[Bug rtl-optimization/64756] New: wrong code at -O3 on x86_64-linux-gnu (in 32-bit mode)

[su at cs dot ucdavis.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64756

            Bug ID: 64756
           Summary: wrong code at -O3 on x86_64-linux-gnu (in 32-bit mode)
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-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 -O3 in
the 32-bit mode (but not in 64-bit mode). 

This is a regression from 4.9.x. 

It is quite strange that the bug seems to be sensitive to the name of the
variable "tmp" --- changing the variable to "b" for example will mask it. 

$ 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 20150122 (experimental) [trunk revision 220011] (GCC) 

$ 
$ gcc-trunk -m32 -O2 small.c; a.out
$ gcc-trunk -m64 -O3 small.c; a.out
$ gcc-4.9 -m32 -O3 small.c; a.out
$ 
$ gcc-trunk -m32 -O3 small.c 
$ ./a.out
Aborted (core dumped)
$ 


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



int a, *tmp, **c = &tmp;
volatile int d;
static int *volatile *e = &tmp;
unsigned int f; 

static void
fn1 (int *p)
{
  int g;
  for (; f < 1; f++)
    for (g = 1; g >= 0; g--)
      {
    d || d;
    *c = p;

    if (tmp != &a)
      __builtin_abort (); 

    *e = 0;
      }
}

int
main ()
{
  fn1 (&a);
  return 0;
}