[Bug tree-optimization/64853] New: wrong code at -Os and above on x86_64-linux-gnu

[su at cs dot ucdavis.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64853

            Bug ID: 64853
           Summary: wrong code at -Os and above on x86_64-linux-gnu
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu

The current gcc trunk miscompiles the following code on x86_64-linux at -Os and
above 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 20150128 (experimental) [trunk revision 220198] (GCC) 
$ 
$ gcc-trunk -O1 small.c; ./a.out
$ gcc-4.9 -Os small.c; ./a.out
$ 
$ gcc-trunk -Os small.c
$ ./a.out
Aborted (core dumped)
$ 



---------------------------------



struct S
{
  int f1;
};

static struct S a = { 1 };
char b;
static unsigned char *c = &b;
int d, e, f;

int
fn1 (int p)
{
  return 0 ? 0 : p - 1;
}

static int
fn2 (struct S p)
{
  int g = 200;
  for (e = 4; e; e = fn1 (e))
    {
      for (; d; d++)
    ;
      *c &= p.f1 & g;
      g = --*c;
      if (f)
    return 0;
    }
  return 0;
}

int
main ()
{
  fn2 (a);

  if (b != 0) 
    __builtin_abort (); 

  return 0;
}