https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64684
Bug ID: 64684
Summary: wrong code by LTO on x86_64-linux-gnu
Product: gcc
Version: 5.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: lto
Assignee: unassigned at gcc dot gnu.org
Reporter: su at cs dot ucdavis.edu
The current gcc trunk miscompiles the following code when using LTO on
x86_64-linux-gnu in both 32-bit and 64-bit modes.
This is a regression from 4.9.x.
$ gcc-trunk -v
Using built-in specs.
COLLECT_GCC=gcc-trunk
COLLECT_LTO_WRAPPER=/usr/local/gcc-trunk/libexec/gcc/x86_64-unknown-linux-gnu/5.0.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../gcc-trunk/configure --prefix=/usr/local/gcc-trunk
--enable-languages=c,c++ --disable-werror --enable-multilib
Thread model: posix
gcc version 5.0.0 20150119 (experimental) [trunk revision 219832] (GCC)
$
$ gcc-trunk -O1 -c fn1.c
$ gcc-trunk -Os -c fn2.c
$ gcc-trunk -O0 -c main.c
$ gcc-trunk -O0 fn1.o fn2.o main.o
$ ./a.out
$
$
$ gcc-4.9 -flto -O1 -c fn1.c
$ gcc-4.9 -flto -Os -c fn2.c
$ gcc-4.9 -flto -O0 -c main.c
$ gcc-4.9 -flto fn1.o fn2.o main.o
$ ./a.out
$
$ gcc-trunk -flto -O1 -c fn1.c
$ gcc-trunk -flto -Os -c fn2.c
$ gcc-trunk -flto -O0 -c main.c
$ gcc-trunk -flto fn1.o fn2.o main.o
$ ./a.out
Aborted (core dumped)
$
$ cat fn1.c
extern void fn2 (void);
extern int a;
void
fn1 ()
{
a = -1;
fn2 ();
a &= 1;
}
$ cat fn2.c
extern int a;
void
fn2 (void)
{
a = 0;
}
$ cat main.c
extern void fn1 (void);
int a;
int
main ()
{
fn1 ();
if (a != 0)
__builtin_abort ();
return 0;
}
$
