Add basic support for direct_optab internal functions

Add basic support for direct_optab internal functions

This patch adds a concept of internal functions that map directly to an
optab (here called "direct internal functions").  The function can only
be used if the associated optab can be used.

We currently have four functions like that:

- LOAD_LANES
- STORE_LANES
- MASK_LOAD
- MASK_STORE

so the patch converts them to the new infrastructure.  These four
all need different types of optabs, but future patches will add
regular unary and binary ones.

In general we need one or two modes to decide whether an optab is
supported, depending on whether it's a convert_optab or not.
This in turn means that we need up to two types to decide whether
an internal function is supported.  The patch records which types
are needed for each internal function, using -1 if the return type
should be used and N>=0 if the type of argument N should be used.

(LOAD_LANES and STORE_LANES are unusual in that both optab modes
come from the same array type.)

Tested on x86_64-linux-gnu, aarch64-linux-gnu and arm-linux-gnueabi.

gcc/
	* coretypes.h (tree_pair): New type.
	* internal-fn.def (DEF_INTERNAL_OPTAB_FN): New macro.  Use it
	for MASK_LOAD, LOAD_LANES, MASK_STORE and STORE_LANES.
	* internal-fn.h (direct_internal_fn_info): New structure.
	(direct_internal_fn_array): Declare.
	(direct_internal_fn_p, direct_internal_fn): New functions.
	(direct_internal_fn_types, direct_internal_fn_supported_p): Declare.
	* internal-fn.c (not_direct, mask_load_direct, load_lanes_direct)
	(mask_store_direct, store_lanes_direct): New macros.
	(direct_internal_fn_array) New array.
	(get_multi_vector_move): Return the optab handler without asserting
	that it is available.
	(expand_LOAD_LANES): Rename to...
	(expand_load_lanes_optab_fn): ...this and add an optab argument.
	(expand_STORE_LANES): Rename to...
	(expand_store_lanes_optab_fn): ...this and add an optab argument.
	(expand_MASK_LOAD): Rename to...
	(expand_mask_load_optab_fn): ...this and add an optab argument.
	(expand_MASK_STORE): Rename to...
	(expand_mask_store_optab_fn): ...this and add an optab argument.
	(direct_internal_fn_types, direct_optab_supported_p)
	(multi_vector_optab_supported_p, direct_internal_fn_supported_p)
	(direct_internal_fn_supported_p): New functions.
	(direct_mask_load_optab_supported_p): New macro.
	(direct_load_lanes_optab_supported_p): Likewise.
	(direct_mask_store_optab_supported_p): Likewise.
	(direct_store_lanes_optab_supported_p): Likewise.

From-SVN: r230473