[LLVMbugs] [Bug 18143] New: wrong code at -O3 on x86_64-linux-gnu (affecting trunk and 3.3)

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=18143

            Bug ID: 18143
           Summary: wrong code at -O3 on x86_64-linux-gnu (affecting trunk
                    and 3.3)
           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 clang 3.3 on
x86_64-linux-gnu at -O3 in both 32-bit and 64-bit modes.

This is a regression from clang 3.2. 

$ clang-trunk -v
clang version 3.5 (trunk 196455)
Target: x86_64-unknown-linux-gnu
Thread model: posix
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/4.6.3
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.6
$ 
$ clang-trunk -O2 small.c; a.out
1
$ clang-3.2 -O3 small.c; a.out
1
$ 
$ clang-trunk -O3 small.c; a.out
2
$ clang-3.3 -O3 small.c; a.out
2
$ 
$ gcc-trunk -O3 small.c; a.out
1
$ icc -O3 small.c; a.out
1
$ 


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


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

int a[2] = {0, 1}, b, c[1], *d = &c[0], e, f;

int
main ()
{
  int *g = &c[0];
  for (b = 0; b < 1; b++)
    {
      if (a[1])
    break;
      g = 0;
    }
  f = (&e == g) + 1;
  *d = f;
  printf ("%d\n", c[0]);
  return 0;
}

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