[Bug lto/63215] New: LTO causes symbols for builtin functions to be omitted from object files

[patrick at motec dot com.au]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63215

            Bug ID: 63215
           Summary: LTO causes symbols for builtin functions to be omitted
                    from object files
           Product: gcc
           Version: 4.9.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: lto
          Assignee: unassigned at gcc dot gnu.org
          Reporter: patrick at motec dot com.au

-flto causes symbols for builtin functions to be omitted from object files.
Specifying -fno-builtin generates the symbols again.

This causes problems when these files are combined into an archive and used for
later linking as the linker can't resolve the symbols.

For example:

abs.c:

int abs(int j)
{
    return j < 0 ? -j : j;
}

Normal compile:

$ powerpc-eabispe-gcc -c abs.c -o abs.o
$ powerpc-eabispe-gcc-nm abs.o
00000000 T abs

Compile with lto:

$ powerpc-eabispe-gcc -flto -c abs.c -o abs_lto.o 
$ powerpc-eabispe-gcc-nm abs_lto.o
/home/patrick/toolchain/lib/gcc/powerpc-eabispe/4.9.1/../../../../powerpc-eabispe/bin/nm:
abs_lto.o: no symbols

Compile with lto and no-builtin:

$ powerpc-eabispe-gcc -fno-builtin -flto -c abs.c -o abs_lto_nobuiltin.o
$ powerpc-eabispe-gcc-nm abs_lto_nobuiltin.o
00000000 T abs

Here is the output of gcc -v

$ powerpc-eabispe-gcc -v
Using built-in specs.
COLLECT_GCC=powerpc-eabispe-gcc
COLLECT_LTO_WRAPPER=/home/patrick/src/e7/toolchain/stage2/libexec/gcc/powerpc-eabispe/4.9.1/lto-wrapper
Target: powerpc-eabispe
Configured with: /home/patrick/src/e7/toolchain/src/gcc-4.9.1/configure
--prefix=/home/patrick/src/e7/toolchain/stage2 --build=x86_64-unknown-linux-gnu
--host=x86_64-unknown-linux-gnu --target=powerpc-eabispe
--enable-languages=c,c++
--with-sysroot=/home/patrick/src/e7/toolchain/../prex_sysroot --disable-nls
--disable-werror --with-newlib --with-gmp=/home/patrick/src/e7/toolchain/stage2
--with-mpfr=/home/patrick/src/e7/toolchain/stage2 --disable-shared
--disable-debug --disable-libssp --with-cpu=8540
Thread model: single
gcc version 4.9.1 (GCC)