[LLVMbugs] [Bug 19670] New: wrong code at -O2 on x86_64-linux-gnu (affecting trunk and 3.4)

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=19670

            Bug ID: 19670
           Summary: wrong code at -O2 on x86_64-linux-gnu (affecting trunk
                    and 3.4)
           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: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

The following code is miscompiled by the current clang trunk and clang 3.4 on
x86_64-linux-gnu at -O3 (in both 32-bit and 64-bit modes). The generated code
hangs. 

This is a regression from 3.3. 

$ clang-trunk -v
clang version 3.5.0 (trunk 208085)
Target: x86_64-unknown-linux-gnu
Thread model: posix
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/4.8
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/4.8.1
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/4.6.4
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/4.8.1
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Selected multilib: .;@m64
$ 
$ clang-trunk -Os small.c; a.out
$ clang-3.3 -O2 small.c; a.out
$ 
$ clang-trunk -O2 small.c
$ a.out        
^C
$ clang-3.4 -O2 small.c
$ a.out
^C
$ 

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

int a, b, d, e, f, g, h, i, k, l, m, n;
short c;

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

void
fn4 (int p)
{
  for (; p; p++)
    if (c)
      for (; d;)
    f = 0;
}

static unsigned int
fn3 (short p)
{
  if (k)
    for (; g;)
      if (e)
    l = p;
  if (p)
    for (; m; ++m)
      if (c)
    for (; d;)
      ;
  n = b ? 0 : a;
  fn4 (p ^ (n > 0));
  return c;
}

static char
fn2 ()
{
  int j = -9;
  for (; j; j = fn1 (j, 0))
    {
      for (; i;)
    fn3 (j);
      if (j)
    for (; e;)
      ;
    }
  return 0;
}

int
fn5 ()
{
  fn2 ();
  for (h = 0; h; h = fn3 (0))
    ;
  return 0;
}

int
main ()
{
  fn5 ();
  return 0;
}

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