Re: [PATCH] lto/114655 - -flto=4 at link time doesn't override -flto=auto at compile time

[Richard Biener <rguenther@suse.de>]

On Tue, 9 Apr 2024, Jan Hubicka wrote:

> > The following adjusts -flto option processing in lto-wrapper to have
> > link-time -flto override any compile time setting.
> > 
> > LTO-boostrapped on x86_64-unknown-linux-gnu, testing in progress.
> > 
> > OK for trunk and branches?  GCC 11 seems to be unaffected by this.
> > 
> > Thanks,
> > Richard.
> > 
> > 	PR lto/114655
> > 	* lto-wrapper.cc (merge_flto_options): Add force argument.
> > 	(merge_and_complain): Do not force here.
> > 	(run_gcc): But here to make the link-time -flto option override
> > 	any compile-time one.
> Looks good to me.  I am actually surprised we propagate -flto settings
> from compile time at all.  I guess I never tried it since I never
> assumed it to work :)

We do magic now ;)  I think this was done because while people manage
to use CFLAGS=-flto they eventually fail to adjust LDFLAGS and without
plugin auto-loading you won't get LTO and in particular not -flto=auto.

I checked that it now works as expected - fortunately -v now displays
the make invocation command, so it was easy to verify.

Richard.