ifcvt: Don't introduce trapping or faulting reads in noce_try_sign_mask [PR106032]

ifcvt: Don't introduce trapping or faulting reads in noce_try_sign_mask [PR106032]

noce_try_sign_mask as documented will optimize
  if (c < 0)
    x = t;
  else
    x = 0;
into x = (c >> bitsm1) & t;
The optimization is done if either t is unconditional
(e.g. for
  x = t;
  if (c >= 0)
    x = 0;
) or if it is cheap.  We already check that t doesn't have side-effects,
but if t is conditional, we need to punt also if it may trap or fault,
as we make it unconditional.

I've briefly skimmed other noce_try* optimizations and didn't find one that
would suffer from the same problem.

2022-06-21  Jakub Jelinek  <jakub@redhat.com>

	PR rtl-optimization/106032
	* ifcvt.cc (noce_try_sign_mask): Punt if !t_unconditional, and
	t may_trap_or_fault_p, even if it is cheap.

	* gcc.c-torture/execute/pr106032.c: New test.