Extend can_duplicate_and_interleave_p to mixed-size vectors

Extend can_duplicate_and_interleave_p to mixed-size vectors

This patch makes can_duplicate_and_interleave_p cope with mixtures of
vector sizes, by using queries based on get_vectype_for_scalar_type
instead of directly querying GET_MODE_SIZE (vinfo->vector_mode).

int_mode_for_size is now the first check we do for a candidate mode,
so it seemed better to restrict it to MAX_FIXED_MODE_SIZE.  This avoids
unnecessary work and avoids trying to create scalar types that the
target might not support.

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

gcc/
	* tree-vectorizer.h (can_duplicate_and_interleave_p): Take an
	element type rather than an element mode.
	* tree-vect-slp.c (can_duplicate_and_interleave_p): Likewise.
	Use get_vectype_for_scalar_type to query the natural types
	for a given element type rather than basing everything on
	GET_MODE_SIZE (vinfo->vector_mode).  Limit int_mode_for_size
	query to MAX_FIXED_MODE_SIZE.
	(duplicate_and_interleave): Update call accordingly.
	* tree-vect-loop.c (vectorizable_reduction): Likewise.

From-SVN: r278335