[LLVMbugs] [Bug 19891] New: wrong code by LTO at -O1 (only) on x86_64-linux-gnu (affecting 3.4 and trunk)

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=19891

            Bug ID: 19891
           Summary: wrong code by LTO at -O1 (only) on x86_64-linux-gnu
                    (affecting 3.4 and trunk)
           Product: clang
           Version: unspecified
          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 clang 3.4 miscompile the following code when using
LTO at -O1 (only) on x86_64-linux-gnu in both 32-bit and 64-bit modes.

This is a regression from clang 3.3. 


$ clang-trunk -v
clang version 3.5.0 (trunk 209780)
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 -O1 small.c; a.out
1
$ clang-trunk -flto -O0 small.c; a.out
1
$ clang-3.3 -flto -O1 small.c; a.out
1
$ 
$ clang-trunk -flto -O1 small.c; a.out
0
$ clang-3.4 -flto -O1 small.c; a.out
0
$ 


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


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

int a = 1, c = 1, d;
volatile int b;

int
fn1 ()
{
  for (; d < 1; d++)
    a = 0;
  if (1 & 1 << b)
    for (;;)
      {
    if (a)
      break;
    return 0;
      }
  else
    c = 0;
  return 1;
}

int
main ()
{
  fn1 ();
  printf ("%d\n", c);
  return 0;
}

-- 
You are receiving this mail because:
You are on the CC list for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-bugs/attachments/20140529/3ea2b3ce/attachment.html>