[LLVMbugs] [Bug 17847] New: wrong code at -O2 and -O3 on x86_64-linux-gnu (affecting clang trunk, 3.3, and 3.2)

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=17847

            Bug ID: 17847
           Summary: wrong code at -O2 and -O3 on x86_64-linux-gnu
                    (affecting clang trunk, 3.3, and 3.2)
           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 by the current clang trunk and clang 3.3 at
-O2 and -O3 on x86_64-linux-gnu in both 32-bit and 64-bit modes. 

It also affects clang 3.2 and 2.9 at -O3 (not at -O2), but neither clang 3.0
nor 3.1. 

$ clang-trunk -v
clang version 3.4 (trunk 194255)
Target: x86_64-pc-linux-gnu
Thread model: posix
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
0
$ clang-trunk -O2 small.c; a.out
1
$ clang-trunk -O3 small.c; a.out
1
$ clang-3.3 -O2 small.c; a.out
1
$ clang-3.3 -O3 small.c; a.out
1
$ clang-3.2 -O2 small.c; a.out
0
$ clang-3.2 -O3 small.c; a.out
1
$
$ gcc-trunk -O2 small.c; a.out
0
$ 


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


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

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

int
fn1 (int p1, int p2)
{
  return p1 && p1 > 647 - p2 ? p1 : p1 + p2;
}

int
fn2 (char p1)
{
  int f = 0;
  for (; f < 36; f = fn1 (f, 8))
    {
      for (; c; c++);
      if (f ^ 1)
    {
      if (e)
        d = p1 ? 1 : 0;
      else if (p1)
        break;
      b = p1-- == 0;
    }
    }
  return f;
}

int
main ()
{
  g = fn2 (64);
  g || (a = 0);
  printf ("%d\n", a);
  return 0;
}

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