[LLVMbugs] [Bug 20856] New: wrong code (FP exception) at -O3 on x86_64-linux-gnu (affecting 3.4.1 and later)

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=20856

            Bug ID: 20856
           Summary: wrong code (FP exception) at -O3 on x86_64-linux-gnu
                    (affecting 3.4.1 and later)
           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 -O3 on
x86_64-linux-gnu (in both 32-bit and 64-bit modes). 

This is a regression from 3.4.

$ clang-trunk -v
clang version 3.6.0 (trunk 216814)
Target: x86_64-unknown-linux-gnu
Thread model: posix
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/4.8
Found candidate GCC installation: /usr/lib/gcc/i686-linux-gnu/4.8.1
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/4.6.4
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 -O2 small.c; a.out
$ clang-3.4 -O3 small.c; a.out
$ 
$ clang-trunk -O3 small.c
$ ./a.out
Floating point exception (core dumped)
$ 

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

int a, b, *d, g, i, **j;
short *f;
static char c;

struct
{
  int f2;
} e;

void
fn1 (char *p)
{
  i = a / *p;
}

void
fn2 (int p)
{
  short h;
  fn1 (&c);
  f = &h;
  for (; g < 1; g++)
    if (c && p)
      *j = 0;
}

void
fn3 (int *p)
{
  fn2 (*p);
}

void
fn4 ()
{
  b = 0;
  for (c = -7; c; c++)
    {
      fn3 (&b);
      for (; e.f2;)
    *d = 0;
    }
}

int
main ()
{
  fn4 ();
  return 0;
}

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