[Bug lto/56700] New: Optimizing at compile and link result in different binary size than only optimizing at link time

[uran238 at web dot de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56700



             Bug #: 56700

           Summary: Optimizing at compile and link result in different

                    binary size than only optimizing at link time

    Classification: Unclassified

           Product: gcc

           Version: lto

            Status: UNCONFIRMED

          Severity: normal

          Priority: P3

         Component: lto

        AssignedTo: unassig...@gcc.gnu.org

        ReportedBy: uran...@web.de





When I'm building wget (1.14) with CFLAGS=LDFLAGS="-Os -flto" the resulting

binary is about 5-8% smaller than building with CFLGAS="-flto" LDFLAGS="-Os

-flto".



Adding -fno-fat-lto-objects leads to very similar results (~50 Bytes

difference).



Here are the (stripped) sizes:

CFLAGS=-Os LDFLAGS=-Os

gcc-4.7.2: 353904

gcc-4.8.0: 349808



CFLAGS=-O0 -flto LDFLAGS=-Os -flto

gcc-4.7.2: 353408

gcc-4.8.0: 360696



CFLAGS=-Os -flto LDFLAGS=-Os -flto

gcc-4.7.2: 336896

gcc-4.8.0: 332784



So not optimizing for size during compile leads to worse results than omitting

lto at all for gcc-4.8



I thought optimizations can be ommitted completely during compile, when doing

lto.