tree-ssa-math-opts: Pattern recognize yet another .ADD_OVERFLOW pattern [PR113982]

tree-ssa-math-opts: Pattern recognize yet another .ADD_OVERFLOW pattern [PR113982]

We pattern recognize already many different patterns, and closest to the
requested one also
   yc = (type) y;
   zc = (type) z;
   x = yc + zc;
   w = (typeof_y) x;
   if (x > max)
where y/z has the same unsigned type and type is a wider unsigned type
and max is maximum value of the narrower unsigned type.
But apparently people are creative in writing this in diffent ways,
this requests
   yc = (type) y;
   zc = (type) z;
   x = yc + zc;
   w = (typeof_y) x;
   if (x >> narrower_type_bits)

The following patch implements that.

2024-05-13  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/113982
	* tree-ssa-math-opts.cc (arith_overflow_check_p): Also return 1
	for RSHIFT_EXPR by precision of maxval if shift result is only
	used in a cast or comparison against zero.
	(match_arith_overflow): Handle the RSHIFT_EXPR use case.

	* gcc.dg/pr113982.c: New test.