expander: Fix ICE in maybe_warn_rdwr_sizes [PR96335]

expander: Fix ICE in maybe_warn_rdwr_sizes [PR96335]

The following testcase ICEs in maybe_warn_rdwr_sizes.  The problem is that
the caller uses its fndecl and fntype variables to fill up rdwr_map, and
the fntype in that case is a prototype with the access attribute and all
the checks needed for that performed.  But the maybe_warn_rdwr_sizes
function tries to rediscover fndecl/fntype itself and does it differently
from how the caller did (for fndecl get_callee_fndecl and fntype from that
FUNCTION_DECL, otherwise sets fntype to CALL_EXPR_FN's type).

On the testcase, get_callee_fndecl does find a FUNCTION_DECL because
it does STRIP_NOPS in between.

Instead of trying to rediscover those, this patch just passes them down,
like is done in several other functions.

2020-07-28  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/96335
	* calls.c (maybe_warn_rdwr_sizes): Add FNDECL and FNTYPE arguments,
	instead of trying to rediscover them in the body.
	(initialize_argument_information): Adjust caller.

	* gcc.dg/pr96335.c: New test.