[LLVMbugs] [Bug 19225] New: wrong code by LTO at -Os (only) on x86_64-linux-gnu (affecting trunk and 3.4)

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=19225

            Bug ID: 19225
           Summary: wrong code by LTO at -Os (only) on x86_64-linux-gnu
                    (affecting trunk and 3.4)
           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
-Os on x86_64-linux-gnu in both 32-bit and 64-bit modes. The generated code
hangs. 

This is a regression from clang 3.3.


$ clang-trunk -v
clang version 3.5.0 (trunk 204459)
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 -Os small.c; a.out
$ clang-trunk -flto -O1 small.c; a.out
$ clang-trunk -flto -O2 small.c; a.out
$ clang-3.3 -flto -Os small.c; a.out
$
$ clang-trunk -flto -Os small.c
$ a.out
^C
$ clang-3.4 -flto -Os small.c
$ a.out
^C
$


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


int *a, b, c, e, **f = &a;
long long d = -1;

static int *
fn1 (long long p)
{ 
  int g;
  if (d < 0)
    for (b = 1; b >=0; b--)
      { 
        int h = p;
        g = h == 0 ? 0 : 2 % h;
        e = g || c;
      }
  return 0;
}

int
main ()
{ 
  fn1 (a == 0);
  return 0;
}

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