ipa-cp: Avoid long linear searches through DECL_ARGUMENTS

ipa-cp: Avoid long linear searches through DECL_ARGUMENTS

There have been concerns that linear searches through DECL_ARGUMENTS
that are often necessary to compute the index of a particular
PARM_DECL which is the key to results of IPA-CP can happen often
enough to be a compile time issue, especially if we plug the results
into value numbering, as I intend to do with a follow-up patch.

This patch creates a vector sorted according to PARM_DECLs to do the look-up
for all functions which have some information discovered by IPA-CP and which
have 32 parameters or more.  32 is a hard-wired magical constant here to
capture the trade-off between the memory allocation overhead and length of the
linear search.  I do not think it is worth making it a --param but if people
think it appropriate, I can turn it into one.

gcc/ChangeLog:

2023-05-31  Martin Jambor  <mjambor@suse.cz>

	* ipa-prop.h (ipa_uid_to_idx_map_elt): New type.
	(struct ipcp_transformation): Rearrange members	according to
	C++ class coding convention, add m_uid_to_idx,
	get_param_index and maybe_create_parm_idx_map.
	* ipa-cp.cc (ipcp_transformation::get_param_index): New function.
	(compare_uids): Likewise.
	(ipcp_transformation::maype_create_parm_idx_map): Likewise.
	* ipa-prop.cc (ipcp_get_parm_bits): Use get_param_index.
	(ipcp_update_bits): Accept TS as a parameter, assume it is not NULL.
	(ipcp_update_vr): Likewise.
	(ipcp_transform_function): Call, maybe_create_parm_idx_map of TS, bail
	out quickly if empty, pass it to ipcp_update_bits and ipcp_update_vr.