[llvm-bugs] [Bug 27261] New: wrong code at -O3 on x86_64-linux-gnu

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=27261

            Bug ID: 27261
           Summary: wrong code at -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: llvm-bugs at lists.llvm.org
    Classification: Unclassified

The following code is miscompiled by the current clang trunk on
x86_64-linux-gnu at -O3 in both the 32-bit and 64-bit modes.  

This is a regression from 3.8.x. 


$ clang-trunk -v
clang version 3.9.0 (trunk 265520)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/local/clang-trunk/bin
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/4.9
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/4.9.3
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/5.3.0
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/4.8.5
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9.3
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5.3.0
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-3.8 -O3 small.c; ./a.out
2
$ clang-trunk -O2 small.c; ./a.out
2
$ 
$ clang-trunk -O3 small.c; ./a.out
0
$ 


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



int printf (const char *, ...);

int a, b, c, d;
char e;

void
fn1 (int p1)
{
  for (a = 1; a >= 0; a--)
    {
      e = p1;
      for (;;)
    {
      for (c = 0; c < 1; c++)
        {
          d = a ? d / a : d; 
          for (; e < 2; e++)
        p1 = 1; 
          if (p1)
        break;
          b = 1;
        }
      if (p1 >= 0)
        break;
      for (;;)
        ;
    }
    }
}

int
main ()
{
  fn1 (0);
  printf ("%d\n", e);
  return 0; 
}

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