[llvm-bugs] [Bug 28307] New: wrong code at -O3 on x86_64-linux-gnu (in both 32-bit and 64-bit modes)

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=28307

            Bug ID: 28307
           Summary: wrong code at -O3 on x86_64-linux-gnu (in both 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 clang trunk at -O3 on x86_64-linux-gnu
in both the 32-bit and 64-bit modes.

This is a regression from 3.8.x.  

It appears different from PR 28297. 


$ clang-trunk -v
clang version 3.9.0 (trunk 273774)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/local/bin
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/4.8.4
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
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
4
$ clang-3.8 -O3 small.c; ./a.out
4
$
$ clang-trunk -O3 small.c
$ ./a.out
0
$


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


int a, b, *c, e, f, g = 1, h, k, m, n, p;
static int **d = &c, j = 1;
short l = 1;

static void
fn1 (int p1)
{ 
  char t;
  int *r;
  unsigned s;
  if (g)
    { 
      int u, **v = &c;
      *d = &b;
      **d = h == p1;
      for (; p1 < 6; p1++)
        for (t = 0; t < 5; t += 4)
          { 
            m = 0;
            if (**v ? ~0 % **v : ~0)
              { 
                if (l)
                  *v = &p;
              }
            else
              return;
            u = 0;
            for (; u < 1; u++)
              r = &b;
            *v = r;
            s = j ? j : a;
            if (**v % s & 10)
              return;
          }
      *c = 4;
    }
  n = b;
  f = 0;
}

void
fn2 ()
{ 
  fn1 (1);
  while (k)
    e++;
  j = 0;
}

int
main ()
{ 
  fn2 ();
  __builtin_printf ("%d\n", b);
  return 0;
}

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