[LLVMbugs] [Bug 17969] New: wrong code at -Os and above on x86_64-linux-gnu (affecting trunk, and 3.3 but only at -O3)

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=17969

            Bug ID: 17969
           Summary: wrong code at -Os and above on x86_64-linux-gnu
                    (affecting trunk, and 3.3 but only at -O3)
           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 on
x86_64-linux-gnu at -Os and above in both 32-bit and 64-bit modes. 

It is also miscompiled by clang 3.3, but only at -O3. 

The bug goes away with -fno-vectorize, so it should be a bug in the vectorizer.

$ clang-trunk -v
clang version 3.4 (trunk 194963)
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 -O1 small.c; a.out
1
$ clang-trunk -Os small.c; a.out
0
$ clang-3.3 -Os small.c; a.out
1
$ clang-3.3 -O3 small.c; a.out
0
$ clang-3.2 -Os small.c; a.out
1
$ clang-3.2 -O2 small.c; a.out
1
$ clang-3.2 -O3 small.c; a.out
1
$ 
$ clang-trunk -Os -fno-vectorize small.c; a.out
1
$  


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


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

int a, *b = &a;

int
main ()
{
  short c = 0;
 lbl:
  ++c;
  *b |= 1;
  if (c)
    goto lbl;
  printf ("%d\n", a);
  return 0;
}

-- 
You are receiving this mail because:
You are on the CC list for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-bugs/attachments/20131117/5c95e014/attachment.html>