[AArch64] Add scatter stores for partial SVE modes

[AArch64] Add scatter stores for partial SVE modes

This patch adds support for scatter stores of partial vectors,
where the vector base or offset elements can be wider than the
elements being stored.

2019-11-16  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* config/aarch64/aarch64-sve.md
	(scatter_store<SVE_FULL_SD:mode><v_int_equiv>): Extend to...
	(scatter_store<SVE_24:mode><v_int_container>): ...this.
	(mask_scatter_store<SVE_FULL_S:mode><v_int_equiv>): Extend to...
	(mask_scatter_store<SVE_4:mode><v_int_equiv>): ...this.
	(mask_scatter_store<SVE_FULL_D:mode><v_int_equiv>): Extend to...
	(mask_scatter_store<SVE_2:mode><v_int_equiv>): ...this.
	(*mask_scatter_store<mode><v_int_container>_<su>xtw_unpacked): New
	pattern.
	(*mask_scatter_store<SVE_FULL_D:mode><v_int_equiv>_sxtw): Extend to...
	(*mask_scatter_store<SVE_2:mode><v_int_equiv>_sxtw): ...this.
	(*mask_scatter_store<SVE_FULL_D:mode><v_int_equiv>_uxtw): Extend to...
	(*mask_scatter_store<SVE_2:mode><v_int_equiv>_uxtw): ...this.

gcc/testsuite/
	* gcc.target/aarch64/sve/scatter_store_1.c (TEST_LOOP): Start at 0.
	(TEST_ALL): Add tests for 8-bit and 16-bit elements.
	* gcc.target/aarch64/sve/scatter_store_2.c: Update accordingly.
	* gcc.target/aarch64/sve/scatter_store_3.c (TEST_LOOP): Start at 0.
	(TEST_ALL): Add tests for 8-bit and 16-bit elements.
	* gcc.target/aarch64/sve/scatter_store_4.c: Update accordingly.
	* gcc.target/aarch64/sve/scatter_store_5.c (TEST_LOOP): Start at 0.
	(TEST_ALL): Add tests for 8-bit, 16-bit and 32-bit elements.
	* gcc.target/aarch64/sve/scatter_store_8.c: New test.
	* gcc.target/aarch64/sve/scatter_store_9.c: Likewise.

From-SVN: r278347