Add gen_(const_)vec_duplicate helpers

Add gen_(const_)vec_duplicate helpers

This patch adds helper functions for generating constant and
non-constant vector duplicates.  These routines help with SVE because
it is then easier to use:

   (const:M (vec_duplicate:M X))

for a broadcast of X, even if the number of elements in M isn't known
at compile time.  It also makes it easier for general rtx code to treat
constant and non-constant duplicates in the same way.

In the target code, the patch uses gen_vec_duplicate instead of
gen_rtx_VEC_DUPLICATE if handling constants correctly is potentially
useful.  It might be that some or all of the call sites only handle
non-constants in practice, in which case the change is a harmless
no-op (and a saving of a few characters).

Otherwise, the target changes use gen_const_vec_duplicate instead
of gen_rtx_CONST_VECTOR if the constant is obviously a duplicate.
They also include some changes to use CONSTxx_RTX for easy global
constants.

2017-11-01  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* emit-rtl.h (gen_const_vec_duplicate): Declare.
	(gen_vec_duplicate): Likewise.
	* emit-rtl.c (gen_const_vec_duplicate_1): New function, split
	out from...
	(gen_const_vector): ...here.
	(gen_const_vec_duplicate, gen_vec_duplicate): New functions.
	(gen_rtx_CONST_VECTOR): Use gen_const_vec_duplicate for constants
	whose elements are all equal.
	* optabs.c (expand_vector_broadcast): Use gen_const_vec_duplicate.
	* simplify-rtx.c (simplify_const_unary_operation): Likewise.
	(simplify_relational_operation): Likewise.
	* config/aarch64/aarch64.c (aarch64_simd_gen_const_vector_dup):
	Likewise.
	(aarch64_simd_dup_constant): Use gen_vec_duplicate.
	(aarch64_expand_vector_init): Likewise.
	* config/arm/arm.c (neon_vdup_constant): Likewise.
	(neon_expand_vector_init): Likewise.
	(arm_expand_vec_perm): Use gen_const_vec_duplicate.
	(arm_block_set_unaligned_vect): Likewise.
	(arm_block_set_aligned_vect): Likewise.
	* config/arm/neon.md (neon_copysignf<mode>): Likewise.
	* config/i386/i386.c (ix86_expand_vec_perm): Likewise.
	(expand_vec_perm_even_odd_pack): Likewise.
	(ix86_vector_duplicate_value): Use gen_vec_duplicate.
	* config/i386/sse.md (one_cmpl<mode>2): Use CONSTM1_RTX.
	* config/ia64/ia64.c (ia64_expand_vecint_compare): Use
	gen_const_vec_duplicate.
	* config/ia64/vect.md (addv2sf3, subv2sf3): Use CONST1_RTX.
	* config/mips/mips.c (mips_gen_const_int_vector): Use
	gen_const_vec_duplicate.
	(mips_expand_vector_init): Use CONST0_RTX.
	* config/powerpcspe/altivec.md (abs<mode>2, nabs<mode>2): Likewise.
	(define_split): Use gen_const_vec_duplicate.
	* config/rs6000/altivec.md (abs<mode>2, nabs<mode>2): Use CONST0_RTX.
	(define_split): Use gen_const_vec_duplicate.
	* config/s390/vx-builtins.md (vec_genmask<mode>): Likewise.
	(vec_ctd_s64, vec_ctd_u64, vec_ctsl, vec_ctul): Likewise.
	* config/spu/spu.c (spu_const): Likewise.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@254292 138bc75d-0d04-0410-961f-82ee72b054a4