This patch adds is_a <scalar_int_mode> checks to various places
that were explicitly or implicitly restricted to integers already,
in cases where adding an explicit is_a <scalar_int_mode> is useful
for later patches.

In simplify_if_then_else, the:

  GET_MODE (XEXP (XEXP (t, 0), N))

expressions were equivalent to:

  GET_MODE (XEXP (t, 0))

due to the type of operation.

2017-08-30  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* combine.c (sign_extend_short_imm): Add is_a <scalar_int_mode>
	checks.
	(try_combine): Likewise.
	(simplify_if_then_else): Likewise.
	* cse.c (cse_insn): Likewise.
	* dwarf2out.c (mem_loc_descriptor): Likewise.
	* emit-rtl.c (gen_lowpart_common): Likewise.
	* simplify-rtx.c (simplify_truncation): Likewise.
	(simplify_binary_operation_1): Likewise.
	(simplify_const_relational_operation): Likewise.
	(simplify_ternary_operation): Likewise.
	* tree-ssa-loop-ivopts.c (force_expr_to_var_cost): Likewise.

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

From-SVN: r251480