[LLVMbugs] [Bug 19073] New: wrong code by LTO at -O0 on x86_64-linux-gnu in 64-bit mode

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=19073

            Bug ID: 19073
           Summary: wrong code by LTO at -O0 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 when using LTO at -O0 on
x86_64-linux-gnu in 64-bit mode (but not 32-bit mode). 

$ clang-trunk -v
clang version 3.5.0 (trunk 203119)
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 f.c main.c
$ a.out
1
$ clang-trunk -flto -m32 -O0 f.c main.c
$ a.out
1
$ clang-trunk -flto -m64 -O1 f.c main.c
$ a.out
1
$ 
$ clang-trunk -flto -m64 -O0 f.c main.c
$ a.out
0
$ 
$           
$ cat f.c 
extern int a, b, d, e, g;
extern long f;

static int
fn1 (int p)
{
  return b ? 0 : p;
}

int
fn2 ()
{
  int h = 1;
  e = d + 1;
  if (fn1 (e < 0))
    for (h = 0; h;)
      ;
  else
    {
      int i = 0, j = 0;
      g = a ? 0 : i;
      f = g;
      if (f || j || j || f >> j)
    ;
      for (d = 1; d; d = (char) d + 1)
    ;
    }
  return h;
}
$ cat main.c
extern int printf (const char *, ...);
extern int fn2 ();

int a, b, c, d, e, g, k;
long f;

int
main ()
{
  k = fn2 ();
  if (k)
    c = 1;
  printf ("%d\n", c);
  return 0;
}

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