[not2b]

There are some very wrong-headed warning options in gcc, such that turning them on and avoiding getting them will make your code worse. So -Wall means 'all recommended warnings'.

Also there are some warnings that won't be produced if you compile without optimization, because the needed analysis isn't performed.

[account42]

And yet we have things like -Wmaybe-uninitialized in -Wall which by definition will occasionally warn on perfectly good code.