This patch changes vec_perm_indices from a plain vec<> to a class
that stores a canonicalized permutation, using the same encoding
as for VECTOR_CSTs.  This means that vec_perm_indices now carries
information about the number of vectors being permuted (currently
always 1 or 2) and the number of elements in each input vector.

A new vec_perm_builder class is used to actually build up the vector,
like tree_vector_builder does for trees.  vec_perm_indices is the
completed representation, a bit like VECTOR_CST is for trees.

The patch just does a mechanical conversion of the code to
vec_perm_builder: a later patch uses explicit encodings where possible.

The point of all this is that it makes the representation suitable
for variable-length vectors.  It's no longer necessary for the
underlying vec<>s to store every element explicitly.

In int-vector-builder.h, "using the same encoding as tree and rtx constants"
describes the endpoint -- adding the rtx encoding comes later.

2018-01-02  Richard Sandiford  <richard.sandiford@linaro.org>

gcc/
	* int-vector-builder.h: New file.
	* vec-perm-indices.h: Include int-vector-builder.h.
	(vec_perm_indices): Redefine as an int_vector_builder.
	(auto_vec_perm_indices): Delete.
	(vec_perm_builder): Redefine as a stand-alone class.
	(vec_perm_indices::vec_perm_indices): New function.
	(vec_perm_indices::clamp): Likewise.
	* vec-perm-indices.c: Include fold-const.h and tree-vector-builder.h.
	(vec_perm_indices::new_vector): New function.
	(vec_perm_indices::new_expanded_vector): Update for new
	vec_perm_indices class.
	(vec_perm_indices::rotate_inputs): New function.
	(vec_perm_indices::all_in_range_p): Operate directly on the
	encoded form, without computing elided elements.
	(tree_to_vec_perm_builder): Operate directly on the VECTOR_CST
	encoding.  Update for new vec_perm_indices class.
	* optabs.c (expand_vec_perm_const): Create a vec_perm_indices for
	the given vec_perm_builder.
	(expand_vec_perm_var): Update vec_perm_builder constructor.
	(expand_mult_highpart): Use vec_perm_builder instead of
	auto_vec_perm_indices.
	* optabs-query.c (can_mult_highpart_p): Use vec_perm_builder and
	vec_perm_indices instead of auto_vec_perm_indices.  Use a single
	or double series encoding as appropriate.
	* fold-const.c (fold_ternary_loc): Use vec_perm_builder and
	vec_perm_indices instead of auto_vec_perm_indices.
	* tree-ssa-forwprop.c (simplify_vector_constructor): Likewise.
	* tree-vect-data-refs.c (vect_grouped_store_supported): Likewise.
	(vect_permute_store_chain): Likewise.
	(vect_grouped_load_supported): Likewise.
	(vect_permute_load_chain): Likewise.
	(vect_shift_permute_load_chain): Likewise.
	* tree-vect-slp.c (vect_build_slp_tree_1): Likewise.
	(vect_transform_slp_perm_load): Likewise.
	(vect_schedule_slp_instance): Likewise.
	* tree-vect-stmts.c (perm_mask_for_reverse): Likewise.
	(vectorizable_mask_load_store): Likewise.
	(vectorizable_bswap): Likewise.
	(vectorizable_store): Likewise.
	(vectorizable_load): Likewise.
	* tree-vect-generic.c (lower_vec_perm): Use vec_perm_builder and
	vec_perm_indices instead of auto_vec_perm_indices.  Use
	tree_to_vec_perm_builder to read the vector from a tree.
	* tree-vect-loop.c (calc_vec_perm_mask_for_shift): Take a
	vec_perm_builder instead of a vec_perm_indices.
	(have_whole_vector_shift): Use vec_perm_builder and
	vec_perm_indices instead of auto_vec_perm_indices.  Leave the
	truncation to calc_vec_perm_mask_for_shift.
	(vect_create_epilog_for_reduction): Likewise.
	* config/aarch64/aarch64.c (expand_vec_perm_d::perm): Change
	from auto_vec_perm_indices to vec_perm_indices.
	(aarch64_expand_vec_perm_const_1): Use rotate_inputs on d.perm
	instead of changing individual elements.
	(aarch64_vectorize_vec_perm_const): Use new_vector to install
	the vector in d.perm.
	* config/arm/arm.c (expand_vec_perm_d::perm): Change
	from auto_vec_perm_indices to vec_perm_indices.
	(arm_expand_vec_perm_const_1): Use rotate_inputs on d.perm
	instead of changing individual elements.
	(arm_vectorize_vec_perm_const): Use new_vector to install
	the vector in d.perm.
	* config/powerpcspe/powerpcspe.c (rs6000_expand_extract_even):
	Update vec_perm_builder constructor.
	(rs6000_expand_interleave): Likewise.
	* config/rs6000/rs6000.c (rs6000_expand_extract_even): Likewise.
	(rs6000_expand_interleave): Likewise.

From-SVN: r256095