[LLVMbugs] [Bug 19885] New: wrong code by LTO at -Os (only) on x86_64-linux-gnu (affecting 3.2 till trunk)

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=19885

            Bug ID: 19885
           Summary: wrong code by LTO at -Os (only) on x86_64-linux-gnu
                    (affecting 3.2 till trunk)
           Product: clang
           Version: unspecified
          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 (also 3.2 till 3.4) miscompiles the following code when
using LTO at -Os on x86_64-linux-gnu in both 32-bit and 64-bit modes. 


$ clang-trunk -v
clang version 3.5.0 (trunk 209730)
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
0
$ clang-trunk -flto -O1 small.c; a.out
0
$ clang-trunk -flto -O2 small.c; a.out
0
$           
$ clang-trunk -flto -Os small.c; a.out
1
$ clang-3.4 -flto -Os small.c; a.out
1
$ clang-3.3 -flto -Os small.c; a.out
1
$ clang-3.2 -flto -Os small.c; a.out
1
$ 


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


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

int a = 1, c, *f = &c, g, *h, *i = &a, *k = &c, l;  
char b, *d = &b, **e = &d, ***j = &e;

static int
fn1 ()
{
  int m;
  l = **e;
  *f = 1;
  for (m = 0; m < 2; m++)
    **e = (*k || (h = &g) == (int *)&f) == 0;
  for (; b >= 0; b--)
    ;
  if (**e)
    *i = 0;
  return 0;
}

int
main ()
{
  fn1 ();
  printf ("%d\n", a);
  return 0;
}

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