[LLVMbugs] [Bug 17906] New: wrong code at -O3 on x86_64-linux-gnu (affecting all clang versions)

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=17906

            Bug ID: 17906
           Summary: wrong code at -O3 on x86_64-linux-gnu (affecting all
                    clang versions)
           Product: clang
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: LLVM Codegen
          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
on x86_64-linux-gnu at -O3 in both 32-bit and 64-bit modes.

$ clang-trunk -v
clang version 3.4 (trunk 194528)
Target: x86_64-unknown-linux-gnu
Thread model: posix
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-trunk -O3 small.c; a.out
0
$ clang-3.3 -O3 small.c; a.out
0
$ clang-3.2 -O3 small.c; a.out
0
$ clang-3.1 -O3 small.c; a.out
0
$ clang-3.0 -O3 small.c; a.out
0
$ clang-2.9 -O3 small.c; a.out
0
$
$ gcc-trunk -O3 small.c; a.out
1
$ icc -O3 small.c; a.out
1
$ 
$ 


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


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

int *a, b, **e = &a, g;
long c;
char d;

int
fn1 (int p)
{
  return p;
}

static int
fn2 (int *p1, long *p2)
{
  char *f = &d;
  fn1 (*p2);
  *f = *p1;
  return 0;
}

void
fn3 ()
{
  fn2 (0, 0);
}

int
main ()
{
  for (b = 0; b < 1; b = 1)
    {
      *e = &g;
      *a = 1;
      fn2 (&g, &c);
    }
  printf ("%d\n", d);
  return 0;
}

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