[LLVMbugs] [Bug 18223] New: wrong code at -O3 on x86_64-linux-gnu (affecting clang 3.0 till the trunk)

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=18223

            Bug ID: 18223
           Summary: wrong code at -O3 on x86_64-linux-gnu (affecting clang
                    3.0 till the trunk)
           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 older
versions from 3.0) on x86_64-linux-gnu at -O3 in both 32-bit and 64-bit modes.

It also seems to affect MacOS X. 

This is a regression from 2.9. 

$ clang-trunk -v
clang version 3.5 (trunk 197135)
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
0
$ clang-trunk -O3 small.c; a.out
1
$ 


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


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

int b, c, d, f, h;

int
main ()
{
  for (b = 0; b < 5; b++)
    {
      f = b - (unsigned int) (d = 1) >= b; 
      if (c)
    h = 0;
    }
  printf ("%d\n", f);
  return 0;
}

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