rs6000: Add vgnb

rs6000: Add vgnb

Add support for the vgnb instruction, which gathers every Nth bit
per vector element.

[gcc]

2020-05-11  Kelvin Nilsen  <kelvin@gcc.gnu.org>
	    Bill Schmidt  <wschmidt@linux.ibm.com>

	* config/rs6000/altivec.h (vec_gnb): New #define.
	* config/rs6000/altivec.md (UNSPEC_VGNB): New constant.
	(vgnb): New insn.
	* config/rs6000/rs6000-builtin.def (BU_FUTURE_OVERLOAD_1): New
	#define.
	(BU_FUTURE_OVERLOAD_2): Likewise.
	(BU_FUTURE_OVERLOAD_3): Likewise.
	(__builtin_altivec_gnb): New built-in function.
	(__buiiltin_vec_gnb): New overloaded built-in function.
	* config/rs6000/rs6000-call.c (altivec_overloaded_builtins):
	Define overloaded forms of __builtin_vec_gnb.
	(rs6000_expand_binop_builtin): Add error checking for 2nd argument
	of __builtin_vec_gnb.
	(builtin_function_type): Mark return value and arguments unsigned
	for FUTURE_BUILTIN_VGNB.
	* doc/extend.texi (PowerPC AltiVec Built-in Functions Available
	for a Future Architecture): Add description of vec_gnb built-in
	function.

[gcc/testsuite]

2020-05-11  Kelvin Nilsen  <kelvin@gcc.gnu.org>
	    Bill Schmidt  <wschmidt@linux.ibm.com>

	* gcc.target/powerpc/vec-gnb-0.c: New test.
	* gcc.target/powerpc/vec-gnb-1.c: New test.
	* gcc.target/powerpc/vec-gnb-10.c: New test.
	* gcc.target/powerpc/vec-gnb-2.c: New test.
	* gcc.target/powerpc/vec-gnb-3.c: New test.
	* gcc.target/powerpc/vec-gnb-4.c: New test.
	* gcc.target/powerpc/vec-gnb-5.c: New test.
	* gcc.target/powerpc/vec-gnb-6.c: New test.
	* gcc.target/powerpc/vec-gnb-7.c: New test.
	* gcc.target/powerpc/vec-gnb-8.c: New test.
	* gcc.target/powerpc/vec-gnb-9.c: New test.