[Bug rtl-optimization/68328] New: wrong code at -O2 and -O3 on x86_64-linux-gnu

[su at cs dot ucdavis.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68328

            Bug ID: 68328
           Summary: wrong code at -O2 and -O3 on x86_64-linux-gnu
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu
  Target Milestone: ---

The current gcc trunk mis-compiles the following code on x86_64-linux-gnu at
-O2 and -O3 in the 64-bit mode (but not in the 32-bit mode). 

It also affects 4.9.x and later releases, making it a regression from 4.8.x. 

$ gcc-trunk -v
Using built-in specs.
COLLECT_GCC=gcc-trunk
COLLECT_LTO_WRAPPER=/usr/local/gcc-trunk/libexec/gcc/x86_64-pc-linux-gnu/6.0.0/lto-wrapper
Target: x86_64-pc-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 6.0.0 20151112 (experimental) [trunk revision 230270] (GCC) 
$ 
$ gcc-trunk -Os small.c; ./a.out
$ gcc-4.8 -O2 small.c; ./a.out
$ 
$ gcc-trunk -O2 small.c
$ ./a.out
0
$ 


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


int printf (const char *, ...); 

int a, b, c = 1, d = 1, e;

int
fn1 (int p1)
{
  char g, h;
  int i, j;

  for (;;)
    {
      if (c)
        h = d;
      g = h < p1 ? h : 0; 
      i = (char) ((g - 120) ^ 1);
      j = i > 97;
      if (a - j)
        printf ("%d\n", 0);
      if (!b)
        return e;
    }
}

int
main ()
{
  fn1 (2);
  return 0;
}