer and the compiler that is required to use -O3.
- MaxBarraclough 11mo agoThat's a little vague, I'd put that more pointedly: they don't understand how the C and C++ languages are defined, have a poor grasp of undefined behaviour in particular, and mistakenly believe their defective code to be correct. Of course, even with a solid grasp of the language(s), it's still by no means easy to write correct C or C++ code, but if your plan it to go with this seems to work, you're setting yourself up for trouble.
- uecker 11mo agoOh, there are also plenty of bugs. And Clang still does not implement the aliasing model of C. For C, I would definitely recommend -O2 -fno-strict-aliasing
- afdbcreid 11mo agoIndeed, e.g. Rust by default (release builds) use -O3.