[LLVMbugs] [Bug 19889] New: wrong code by LTO at -O0 and -O1 on x86_64-linux-gnu (affecting 3.2 till trunk)

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=19889

            Bug ID: 19889
           Summary: wrong code by LTO at -O0 and -O1 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 -O0 and -O1 on x86_64-linux-gnu in both 32-bit and 64-bit modes. 


$ clang-trunk -v
clang version 3.5.0 (trunk 209780)
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 -Os small.c; a.out
$ 
$ clang-trunk -flto -O0 small.c
$ a.out
a.out: small.c:13: int main(): Assertion `b' failed.
Aborted (core dumped)
$ clang-3.4 -flto -O0 small.c
$ a.out
a.out: small.c:13: int main(): Assertion `b' failed.
Aborted (core dumped)
$ clang-3.3 -flto -O0 small.c
$ a.out
a.out: small.c:13: int main(): Assertion `b' failed.
Aborted (core dumped)
$ clang-3.2 -flto -O0 small.c
$ a.out
a.out: small.c:13: int main(): Assertion `b' failed.
Aborted (core dumped)
$ 


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


#include <assert.h>

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

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

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