tree-ssanames: Allow non-SSA_NAME arguments to get_range_info

tree-ssanames: Allow non-SSA_NAME arguments to get_range_info

My recent match.pd change required quite a lot of code due to the separate
need to handle INTEGER_CSTs and SSA_NAMEs, and after all, I didn't even
handle one case there, when in x * y / y the x is INTEGER_CST and y is
SSA_NAME.
The following patch allows to simplify it, by allowing non-SSA_NAME argument
to get_range_info, for INTEGER_CSTs it will return VR_RANGE with *min == *max
equal to the constnat, and for non-INTEGER_CST/SSA_NAMEs it will just return
VR_VARYING.

This allows not to simplify just the match.pd, but some other spots too.

2020-11-27  Jakub Jelinek  <jakub@redhat.com>

	* tree-ssanames.c (get_range_info): Handle INTEGER_CST by returning
	VR_RANGE with both *min and *max set to the wide_int value of the
	INTEGER_CST.  Return VR_VARYING for non-SSA_NAMEs.
	* match.pd ((t * 2) / 2) -> t): Handle also @0 being INTEGER_CST.
	Simplify by calling get_range_info on everything.
	* tree-ssa-strlen.c (maybe_diag_stxncpy_trunc): Simplify by calling
	get_range_info on everything.
	* tree-scalar-evolution.c (iv_can_overflow_p): Likewise.