[LLVMbugs] [Bug 19138] New: wrong code (that segfaults) by LTO at all optimization levels (affecting 3.2 till trunk)

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=19138

            Bug ID: 19138
           Summary: wrong code (that segfaults) by LTO at all optimization
                    levels (affecting 3.2 till trunk)
           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 all
optimization levels (-O0 to -O3) on x86_64-linux-gnu (in both 32-bit and 64-bit
modes).  

It also affects clang 3.2, 3.3, and 3.4. 

$ clang-trunk -v
clang version 3.5.0 (trunk 203791)
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 small.c; a.out
$ 
$ clang-trunk -flto -O0 small.c
$ a.out
a.out: small.c:11: int main(): Assertion `b == &a' failed.
Aborted (core dumped)
$ 


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


#include <assert.h>

int a, *b, **volatile c = &b, *d = &a;

int
main ()
{
  for (a = 0; a < 1; a++)
    {
      *c = d;
      assert(b == &a);
    }
  return 0;
}

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