[LLVMbugs] [Bug 23309] New: wrong code at -O1 and above on x86_64-linux-gnu

[bugzilla-daemon at llvm.org]

https://llvm.org/bugs/show_bug.cgi?id=23309

            Bug ID: 23309
           Summary: wrong code at -O1 and above 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 following code is miscompiled by the current clang trunk (and 3.6.0) on
x86_64-linux-gnu at -O1 and above in both 32-bit and 64-bit modes.

This is a regression from 3.5.0.


$ clang-trunk -v
clang version 3.7.0 (trunk 235404)
Target: x86_64-unknown-linux-gnu
Thread model: posix
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/4.9
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/4.9.2
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/5.0.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4.7
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/4.8.2
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9.2
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5.0.0
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Candidate multilib: x32;@mx32
Selected multilib: .;@m64
$ 
$ clang-trunk -O0 small.c; ./a.out
$ clang-3.5.0 -O1 small.c; ./a.out
$ 
$ clang-trunk -O1 small.c
$ ./a.out
Aborted (core dumped)
$ 
$ clang-3.6.0 -O1 small.c
$ ./a.out
Aborted (core dumped)
$ 


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


int a, b, c, e, f;

int
fn1 ()
{
  int g;
  char i;
  for (; b < 1; b++)
    {
      c = 0;
      e = f || a + 1;
      i = 1 - c;
      g = -3 - i - e;
      if (g & 1)
    return 0;
    }
  return 0;
}

int
main ()
{
  fn1 ();

  if (b)
    __builtin_abort ();

  return 0;
}

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