This patch generalises various places that used hwi tree accessors so
that they can handle poly_ints instead.  In many cases these changes
are by inspection rather than because something had shown them to be
necessary.

I think the alias.c part is a minor bug fix: previously we used
fits_uhwi_p for a signed HOST_WIDE_INT (which the caller does
treat as signed rather than unsigned).  We also checked whether
each individual offset overflowed but didn't check whether the
sum did.

2018-05-30  Richard Sandiford  <richard.sandiford@linaro.org>

gcc/
	* alias.c (adjust_offset_for_component_ref): Use poly_int_tree_p
	and wi::to_poly_offset.  Add the current offset and then check
	whether the sum fits, rather than using an unchecked addition of
	a checked term.  Check for a shwi rather than a uhwi.
	* expr.c (get_bit_range): Use tree_to_poly_uint64.
	(store_constructor): Use poly_int_tree_p.
	(expand_expr_real_1): Likewise.
	* function.c (assign_temp): Likewise.
	* fold-const.c (const_binop): Use poly_int_tree_p and
	wi::to_poly_offset.
	(fold_indirect_ref_1): Likewise.  Use multiple_p to attempt an exact
	division.
	* ipa-icf-gimple.c (func_checker::compare_operand): Use
	to_poly_offset for MEM offsets.
	* ipa-icf.c (sem_variable::equals): Likewise.
	* stor-layout.c (compute_record_mode): Use poly_int_tree_p.
	* tree-ssa-sccvn.c (ao_ref_init_from_vn_reference): Use
	wi::to_poly_offset for BIT_FIELD_REF offsets.
	(vn_reference_maybe_forwprop_address): Use poly_int_tree_p and
	wi::to_poly_offset.
	* var-tracking.c (emit_note_insn_var_location): Use
	tree_to_poly_uint64.

From-SVN: r260914