link time optimization issue

[Henrik Juul Pedersen]

Hi,

I've been experimenting with link time optimization with GCC, and have
run into an issue with some existing code:

== Test scenario ==
- foo.c:
int foo ( void ) {
    return 3;
}

- bar.c:
#include <stdio.h>

int foo( void );

int main ( void ) {
    printf("Foo returns: %d\n", foo());
    return 0;
}

== Compilation ==
gcc -flto -O2 -c foo.c
ar rcs libfoo.a foo.o
gcc -flto -O2 -L. bar.c -lfoo -o myprog
/tmp/ccGcDjka.ltrans0.ltrans.o: In function `main':
ccGcDjka.ltrans0.o:(.text+0x5): undefined reference to `foo'
collect2: error: ld returned 1 exit status

However, if I directly include the foo object file:
gcc -flto -O2 bar.c foo.o -o myprog

The program links correctly.

== GCC version ==
$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-unknown-linux-gnu/4.9.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: /build/gcc/src/gcc-4.9-20140507/configure
--prefix=/usr --libdir=/usr/lib --libexecdir=/usr/lib
--mandir=/usr/share/man --infodir=/usr/share/info
--with-bugurl=https://bugs.archlinux.org/
--enable-languages=c,c++,ada,fortran,go,lto,objc,obj-c++
--enable-shared --enable-threads=posix --with-system-zlib
--enable-__cxa_atexit --disable-libunwind-exceptions
--enable-clocale=gnu --disable-libstdcxx-pch --disable-libssp
--enable-gnu-unique-object --enable-linker-build-id
--enable-cloog-backend=isl --disable-cloog-version-check --enable-lto
--enable-plugin --enable-install-libiberty
--with-linker-hash-style=gnu --disable-multilib --disable-werror
--enable-checking=release
Thread model: posix
gcc version 4.9.0 20140507 (prerelease) (GCC)

==

Am I missing something? or is this a bug?
I've tried to enable different verbosity settings in compiler and
linker, but have been unable to find any clear reason for the error.

Regards
Henrik
LIAB ApS