[ARC] Fix unwanted match for sign extend 16-bit constant.

[ARC] Fix unwanted match for sign extend 16-bit constant.

The combine pass may conclude umulhisi3_imm pattern can accept also sign
extended 16-bit constants. This patch prohibits the combine in considering
this pattern as suitable.

gcc/
2016-04-29  Claudiu Zissulescu  <claziss@synopsys.com>

	* config/arc/arc.h (UNSIGNED_INT12, UNSIGNED_INT16): Define.
	* config/arc/arc.md (umulhisi3): Use arc_short_operand predicate.
	(umulhisi3_imm): Update predicates and constraint letters.
	(umulhisi3_reg): Declare instruction as commutative.
	* config/arc/constraints.md (J12, J16): New constraints.
	* config/arc/predicates.md (short_unsigned_const_operand): New
	predicate.
	(arc_short_operand): Likewise.
	* testsuite/gcc.target/arc/umulsihi3_z.c: New file.

From-SVN: r235623