On Tue, Mar 17, 2020 at 12:22:07PM +0000, Richard Sandiford wrote: > Segher Boessenkool <segher@xxxxxxxxxxxxxxxxxxx> writes: > > 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. > > I think David's the right that the wording isn't clear though. Oh yes, I didn't mean to suggest it is perfect as is, sorry. > The documentation sets up a contrast between an option being "enabled" > or merely "specified", with "enabled" meaning something like "have an > effect". But the quoted output then undermines that by using "enabled" > for what the documentation calls "specified": > > $> gcc -Q --help=optimizers -fmove-loop-invariants | grep "\-fmove-loop-invariants" > -fmove-loop-invariants [enabled] > > I can definitely see why this is confusing. Yeah. Help output is not documentation, but if they aren't in agreement, what is a user to do? :-( Does anyone have proposed improved wording, etc.? Segher
