[LLVMbugs] [Bug 19109] New: wrong code (that segfaults) by LTO at -O2 and -O3 on x86_64-linux-gnu

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=19109

            Bug ID: 19109
           Summary: wrong code (that segfaults) by LTO at -O2 and -O3 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 -O2
and -O3 on x86_64-linux-gnu (in both 32-bit and 64-bit modes). 

This is likely related to http://llvm.org/bugs/show_bug.cgi?id=19062. 

$ clang-trunk -v
clang version 3.5.0 (trunk 203564)
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
$ clang-trunk -flto -Os small.c; a.out
$      
$ clang-trunk -flto -O2 small.c  
$ a.out
a.out: small.c:13: void foo(): Assertion `a == 0' failed.
Aborted (core dumped)
$ 


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


#include <assert.h>

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

void
foo ()
{
  for (;;)
    {
      assert (a == 0);
      *f = &g;
      *b = 0;
      assert (a == 0);
      *f = 0;
      if (*e)
    break;
    }
}

int
main ()
{
  *d = 1;
  assert (a == 0);
  foo ();
  return 0;
}

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