[LLVMbugs] [Bug 19093] New: wrong code by LTO at -Os and above 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=19093

            Bug ID: 19093
           Summary: wrong code by LTO at -Os and above 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 -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 203396)
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 -Os small.c; a.out
1
$ clang-trunk -flto -O1 small.c; a.out
1
$ 
$ clang-trunk -flto -Os small.c; a.out
0
$ 


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


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

int a[2], b = 2, c, *d = &c, **e = &d, ***f = &e, *g = &b, *h = &b, i;

static int
fn1 ()
{
  for (c = 2; c; c--)
    for (;;)
      {
    *g &= **e;
    for (; i; i++)
      ;
    if (*h)
      break;
    return 0;
      }
  return 0; 
}

int
main ()
{
  a[1] = 1;
  fn1 ();
  printf ("%d\n", a[c]);
  return 0;
}

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