[Bug other/45996] New: -falign-functions=X does not work

[Bug other/45996] New: -falign-functions=X does not work

[us15 at os dot inf.tu-dresden.de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45996

           Summary: -falign-functions=X does not work
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: other
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: us15@os.inf.tu-dresden.de


According to the gcc manpage, specifying -falign-functions=X should align
functions on an X-byte boundary. This works correctly with 4.1.2, 4.2.4, and
4.3.5. It does not work with 4.4.5, 4.5.1, 4.6.0 (svn) and will instead cause
function aligning to be completely disabled. This can be observed both in
generated code and in gcc --help=optimizers

[Bug other/45996] -falign-functions=X does not work

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45996

--- Comment #1 from Richard Guenther <rguenth at gcc dot gnu.org> 2010-10-13 09:10:05 UTC ---
Works for me.

[Bug other/45996] -falign-functions=X does not work

[us15 at os dot inf.tu-dresden.de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45996

--- Comment #2 from Udo Steinberg <us15 at os dot inf.tu-dresden.de> 2010-10-13 12:06:32 UTC ---
Created attachment 22029
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=22029
Testcase

gcc -Os -falign-functions=32 foo.cc -o foo
nm foo | c++filt | grep func_
00000000004004f6 T func_bar()
0000000000400500 T func_baz()
00000000004004ec T func_foo()

gcc -falign-functions=32 foo.cc -o foo
nm foo | c++filt | grep func_
0000000000400520 T func_bar()
0000000000400540 T func_baz()
0000000000400500 T func_foo()

So it seems to be related to the -Os option. My gcc is configured as follows:

gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-slackware-linux/4.6.0/lto-wrapper
Target: x86_64-slackware-linux
Configured with: ../gcc-svn/configure --prefix=/usr --libdir=/usr/lib64
--enable-shared --enable-bootstrap --enable-languages=c,c++
--enable-threads=posix --enable-checking=release --with-system-zlib
--disable-libunwind-exceptions --enable-__cxa_atexit --enable-libssp
--with-gnu-ld --verbose --disable-multilib --target=x86_64-slackware-linux
--build=x86_64-slackware-linux --host=x86_64-slackware-linux
Thread model: posix
gcc version 4.6.0 20101005 (experimental) (GCC)

[Bug other/45996] -falign-functions=X does not work

[us15 at os dot inf.tu-dresden.de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45996

--- Comment #3 from Udo Steinberg <us15 at os dot inf.tu-dresden.de> 2010-10-13 12:19:57 UTC ---
According to the gcc manpage:

           -Os disables the following optimization flags: -falign-functions
           -falign-jumps  -falign-loops -falign-labels  -freorder-blocks
           -freorder-blocks-and-partition -fprefetch-loop-arrays
           -ftree-vect-loop-version

But this is what actually happens:

gcc -Os -Q --help=optimizers | grep align-functions
  -falign-functions                     [enabled]
gcc -Os -falign-functions -Q --help=optimizers | grep align-functions
  -falign-functions                     [enabled]
gcc -Os -falign-functions=32 -Q --help=optimizers | grep align-functions
  -falign-functions                     [disabled]

[Bug target/45996] -falign-functions=X does not work

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45996

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Target|                            |x86_64-*-*
          Component|other                       |target

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> 2012-01-28 19:17:16 UTC ---
This is a target issue overriding it for -Os.