[LLVMbugs] [Bug 18000] New: wrong code at -Os and above on x86_64-linux-gnu

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=18000

            Bug ID: 18000
           Summary: wrong code at -Os and above 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 following code is miscompiled by the current clang trunk and clang 3.3 at
-Os and above on x86_64-linux-gnu in both 32-bit and 64-bit modes. 

It also affects clang 3.2 at -Os (but neither -O2 nor -O3). 

This is a regression from clang 3.1. 

$ clang-trunk -v
clang version 3.4 (trunk 195148)
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
0
$ clang-3.1 -Os small.c; a.out
0
$
$ clang-trunk -Os small.c; a.out
512
$ clang-3.3 -Os small.c; a.out
512
$ clang-3.2 -Os small.c; a.out
512
$ 


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


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

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

void
foo ()
{
  a = 0;
}

int
main ()
{
  unsigned char f;
  for (; b < 1; b++)
    for (e = 1; e >= 0; e--)
      {
    d = 0;
    if (a)
      break;
    f = 179 * e;
    c = f << 1;
    foo ();
      }
  printf ("%d\n", c);
  return 0;
}

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