[llvm-bugs] [Bug 24799] New: wrong code at -O3 on x86_64-linux-gnu

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=24799

            Bug ID: 24799
           Summary: wrong code at -O3 on x86_64-linux-gnu
           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 32-bit and 64-bit modes.

This is a regression from 3.7.x.


$ clang-trunk -v
clang version 3.8.0 (trunk 247514)
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/4.9.2
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/5.1.0
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/4.8.2
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.9.2
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/5.1.0
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
$ clang-3.7.0 -O3 small.c; ./a.out
$ 
$ clang-trunk -O3 small.c
$ ./a.out
Aborted
$ 


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


int a[6], b, e, f, g, h, i = 1, j, k, l, m;

struct
{
  char f0;
} c[6], d;

static int
fn1 (int p1)
{
  for (m = 0; m < 6; m++)
    for (g = 0; g < 6; g++)
      {
    for (; k; k++)
      ;
    if (f)
      b &= 1 ^ a[b & 1];
    if (l)
      for (;;)
        ;
    d = c[m] = c[g];
    for (h = 0; h < 1; h++)
      {
        int n[0];
        for (;; e++)
          {
        if (p1)
          break;
        p1 = 1 | n[0];
          }
      }
    j = c[1].f0 = 1;
      }
  return 0;
}

static int
fn2 ()
{
  fn1 (i);
  return 0;
}

static int
fn3 ()
{
  fn2 ();
  return 0;
}

int
main ()
{
  fn3 ();

  if (c[2].f0 != 0) 
    __builtin_abort (); 

  return 0;
}

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