On Mon, 16 Mar 2020 at 23:35, Segher Boessenkool wrote: > > On Mon, Mar 16, 2020 at 11:14:25PM +0000, Shrader, David Lee via Gcc-help wrote: > > Most optimizations are only enabled if an -O level is set on the command line. Otherwise they are disabled, even if individual optimization flags are specified. > > Yes. > > > The man page says to use `-Q --help=optimizers` to find out what is turned on for the different -O levels as configure-time options can make things different from the defaults shown later in that man page. However, I have found that, even when using -O0, I can turn on optimization options, at least according to the help output: > > You can enable the *flags*, sure, but with -O0 those flags do not do > anything. Exactly as the text above says? The "even if" part. See also https://gcc.gnu.org/wiki/FAQ#optimization-options
