[LLVMbugs] [Bug 20237] New: wrong code by LTO at -O1, -Os, and -O2 on x86_64-linux-gnu (affecting 3.4 and trunk in 64-bit mode)

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=20237

            Bug ID: 20237
           Summary: wrong code by LTO at -O1, -Os, and -O2 on
                    x86_64-linux-gnu (affecting 3.4 and trunk in 64-bit
                    mode)
           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 and 3.4 miscompile the following code when using LTO at
-O1, Os, and -O2 on x86_64-linux-gnu in 64-bit mode (but not in 32-bit mode). 

This is regression from 3.3. 

$ clang-trunk -v
clang version 3.5.0 (trunk 212424)
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 -m64 -O1 small.c; a.out
1
$ clang-trunk -flto -m32 -O1 small.c; a.out
1
$ clang-3.3 -flto -m64 -O1 small.c; a.out
1
$ 
$ clang-trunk -flto -m64 -O1 small.c; a.out
0
$ clang-3.4 -flto -m64 -O1 small.c; a.out
0
$ 


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


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

int a, b, d, e, g, i;

struct S0
{
  int f0;
  int f1;
} c;

struct S1
{
  int f0;
} f, h = {1};

int
fn1 (struct S0 p1)
{
  return p1.f0;
}

void
fn2 (int p1, struct S1 p2)
{
  int j = e; 
  for (e = 1; e; e = j)
    {
      if (c.f1)
    b = 0;
      else
    {
      i = 1 >> a;
      if (!i)
        fn2 (0, f);
      b = p2.f0 || p1 | d;
    }
      p2 = h;
    }
}

int
main ()
{
  g = fn1 (c);
  if (!g)
    for (; c.f1; --c.f1);
  fn2 (1, f);
  printf ("%d\n", b);
  return 0;
}

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