Implement more rtx vector folds on variable-length vectors

Implement more rtx vector folds on variable-length vectors

This patch extends the tree-level folding of variable-length vectors
so that it can also be used on rtxes.  The first step is to move
the tree_vector_builder new_unary/binary_operator routines to the
parent vector_builder class (which in turn means adding a new
template parameter).  The second step is to make simplify-rtx.c
use a direct rtx analogue of the VECTOR_CST handling in fold-const.c.

2019-07-29  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* vector-builder.h (vector_builder): Add a shape template parameter.
	(vector_builder::new_unary_operation): New function, generalizing
	the old tree_vector_builder function.
	(vector_builder::new_binary_operation): Likewise.
	(vector_builder::binary_encoded_nelts): Likewise.
	* int-vector-builder.h (int_vector_builder): Update template
	parameters to vector_builder.
	(int_vector_builder::shape_nelts): New function.
	* rtx-vector-builder.h (rtx_vector_builder): Update template
	parameters to vector_builder.
	(rtx_vector_builder::shape_nelts): New function.
	(rtx_vector_builder::nelts_of): Likewise.
	(rtx_vector_builder::npatterns_of): Likewise.
	(rtx_vector_builder::nelts_per_pattern_of): Likewise.
	* tree-vector-builder.h (tree_vector_builder): Update template
	parameters to vector_builder.
	(tree_vector_builder::shape_nelts): New function.
	(tree_vector_builder::nelts_of): Likewise.
	(tree_vector_builder::npatterns_of): Likewise.
	(tree_vector_builder::nelts_per_pattern_of): Likewise.
	* tree-vector-builder.c (tree_vector_builder::new_unary_operation)
	(tree_vector_builder::new_binary_operation): Delete.
	(tree_vector_builder::binary_encoded_nelts): Likewise.
	* simplify-rtx.c: Include rtx-vector-builder.h.
	(distributes_over_addition_p): New function.
	(simplify_const_unary_operation)
	(simplify_const_binary_operation): Generalize handling of vector
	constants to include variable-length vectors.
	(test_vector_ops_series): Add more tests.

From-SVN: r273867