gcc -O2 -flto 1.c 2.c hangs. -O1 or without -flto compiles and links just fine.
1.c: struct bar {int x;}; extern struct bar foo(void); int main() { struct bar x=foo(); return 0; } 2.c: typedef struct{int x;} bar; bar foo (void) { bar x; return x; } gcc -v: Using built-in specs. COLLECT_GCC=/usr/x86_64-pc-linux-gnu/gcc-bin/4.5.0-alpha20100318/gcc COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-pc-linux-gnu/4.5.0-alpha20100318/lto-wrapper Target: x86_64-pc-linux-gnu Configured with: /var/tmp/portage/sys-devel/gcc-4.5.0_alpha20100318/work/gcc-4.5-20100318/configure --prefix=/usr --bindir=/usr/x86_64-pc-linux-gnu/gcc-bin/4.5.0-alpha20100318 --includedir=/usr/lib/gcc/x86_64-pc-linux-gnu/4.5.0-alpha20100318/include --datadir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.5.0-alpha20100318 --mandir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.5.0-alpha20100318/man --infodir=/usr/share/gcc-data/x86_64-pc-linux-gnu/4.5.0-alpha20100318/info --with-gxx-include-dir=/usr/lib/gcc/x86_64-pc-linux-gnu/4.5.0-alpha20100318/include/g++-v4 --host=x86_64-pc-linux-gnu --build=x86_64-pc-linux-gnu --disable-altivec --disable-fixed-point --with-ppl --with-cloog --enable-nls --without-included-gettext --with-system-zlib --disable-checking --disable-werror --enable-secureplt --enable-multilib --enable-libmudflap --disable-libssp --enable-libgomp --enable-cld --with-python-dir=/share/gcc-data/x86_64-pc-linux-gnu/4.5.0-alpha20100318/python --disable-libgcj --enable-languages=c,c++ --enable-shared --enable-threads=posix --enable-__cxa_atexit --enable-clocale=gnu --with-bugurl=http://bugs.gentoo.org/ --with-pkgversion='Gentoo 4.5.0_alpha20100318' --enable-lto Thread model: posix gcc version 4.5.0-alpha20100318 20100318 (experimental) (Gentoo 4.5.0_alpha20100318) -- Summary: Compiler hang with -O2 -flto Product: gcc Version: 4.5.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: lto AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: marbacz at gmail dot com http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43455