[AArch64] Support vectorising with multiple vector sizes

[AArch64] Support vectorising with multiple vector sizes

This patch makes the vectoriser try mixtures of 64-bit and 128-bit
vector modes on AArch64.  It fixes some existing XFAILs and allows
kernel 24 from the Livermore Loops test to be vectorised (by using
a mixture of V2DF and V2SI).

2019-11-14  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* config/aarch64/aarch64.c (aarch64_vectorize_related_mode): New
	function.
	(aarch64_autovectorize_vector_modes): Also add V4HImode and V2SImode.
	(TARGET_VECTORIZE_RELATED_MODE): Define.

gcc/testsuite/
	* gcc.dg/vect/vect-outer-4f.c: Expect the test to pass on aarch64
	targets.
	* gcc.dg/vect/vect-outer-4g.c: Likewise.
	* gcc.dg/vect/vect-outer-4k.c: Likewise.
	* gcc.dg/vect/vect-outer-4l.c: Likewise.
	* gfortran.dg/vect/vect-8.f90: Expect kernel 24 to be vectorized
	for aarch64.
	* gcc.target/aarch64/vect_mixed_sizes_1.c: New test.
	* gcc.target/aarch64/vect_mixed_sizes_2.c: Likewise.
	* gcc.target/aarch64/vect_mixed_sizes_3.c: Likewise.
	* gcc.target/aarch64/vect_mixed_sizes_4.c: Likewise.

From-SVN: r278243