licm incorrectly hoists divide out of infinite loop, resulting in floating point exception

[Quuxplusone]

Bugzilla Link	PR12706
Status	RESOLVED FIXED
Importance	P normal
Reported by	Richard Osborne (richard@xmos.com)
Reported on	2012-04-30 12:47:53 -0700
Last modified on	2012-04-30 23:03:12 -0700
Version	trunk
Hardware	PC Linux
CC	llvm-bugs@lists.llvm.org, nlewycky@google.com
Fixed by commit(s)
Attachments	bug.ll (988 bytes, application/octet-stream)
Blocks
Blocked by
See also

Created attachment 8477
bug.ll

Compiling the following at -O1 or above in clang results in the division (a /
b) being hoisted outside the loop and a floating point exception.

#include <stdio.h>

__attribute__((noinline)) int f(int a, int b)
{
  while (1) {
    if (b) {
      printf("%d\n", (a / b));
    }
  }
}

int main()
{
  f(1, 0);
  return 0;
}

I've attached the .ll file just before licm pass is run. The issue can be
recreated using opt -licm bug.ll -S and noticing that the sdiv instruction has
been hoisted before the loop.

[Quuxplusone]

Attached bug.ll (988 bytes, application/octet-stream): bug.ll

[Quuxplusone]

Fixed in r155884. Thanks for the great testcase!