[LLVMbugs] [Bug 17794] New: wrong code at -O2 on x86_64-linux-gnu

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=17794

            Bug ID: 17794
           Summary: wrong code at -O2 on x86_64-linux-gnu
           Product: clang
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: LLVM Codegen
          Assignee: unassignedclangbugs at nondot.org
          Reporter: su at cs.ucdavis.edu
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

The following code is miscompiled (the generated code hangs) by the current
clang trunk on x86_64-linux-gnu at -O2 in both 32-bit and 64-bit modes. 

This is a regression from clang 3.3. 

$ clang-trunk -v
clang version 3.4 (trunk 193964)
Target: x86_64-pc-linux-gnu
Thread model: posix
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4.6
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/4.6.3
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.6
$ 
$ clang-trunk -Os small.c; a.out
$ clang-3.3 -O2 small.c; a.out
$ 
$ clang-trunk -O2 small.c
$ a.out
^C
$ 
$ gcc-trunk -O2 small.c; a.out
$ icc -O2 small.c; a.out
$ 


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


int a, b, c, d, f;
char e;

int
fn1 (int p1, int p2)
{
  return p1 > 0 || 1 < -p2 ? p1 : p1 + 1;
}

int
fn2 (unsigned short p1, unsigned short p2)
{
  return p1 - p2;
}

void
fn3 (int p1, int p2)
{
  for (; p1 < 13; ++p1)
    {
      e = p1 * 2;
      if (e < a && a)
    if (p2 ^ b)
      c = 0;
    }
}

static int
fn4 (short p)
{
  for (d = 1; d;)
    {
      int h = -7;
      h = fn2 (p, h);
      if (h)
    return 0;
      fn3 (0, p);
    }
  fn3 (0, 0);
  return 0;
}

static int
fn5 ()
{
  int g = -19;
  for (; g; g = fn1 (g, 0))
    {
      for (; f; f++)
    fn4 (g);
      if (g)
    b = 0;
    }
  return 0;
}

static int
fn6 ()
{
  fn5 ();
  fn4 (0);
  return 0;
}

int
main ()
{
  fn6 ();
  return 0;
}

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