[LLVMbugs] [Bug 21582] New: wrong code at -O1 and above on x86_64-linux-gnu

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=21582

            Bug ID: 21582
           Summary: wrong code at -O1 and above 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: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

The current clang trunk miscompiles the following code at -O1 and above on
x86_64-linux-gnu in both 32-bit and 64-bit modes.

This also affects 3.5.0, and is a regression from 3.4.x. 

$ clang-trunk -v
clang version 3.6.0 (trunk 220897)
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/4.6.4
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/4.8.1
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.8
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Selected multilib: .;@m64
$ 
$ clang-trunk -O0 small.c; a.out
1
$ clang-3.4.2 -O1 small.c; a.out
1
$ 
$ clang-trunk -O1 small.c; a.out
0
$ clang-3.5.0 -O1 small.c; a.out
0
$


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


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

int a, b, c, e, k, l;

struct
{
  int f1;
} d;

void
fn1 ()
{
  if (d.f1)
    for (c = 0; a;)
      for (; l;)
    ;
}

int
fn2 ()
{
  for (; b < 1; b++)
    for (; k; k++)
      fn1 ();
  return 0;
}

int
fn3 ()
{
  int g = 0, h;
  int i[1][1] = { {1} };
  for (;;)
    {
      b = 0;
      for (; g < 1; g++)
    h = i[0][g] != fn2 ();
      if (++e)
    return 0;
      g = h;
    }
}

int
main ()
{
  fn3 ();
  printf ("%d\n", b);
  return 0;
}

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