[LLVMbugs] [Bug 22222] New: wrong code at -O2 and -O3 on x86_64-linux-gnu

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Tue Jan 13 22:58:41 PST 2015


http://llvm.org/bugs/show_bug.cgi?id=22222

            Bug ID: 22222
           Summary: wrong code at -O2 and -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: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

The current clang trunk miscompiles the following code at -O2 and -O3 on
x86_64-linux-gnu in both 32-bit and 64-bit modes.

This is a regression from 3.5.0. 

$ clang-trunk -v
clang version 3.6.0 (trunk 225679)
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-3.5.0 -O2 small.c; a.out
$ 
$ clang-trunk -O2 small.c
$ a.out
Aborted (core dumped)
$ 


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


int a, b, c;

int
main ()
{
  int d = 1;
  for (b = 0; b < 1; b++)
    {
      for (c = 0; c < 1; c++)
        a |= -d + c;
      d = 0;
    }

  if (a != -1)
    __builtin_abort ();

  return 0;
}

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