PR c++/88335 - Implement P1073R3: Immediate functions
c-family/
	* c-common.h (enum rid): Add RID_CONSTEVAL.
	* c-common.c (c_common_reswords): Add consteval.
cp/
	* cp-tree.h (struct lang_decl_fn): Add immediate_fn_p bit.
	(DECL_IMMEDIATE_FUNCTION_P, SET_DECL_IMMEDIATE_FUNCTION_P): Define.
	(enum cp_decl_spec): Add ds_consteval.
	(fold_non_dependent_expr): Add another tree argument defaulted to
	NULL_TREE.
	* name-lookup.h (struct cp_binding_level): Add immediate_fn_ctx_p
	member.
	* parser.c (cp_keyword_starts_decl_specifier_p): Adjust comments
	for C++11 and C++20 specifiers.  Handle RID_CONSTEVAL.
	(CP_PARSER_FLAGS_ONLY_MUTABLE_OR_CONSTEXPR): Adjust comment.
	(CP_PARSER_FLAGS_CONSTEVAL): New.
	(cp_parser_skip_balanced_tokens): New forward declaration.
	(cp_parser_lambda_declarator_opt): Handle ds_consteval.  Set
	current_binding_level->immediate_fn_ctx_p before parsing parameter
	list if decl-specifier-seq contains consteval specifier.
	(cp_parser_decl_specifier_seq): Handle RID_CONSTEVAL.
	(cp_parser_explicit_instantiation): Diagnose explicit instantiation
	with consteval specifier.
	(cp_parser_init_declarator): For consteval or into flags
	CP_PARSER_FLAGS_CONSTEVAL.
	(cp_parser_direct_declarator): If CP_PARSER_FLAGS_CONSTEVAL, set
	current_binding_level->immediate_fn_ctx_p in the sk_function_parms
	scope.
	(set_and_check_decl_spec_loc): Add consteval entry, formatting fix.
	* call.c (build_addr_func): For direct calls to immediate functions
	use build_address rather than decay_conversion.
	(build_over_call): Evaluate immediate function invocations.
	* error.c (dump_function_decl): Handle DECL_IMMEDIATE_FUNCTION_P.
	* semantics.c (expand_or_defer_fn_1): Use tentative linkage and don't
	call mark_needed for immediate functions.
	* typeck.c (cxx_sizeof_or_alignof_expr): Likewise.  Formatting fix.
	(cp_build_addr_expr_1): Reject taking address of immediate function
	outside of immediate function.
	* decl.c (validate_constexpr_redeclaration): Diagnose consteval
	vs. non-consteval or vice versa redeclaration.  Use
	SET_DECL_IMMEDIATE_FUNCTION_P if new_decl is immediate function.
	(check_tag_decl): Use %qs with keyword string to simplify translation.
	Handle ds_consteval.
	(start_decl): Adjust diagnostics for static or thread_local variables
	in immediate functions.
	(grokfndecl): Call sorry_at on virtual consteval.  Use %qs with keyword
	to string to simplify translation.  Diagnose consteval main.  Use
	SET_DECL_IMMEDIATE_FUNCTION_P for consteval.
	(grokdeclarator): Handle consteval.  Use %qs with keyword strings to
	simplify translation.  Use separate ifs instead of chained else if
	for invalid specifiers.  For constinit clear constinit_p rather than
	constexpr_p.
	* constexpr.c (find_immediate_fndecl): New function.
	(cxx_eval_outermost_constant_expr): Allow consteval calls returning
	void.  Diagnose returning address of immediate function from consteval
	evaluation.
	(fold_non_dependent_expr_template): Add OBJECT argument, pass it
	through to cxx_eval_outermost_constant_expr.
	(fold_non_dependent_expr): Add OBJECT argument, pass it through to
	fold_non_dependent_expr_template.
	(fold_non_dependent_init): Adjust fold_non_dependent_expr_template
	caller.
	* method.c (defaulted_late_check): Adjust diagnostics for consteval.
	* lambda.c (maybe_add_lambda_conv_op): Copy over
	DECL_DECLARED_CONSTEXPR_P and DECL_IMMEDIATE_FUNCTION_P bits from
	callop to both artificial functions.
	* init.c (build_value_init): Don't do further processing if
	build_special_member_call returned a TREE_CONSTANT.  Formatting fix.
testsuite/
	* g++.dg/cpp2a/consteval1.C: New test.
	* g++.dg/cpp2a/consteval2.C: New test.
	* g++.dg/cpp2a/consteval3.C: New test.
	* g++.dg/cpp2a/consteval4.C: New test.
	* g++.dg/cpp2a/consteval5.C: New test.
	* g++.dg/cpp2a/consteval6.C: New test.
	* g++.dg/cpp2a/consteval7.C: New test.
	* g++.dg/cpp2a/consteval8.C: New test.
	* g++.dg/cpp2a/consteval9.C: New test.
	* g++.dg/cpp2a/consteval10.C: New test.
	* g++.dg/cpp2a/consteval11.C: New test.
	* g++.dg/cpp2a/consteval12.C: New test.
	* g++.dg/cpp2a/consteval13.C: New test.
	* g++.dg/cpp2a/consteval14.C: New test.
	* g++.dg/ext/consteval1.C: New test.

From-SVN: r277733