[LLVMbugs] [Bug 17504] New: wrong code at -Os in 64-bit mode (affecting all clang versions on x86_64-linux-gnu and MacOS X)

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=17504

            Bug ID: 17504
           Summary: wrong code at -Os in 64-bit mode (affecting all clang
                    versions on x86_64-linux-gnu and MacOS X)
           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 -Os in 64-bit mode (but not 32-bit mode). 

It also affects MacOS X. 

I had hoped to reduce the testcase further, but it's the best I've been able to
get so far. 


$ clang-trunk -v
clang version 3.4 (trunk 192089)
Target: x86_64-pc-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
-46
$ clang-trunk -O2 small.c; a.out
-46
$ clang-trunk -Os small.c; a.out
-44
$ clang-3.3 -Os small.c; a.out
-44
$ clang-3.2 -Os small.c; a.out
-44
$ clang-3.1 -Os small.c; a.out
-44
$ clang-3.0 -Os small.c; a.out
-44
$ gcc-trunk -Os small.c; a.out
-46
$ 



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


int printf (const char *, ...);
struct S
{
  int f0;
  int f3;
  int f6;
  int f7;
  int f8;
};

int a;
static struct S b;

char
fn1 (char p1, char p2)
{
  return p1 + p2;
}

void
fn3 (struct S p1)
{
}

int
fn4 ()
{
  a--;
  return 0;
}

static int
fn2 ()
{
  char c = 117;
  b.f0 = 0;
  for (; b.f0 < 44; b.f0 = fn1 (b.f0, 4))
    {
      fn3 (b);
      a--;
      c++;
      c && fn4 ();
    }
  a--;
  return 0;
}

int
main ()
{
  a = b.f3;
  fn2 ();
  fn2 ();
  printf ("%d\n", a);
  return 0;
}

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