This patch makes more use of the existing paradoxical_subreg_p
predicate and also adds a version that operates on outer and
inner modes.

Some of the affected tests were based on GET_MODE_SIZE rather than
GET_MODE_PRECISION and so the patch could change the result for modes
that have the same size but different precisions.  I think in each
case the change should be a no-op or more correct, since a mode with
precision N bits can't be expected to hold all of a mode with precision
M>N bits.

The patch changes the branch taken in simplify_subreg for modes with
equal precision, but the new form matches the commentary more closely.
Both branches should be equally good in that situation.

2017-08-22  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* rtl.h (paradoxical_subreg_p): Define inline, and add a version
	that takes the outer and inner modes.
	* doc/rtl.texi: Use paradoxical_subreg_p instead of a GET_MODE_SIZE
	comparison as the canonical test for a paradoxical subreg.
	* combine.c (simplify_set): Use paradoxical_subreg_p.
	(make_extraction): Likewise.
	(force_to_mode): Likewise.
	(rtx_equal_for_field_assignment_p): Likewise.
	(gen_lowpart_for_combine): Likewise.
	(simplify_comparison): Likewise.
	* cse.c (equiv_constant): Likewise.
	* expmed.c (store_bit_field_1): Likewise.
	* final.c (alter_subreg): Likewise.
	* fwprop.c (propagate_rtx): Likewise.
	(forward_propagate_subreg): Likewise.
	* ira-conflicts.c (ira_build_conflicts): Likewise.
	* lower-subreg.c (simplify_gen_subreg_concatn): Likewise.
	* lra-constraints.c (curr_insn_transform): Likewise.
	(split_reg): Likewise.
	* lra-eliminations.c (move_plus_up): Likewise.
	(lra_eliminate_regs_1): Likewise.
	* recog.c (general_operand): Likewise.
	* ree.c (combine_reaching_defs): Likewise.
	* reload.c (push_reload): Likewise.
	(find_reloads): Likewise.
	* reload1.c (elimination_effects): Likewise.
	(compute_reload_subreg_offset): Likewise.
	(choose_reload_regs): Likewise.
	* rtlanal.c (subreg_lsb_1): Likewise.
	* simplify-rtx.c (simplify_unary_operation_1): Likewise.
	(simplify_subreg): Likewise.
	* var-tracking.c (track_loc_p): Likewise.
	* emit-rtl.c (byte_lowpart_offset): Likewise.
	(paradoxical_subreg_p): Delete out-of-line definition.

Co-Authored-By: Alan Hayward <alan.hayward@arm.com>
Co-Authored-By: David Sherwood <david.sherwood@arm.com>

From-SVN: r251282