[LLVMbugs] [Bug 19078] New: wrong code by LTO at -O0 and -O1 on x86_64-linux-gnu (both 32-bit and 64-bit modes)

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=19078

            Bug ID: 19078
           Summary: wrong code by LTO at -O0 and -O1 on x86_64-linux-gnu
                    (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: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

The current clang trunk miscompiles the following code when using LTO at -O0
and -O1 (but not at -Os and above) on x86_64-linux-gnu (in both 32-bit and
64-bit modes). 

$ clang-trunk -v
clang version 3.5.0 (trunk 203239)
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 -O0 small.c; a.out
-1
$ clang-trunk -flto -Os small.c; a.out
-1
$             
$ clang-trunk -flto -O0 small.c; a.out
0
$ clang-trunk -flto -O1 small.c; a.out
0
$ 


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


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

int a, b, c, d = 1, e, g, h;
short f;

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

int
fn2 ()
{
  return b = 0;
}

void
fn3 (int p)
{
  int i, j = d = 0;
  i = 1 ? 1 : 0;
  f = j || j || 0 > j ? 0 : j;
  if (!(1 & i && f))
    {
      if (g)
    ;
      for (g = 0; g != 1; g++)
    {
      g || fn1 (fn2 (), p);
      if (!d)
        {
          e = g || a;
          break;
        }
    }
      for (h = -1; c >= 0; c = h)
    if (g)
      break;
    }
}

int
main ()
{
  fn3 (1);
  printf ("%d\n", c);
  return 0;
}

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