[LLVMbugs] [Bug 19907] New: wrong code by LTO at -Os and above on x86_64-linux-gnu

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=19907

            Bug ID: 19907
           Summary: wrong code by LTO at -Os and above on x86_64-linux-gnu
           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 miscompiles the following code when using LTO at -Os
and above on x86_64-linux-gnu (in both 32-bit and 64-bit modes). 

This is a regression from 3.4. 

$ clang-trunk -v
clang version 3.5.0 (trunk 209947)
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
$ clang-3.4 -flto -Os small.c; a.out
$ 
$ clang-trunk -flto -Os small.c; a.out
Aborted (core dumped)
$ 


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


int a, b, c, d = 1, e, f = 1;

void
fn1 ()
{
  a = 1;
}

int
main ()
{
  fn1 ();

lbl:
  e || (b = 0);
  if (f)
    d = 0;
  if (a)
    {
      c = a;
      f = 0;
      a = 0;
      goto lbl;
    }

  if (c != 1)
    __builtin_abort ();

  return 0;
}

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