https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62077
--- Comment #41 from rguenther at suse dot de <rguenther at suse dot de> --- On Fri, 15 Aug 2014, sven.c.dack at virginmedia dot com wrote: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62077 > > --- Comment #40 from Sven C. Dack <sven.c.dack at virginmedia dot com> --- > I ran benchmarks and got some unusual results. Or perhaps it is a regression? > > I have created 4 versions of gcc and used these to timed the time it takes to > compile a linux kernel. The configuration of the 4 gcc's are: > > CFLAGS='-pipe -O2 -march=native -fomit-frame-pointer -fno-builtin-memcmp' > > default: > configure ... > make bootstrap > > profiled: > configure ... > make profiledbootstrap > > lto: > configure ... --with-build-config=bootstrap-lto > make bootstrap > > lto-plugin: > configure ... --with-build-config=bootstrap-lto > --with-boot-ldflags="-fuse-linker-plugin" > make bootstrap > > The results are the averages (and deviations) of 5 runs with each compiler: > > avg stdev % > default: 282.86s 0.56s, 0.20% 100.00% (base) > profiled: 255.76s 0.72s, 0.28% +10.60% > lto: 282.80s 0.16s, 0.06% +0.02% > lto-plugin: 285.41s 0.49s, 0.17% -0.89% > > The file sizes of the cc1's are: > > default: 84920k > profiled: 90176k > lto: 71204k > lto-plugin: 60024k > > So boot strapping with LTO does not make gcc faster, but only smaller and also > takes more time. It is almost as if I had used -Os (and not -O2). Most interesting is bootstrap-lto and make profiledbootstrap. > With the linker plugin enabled does it actually link libgcc_s.so and > libstdc++.so dynamically to it, while for the other three it did not: That looks odd. Btw, -fuse-linker-plugin should be the default if you have recent enough binutils. Richard
