[LLVMbugs] [Bug 18984] New: wrong code by LTO at -O0 on x86_64-linux-gnu

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=18984

            Bug ID: 18984
           Summary: wrong code by LTO at -O0 on x86_64-linux-gnu
           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 on
x86_64-linux-gnu (in both 32-bit and 64-bit modes). 

$ clang-trunk -v
clang version 3.5 (trunk 202330)
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
$ clang-trunk -flto -O1 small.c; a.out
$     
$ clang-trunk -flto -O0 small.c; a.out
Aborted (core dumped)
$ 


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


int a, b, d, *e = &d; 
int volatile c = 1;

void
foo (int *p)
{
  int f = 0;
  for (; b < 1; b++)
    {
      e = p;
      if (c)
    {
      if (f)
        ;
      break;
    }
      if (c)
    break;
    }
  if (!e) 
    __builtin_abort(); 
}

int
main ()
{
  foo (&a);
  return 0;
}

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