[llvm-bugs] [Bug 28297] New: wrong code at -O3 on x86_64-linux-gnu (in both 32-bit and 64-bit modes)

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=28297

            Bug ID: 28297
           Summary: wrong code at -O3 on x86_64-linux-gnu (in both 32-bit
                    and 64-bit modes)
           Product: clang
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: su at cs.ucdavis.edu
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

The following code is miscompiled by the clang trunk at -O3 on x86_64-linux-gnu
in both the 32-bit and 64-bit modes.

This is a regression from 3.8.x. 


$ clang -v
clang version 3.9.0 (trunk 273554)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/local/clang-trunk/bin
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/4.9
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/4.9.3
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/5
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/5.3.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4.7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.6
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.6.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.7.3
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8.5
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9.3
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5.3.0
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Candidate multilib: x32;@mx32
Selected multilib: .;@m64
$ 
$ clang -O2 small.c; ./a.out
0
$ clang-3.8 -O3 small.c; ./a.out
0
$ 
$ clang -O3 small.c
$ ./a.out
0
Aborted (core dumped)
$ 


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


int a, *b = &a, c, d, e = 1, f = 1, g, h, i, j, k, l;

static void fn1 ()
{
  unsigned p;
  int q;
  __builtin_printf ("0\n");
  q = e;
  for (d = 0; d < 4; d += 2)
    {
      p = q && b;
      q |= p;
      if (h)
    {
      for (g = 1; g; g = 0)
        for (; i; i++)
          {
        c = j;
        if (l)
          k = 4;
          }
      return;
    }
      if ((f || k < f) && (q > 6))
    {
      j = 1;
      return;
    }
    }
}

int main ()
{
  for (;;)
    {
      fn1 ();
      if (e)
    break;
    }

  if (c != 0) 
    __builtin_abort (); 

  return 0;
}

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