[LLVMbugs] [Bug 21032] New: wrong code (that hangs) at -O2 and -O3 on x86_64-linux-gnu

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=21032

            Bug ID: 21032
           Summary: wrong code (that hangs) at -O2 and -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: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

The following code is miscompiled by the current clang trunk on
x86_64-linux-gnu at -O2 and -O3 in the 64-bit mode (but not in the 32-bit
mode). 

This is regression from 3.5.0.

Possibly related to PR 21030? 

$ clang-trunk -v
clang version 3.6.0 (trunk 218236)
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 -m32 -O2 small.c; a.out
$ clang-trunk -m32 -O3 small.c; a.out
$ clang-trunk -m64 -O1 small.c; a.out
$ clang-3.5.0 -m64 -O2 small.c; a.out
$ 
$ clang-trunk -m64 -O2 small.c
$ timeout -s 9 10 ./a.out
Killed
$ 

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

int a, c, d, e;
long b;

int
fn1 (short p1, int p2)
{
  return p2 == 0 || (p1 && p2 == p1);
}

void
fn2 (int p)
{
  e = fn1 (p ^ 1, p);
  c = e || c;
}

int
main ()
{
  for (a = -1; a > -25; --a)
    {
      int f = a;
      unsigned int g = f;
      d = g != b;
      fn2 (f);
    }
  return 0;
}

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