[llvm-bugs] [Bug 27262] New: wrong code at -O3 on x86_64-linux-gnu in 32-bit and 64-bit modes

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=27262

            Bug ID: 27262
           Summary: wrong code at -O3 on x86_64-linux-gnu in 32-bit and
                    64-bit modes
           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: llvm-bugs at lists.llvm.org
    Classification: Unclassified

The following code is miscompiled by the current clang trunk on
x86_64-linux-gnu at -O3 in both the 32-bit and 64-bit modes.  

This is a regression from 3.8.x. 

This one has been very tough to reduce. 


$ clang-trunk -v
clang version 3.9.0 (trunk 265520)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/local/tools/bin
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/4.9
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/4.9.3
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/5.3.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4.7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.6
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.6.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.7.3
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8.5
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9.3
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5.3.0
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Candidate multilib: x32;@mx32
Selected multilib: .;@m64
$ 
$ clang-trunk -O2 small.c; ./a.out
0
$ clang-3.8 -O3 small.c; ./a.out
0
$ 
$ clang-trunk -O3 small.c; ./a.out
3
$ 


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



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

int a[6], e, k, p, r;
unsigned c;
short d, f, l, q;
long g, h;
char j, m, n, o;

void
fn1 (int p1)
{
  c = c >> 8 ^ a[c ^ (p1 & 5)];
}

void
fn2 (long long p1)
{
  int b = p1;
  c = c >> 8 ^ a[c ^ (b & 5)] >> 8 ^ a[(c ^ 5) & 5];
  c = c >> 8 ^ a[(c ^ 5) & 5];
  fn1 (p1 >> 4);
  fn1 (p1 >> 2);
  fn1 (p1 >> 40);
  c = c >> 8 ^ a[(c ^ 6) & 5];
}

void
fn3 (long long p1, int p3)
{
  fn2 (p1);
  if (p3)
    printf ("%d\n", 5);
}

static void
fn4 ()
{
  int s, i = 0, u = 1;
  char t[3];
 lbl: 
  for (; i < 3; i++)
    t[i] = 1;
  int v;
  i = 0;
  for (; u < 20; ++u)
    {
      if (m)
    goto lbl; 
      if (j)
    {
      s = 0;
      for (; s < 9; s++)
        fn3 (g, v);
    }
      h = 0;
      for (; h < 3; h++)
    {
      o ^= k &= d-- + (n && f == (n = l));
      e = 0;
      for (; e < 3; e++)
        {
          if (t[h])
        break;
          p = q;
        }
    }
    }
  v = r;
}

int
main ()
{
  fn4 ();
  printf ("%d\n", e);
  return 0; 
}

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