[LLVMbugs] [Bug 18101] New: wrong code at -Os and above on x86_64-linux-gnu (affecting 3.1 till trunk)

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=18101

            Bug ID: 18101
           Summary: wrong code at -Os and above on x86_64-linux-gnu
                    (affecting 3.1 till 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 earlier
versions starting from 3.1) on x86_64-linux-gnu at -Os and above in both 32-bit
and 64-bit modes. 


$ clang-trunk -v
clang version 3.5 (trunk 195973)
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-3.0 -Os small.c; a.out
0
$ gcc-trunk -Os small.c; a.out
0
$ icc -Os small.c; a.out
0
$ 
$ clang-trunk -Os small.c; a.out
1
$ clang-3.3 -Os small.c; a.out
1
$ clang-3.2 -Os small.c; a.out
1
$ clang-3.1 -Os small.c; a.out
1
$           


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


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

struct S
{
  int f0;
  int f1:25; 
};

int a, b, *c = &b, d;

struct S
fn1 ()
{
  struct S e = {0, 0};
  if (!d)
    {
      struct S f = {0, -1};
      return f;
    }
  return e;
}

int
main ()
{
  struct S g = fn1 (), h = g;
  for (a = 0; a < 1; a++)
    {
      *c = 0;
      *c = 1 <= ((h.f0 >= *c) ^ (h.f1 |= 1));
    }
  printf ("%d\n", b);
  return 0;
}

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