[LLVMbugs] [Bug 19219] New: wrong code by LTO at -O2 and -O3 on x86_64-linux-gnu (affecting all clang versions)

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=19219

            Bug ID: 19219
           Summary: wrong code by LTO at -O2 and -O3 on x86_64-linux-gnu
                    (affecting all clang versions)
           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 -O2
and -O3 on x86_64-linux-gnu in both 32-bit and 64-bit modes. 

This also affects earlier clang versions (e.g. 3.2, 3.3, and 3.4). 

$ clang-trunk -v
clang version 3.5.0 (trunk 204339)
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 -O2 small.c; a.out
1
$ clang-trunk -flto -Os small.c; a.out
1
$
$ clang-trunk -flto -O2 small.c; a.out
0
$ clang-3.4 -flto -O2 small.c; a.out
0
$ clang-3.3 -flto -O2 small.c; a.out
0
$ clang-3.2 -flto -O2 small.c; a.out
0
$


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


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

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

int
main ()
{ 
  char *n[9];
  for (j = 0; j < 9; j++)
    n[j] = &a;
  for (h = 1; h; h--)
    { 
      *l = 0;
      f = &m;
      c = *n[0];
      **e = 1;
      k = ***g;
      *f = k && c;
    }
  i;
  printf ("%d\n", b);
  return 0;
}

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