This patch merges loads and stores from D-registers that are of different modes.

Code like this:

    typedef int __attribute__((vector_size(8))) vec;
    struct pair
    {
      vec v;
      double d;
    }

Now generates a store pair instruction:

    void
    assign (struct pair *p, vec v)
    {
      p->v = v;
      p->d = 1.0;
    }

Whereas previously it generated two `str` instructions.

This patch also merges storing of double zero values with
long integer values:

    struct pair
    {
      long long l;
      double d;
    }

    void
    foo (struct pair *p)
    {
      p->l = 10;
      p->d = 0.0;
    }

Now generates a single store pair instruction rather than two `str` instructions.

The patch basically generalises the mode iterators on the patterns in aarch64.md
and the peepholes in aarch64-ldpstp.md to take all combinations of pairs of modes
so, while it may be a large-ish patch, it does fairly mechanical stuff.

2018-05-22  Jackson Woodruff  <jackson.woodruff@arm.com>
            Kyrylo Tkachov  <kyrylo.tkachov@arm.com>

	* config/aarch64/aarch64.md: New patterns to generate stp
	and ldp.
	(store_pair_sw, store_pair_dw): New patterns to generate stp for
	single words and double words.
	(load_pair_sw, load_pair_dw): Likewise.
	(store_pair_sf, store_pair_df, store_pair_si, store_pair_di):
	Delete.
	(load_pair_sf, load_pair_df, load_pair_si, load_pair_di):
	Delete.
	* config/aarch64/aarch64-ldpstp.md: Modify peephole
	for different mode ldpstp and add peephole for merged zero stores.
	Likewise for loads.
	* config/aarch64/aarch64.c (aarch64_operands_ok_for_ldpstp):
	Add size check.
	(aarch64_gen_store_pair): Rename calls to match new patterns.
	(aarch64_gen_load_pair): Rename calls to match new patterns.
	* config/aarch64/aarch64-simd.md (load_pair<mode>): Rename to...
	(load_pair<DREG:mode><DREG2:mode>): ... This.
	(store_pair<mode>): Rename to...
	(vec_store_pair<DREG:mode><DREG2:mode>): ... This.
	* config/aarch64/iterators.md (DREG, DREG2, DX2, SX, SX2, DSX):
	New mode iterators.
	(V_INT_EQUIV): Handle SImode.
	* config/aarch64/predicates.md (aarch64_reg_zero_or_fp_zero):
	New predicate.

	* gcc.target/aarch64/ldp_stp_6.c: New.
	* gcc.target/aarch64/ldp_stp_7.c: New.
	* gcc.target/aarch64/ldp_stp_8.c: New.

Co-Authored-By: Kyrylo Tkachov <kyrylo.tkachov@arm.com>

From-SVN: r260538