match.pd: Optimize ((cst << x) & 1) [PR96669]

match.pd: Optimize ((cst << x) & 1) [PR96669]

While we had a ((1 << x) & 1) != 0 to x == 0 optimization already,
this patch adds ((cst << x) & 1) optimization too, this time the
second constant must be 1 though, not some power of two, but the first
one can be any constant.  If it is even, the result is false, if it is
odd, the result is x == 0.

2021-01-16  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/96669
	* match.pd ((CST << x) & 1 -> x == 0): New simplification.

	* gcc.dg/tree-ssa/pr96669-1.c: Adjust regexp.
	* gcc.dg/tree-ssa/pr96669-2.c: New test.