[LLVMbugs] [Bug 21741] New: wrong code at -O2 and -O3 on x86_64-linux-gnu in 64-bit mode

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=21741

            Bug ID: 21741
           Summary: wrong code at -O2 and -O3 on x86_64-linux-gnu in
                    64-bit mode
           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 at -O2 and -O3 on
x86_64-linux-gnu in 64-bit mode (but not in 32-bit mode). 

This is a regression from 3.5.0. 

$ clang-trunk -v
clang version 3.6.0 (trunk 223263)
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 -m64 -Os small.c; a.out
$ clang-trunk -m32 -O2 small.c; a.out
$ clang-3.5.0 -m64 -O2 small.c; a.out
$ 
$ clang-trunk -m64 -O2 small.c
$ a.out
Segmentation fault (core dumped)
$ 


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


int a, b, c, d, e, h, k[4], l, n;
char f, m, g[3][5];

void
fn1 ()
{
  for (f = 2; f >= 0; f--)
    {
      k[f + d] = 0;
      for (h = 0; h < 2; h++)
    {
      for (; e < 2; e++)
        m = a;
      l = g[f][d + 1] & a & 1;
      n = k[0] >= 0 ? 1 : 1 >> b;
      if (n)
        break;
      for (c = 0; c < 1; c++)
        d = -5000000; 
    }
    }
}

int
main ()
{
  fn1 ();
  return 0;
}

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