[LLVMbugs] [Bug 19146] New: wrong code by LTO at -O3 on x86_64-linux-gnu (affecting 3.4 and trunk)

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=19146

            Bug ID: 19146
           Summary: wrong code by LTO at -O3 on x86_64-linux-gnu
                    (affecting 3.4 and trunk)
           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 and 3.4 miscompile the following code when using LTO at
-O3 on x86_64-linux-gnu (in both 32-bit and 64-bit modes). 

This is regression from 3.3. 

$ clang-trunk -v
clang version 3.5.0 (trunk 203921)
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 -O3 small.c; a.out
-1
$ clang-trunk -flto -O2 small.c; a.out
-1
$ clang-3.3 -flto -O3 small.c; a.out
-1
$ 
$ clang-trunk -flto -O3 small.c; a.out
0
$ clang-3.4 -flto -O3 small.c; a.out
0
$ 


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


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

int j, k, l, m[2], v, a;

int
main ()
{
  int s = m[0] = j = 0;

  for (; j >= 0; --j)
    {
      a = k >= 0 || s ? 0 : k;
      l = a >= 0;
      if (m[1])
    break;
      s = l;
    }

  k = printf ("%d\n", j);

  for (; v < 1; v++)
    m[v] = 0;

  return 0;
}

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