PR middle-end/87041 - -Wformat reading through null pointer on unreachable code

gcc/ChangeLog:

	PR middle-end/87041
	* gimple-ssa-sprintf.c (format_directive): Use %G to include
	inlining context.
	(sprintf_dom_walker::compute_format_length):
	Avoid setting POSUNDER4K here.
	(get_destination_size): Handle null argument values.
	(get_user_idx_format): New function.
	(sprintf_dom_walker::handle_gimple_call): Handle all printf-like
	functions, including user-defined with attribute format printf.
	Use %G to include inlining context.
	Set POSUNDER4K here.

gcc/c-family/ChangeLog:

	PR middle-end/87041
	* c-format.c (check_format_types): Avoid diagnosing null pointer
	arguments to printf-family of functions.

gcc/testsuite/ChangeLog:

	PR middle-end/87041
	* gcc.c-torture/execute/fprintf-2.c: New test.
	* gcc.c-torture/execute/printf-2.c: Same.
	* gcc.c-torture/execute/user-printf.c: Same.
	* gcc.dg/tree-ssa/builtin-fprintf-warn-1.c: Same.
	* gcc.dg/tree-ssa/builtin-printf-2.c: Same.
	* gcc.dg/tree-ssa/builtin-printf-warn-1.c: Same.
	* gcc.dg/tree-ssa/user-printf-warn-1.c: Same.

From-SVN: r265648