gcc/c-family/
	* c-cppbuiltin.c (c_cpp_builtins): Use new feature test values for
	concepts when -std=c++2a. Bump __cpp_concepts to 201907.
	* c.opt: Add -Wconcepts-ts.
	* c-opts.c (c_common_post_options): Warn when -fconcepts is used
	with -std=c++2a. Disable warning for -fconcepts in C++20 mode.
	(set_std_cxx2a): Enable concepts by default.
gcc/cp/
	* call.c (build_new_function_call): Don't evaluate concepts here.
	(constraint_failure): Don't record the template.
	(print_z_candidate): Don't extract the template.
	* class.c (add_method): When overloading, hide ineligible special
	member fns.
	(check_methods): Set TYPE_HAS_COMPLEX_* here.
	* constexpr.c (cxx_eval_constant_expression): Evaluate concepts.
	(maybe_initialize_fundef_copies_table): Remove.
	(get_fundef_copy): Use hash_map_safe_get_or_insert.
	(clear_cv_and_fold_caches): Clear the satisfaction cache.
	* constraint.cc (known_non_bool_p): New.
	(parsing_constraint_expression_sentinel): Renamed from
	expanding_constraint_sentinel.
	(check_constraint_operands): New.
	(check_constraint_atom): New.
	(finish_constraint_binary_op): New.
	(finish_constraint_or_expr): Likewise.
	(finish_constraint_and_expr): Likewise.
	(finish_constraint_primary_expr): Likewise.
	(combine_constraint_expressions): New.
	(finish_requires_expr): Add location parm.
	(get_concept_definition): Return the initializer of concept definitions.
	(get_template_head_requirements): New.
	(get_trailing_function_requirements): New.
	(deduce_constrained_parameter): Check if the identifier or template-id
	is a concept definition.
	(resolve_concept_definition_check): Removed.
	(resolve_variable_concept_check): Removed.
	(resolve_concept_check): New.
	(resolve_constraint_check): Handle concept definitions.
	converting arguments.
	(function_concept_check_p): Removed.
	(variable_concept_check_p): Removed.
	(unpack_concept_check): New.
	(get_concept_check_template): New.
	(build_call_check): Moved and renamed to build_function_check.
	(build_concept_check_arguments): make static.
	(build_function_check): Always do overload resolution
	in order to force conversion of template arguments (i.e., actually
	check that the use of a concept is valid).
	(build_standard_check): Renamed from build_real_concept_check.
	(build_real_concept_check): Build checks for C++2a concepts by
	(build_wildcard_concept_check): New.
	(build_concept_check): Use build_real_concept_check. New overload.
	(build_constraints): Save expressions, not normalized constraints.
	(build_concept_id): New. Pass tf_warning_or_error.
	(build_type_constraint): New.
	(finish_type_constraints): New.
	(associate_classtype_constraints): Also add constraints to union
	types. Note the original declaration in errors. Don't return
	error_mark_node in order to avoid an assertion later.
	(push_down_pack_expansion): Remove.
	(finish_shorthand_constraint): Make fold expressions, not naked
	parameter packs. Always apply the constraint to each template argument.
	(check_introduction_list): New. Fail if not enough
	names are introduced.
	(finish_template_introduction): Don't normalize constraints. Pass
	tsubst flags. Check for insufficient introductions.
	(placeholder_extract_concept_and_args): Handle the template-id case.
	Unpack function concept checks correctly.
	(tsubst_simple_requirement): Return errors if they occur. Don't
	process as a template.
	(tsubst_type_requirement): Likewise.
	(type_deducible_p): New. Wrap the input expression in parens for the
	purpose of deduction.
	(expression_convertible_t): New.
	(tsubst_compound_requirement): Use new deduction, conversion predicates.
	(tsubst_nested_requirement): Return errors if they occur. Don't
	process as a template. Instantiate and evaluate the nested requirement.
	(tsubst_valid_expression_requirement): New.
	(tsubst_simple_requirement): Use tsubst_valid_expression_requirement.
	(tsubst_compound_requirement): Use tsubst_valid_expression_requirement.
	(check_constaint_variables): New.
	(tsubst_constraint_variables): Check that type substitutions are valid.
	(tsubst_requires_expr): Likewise. Produce new requires-exprs during
	template substitution. Copy the previous local specialization stack,
	so references to non-local parameters can be found. Use cp_unevaluated.
	(tsubst_constraint): New. Don't evaluate concept checks.
	(subst_info): New.
	(norm_info): New. Used to build a normalization tree for concept check
	diagnostics.
	(debug_parameter_mapping): New.
	(debug_argument_list): New.
	(expand_concept): Removed.
	(normalize_logical_operation): Pass subst_info through call.
	(normalize_pack_expansion): Remove.
	(normalize_simple_requirement): Removed
	(normalize_type_requirement): Removed
	(normalize_compound_requirement): Removed
	(normalize_nested_requirement): Removed
	(normalize_requirement): Removed
	(normalize_requirements): Removed
	(normalize_requires_expression): Removed
	(normalize_variable_concept_check): Removed.
	(normalize_function_concept_check): Removed.
	(normalize_concept_check): Merged all normalize_*_check here.
	Substitute through written template arguments before normalizing the
	definition. Only substitute the innermost template arguments.
	(check_for_logical_overloads): Delete.
	(map_arguments): New. Associate template parameters with arguments.
	(build_parameter_mapping): New. Extract used parameters.
	(normalize_expression): Rewrite.
	(normalize_conjunction): Removed
	(normalize_disjunction): Removed
	(normalize_predicate_constraint): Removed
	(normalize_parameterized_constraint): Removed
	(normalized_map): New variable.
	(get_normalized_constraints): New entry point for normalization.
	Establishes a timer.
	(get_normalized_constraints_from_info): New.
	(get_normalized_constraints_from_decl): New. Turn on template processing
	prior to normalization. Handle inheriting ctors. Build the
	normalization arguments from the full set of template parameters of the
	most general template. This guarantees that we have no concrete arguments
	in the parameter mapping (e.g., from template members of class
	templates). Cache normalizations.
	(normalize_concept_definition): New. Cache normalizations.
	(normalize_template_requirements): New.
	(normalize_nontemplate_requirements): New.
	(normalize_constraint_expression): New.
	(tsubst_parameter_mapping): New.
	(get_mapped_args): New.
	(parameter_mapping_equivalent_p): New. Use template_args_equal.
	(atomic_constraints_identical_p): New.
	(hash_atomic_constraint): New.
	(satisfying_constraint_p): New. Guard against recursive evaluation of
	constraints during satisfaction.
	(satisfy_conjunction): New.
	(satisfy_disjunction): New.
	(sat_entry): New class for hashing satisfaction results.
	(sat_hasher): New hash traits.
	(sat_cache): New.
	(get_satisfaction): New. Returns cached satisfaction result.
	(save_satisfaction): New. Caches a satisfaction result.
	(clear_satisfaction_cache): New.
	(satisfaction_cache): New. Helps manage satisfaction cache requests.
	(decl_satisfied_cache): New.
	(satisfy_atom): New.
	(satisfy_constraint_r): New.
	(satisfy_constraint): Use new satisfaction algorithm.
	(evaluate_concept_check): New.
	(evaluate_concept): Removed.
	(evaluate_function_concept): Removed.
	(evaluate_variable_concept): Removed.
	(satisfy_constraint_expression): New.
	(constraint_expression_satisfied_p): New.
	(constraints_satisfied_p): Use strip_inheriting_ctors. Use
	push_/pop_access_scope.
	(more_constrained): Normalize before calling out to subsumption. Allow
	classes as arguments.
	(strictly_subsumes): Allow non-templates as arguments. Accept a new
	template argument.
	(weakly_subsumes): New.
	(at_least_as_constrained): Removed.
	(diagnose_other_expression): Removed.
	(diagnose_predicate_constraint): Removed.
	(diagnose_pack_expansion): Removed.
	(diagnose_check_constraint): Removed.
	(diagnose_logical_constraint): Removed.
	(diagnose_expression_constraint): Removed.
	(diagnose_type_constraint): Removed.
	(diagnose_implicit_conversion_constraint): Removed.
	(diagnose_argument_deduction_constraint): Removed.
	(diagnose_exception_constraint): Removed.
	(diagnose_parameterized_constraint): Removed.
	(diagnose_argument_deduction_constraint): Removed.
	(diagnose_argument_deduction_constraint): Removed.
	(diagnose_argument_deduction_constraint): Removed.
	(diagnose_trait_expr): New.
	(diagnose_requires_expr): New.
	(diagnose_atomic_constraint): New.
	(diagnose_valid_expression) Stop wrongly diagnosing valid expressions.
	Don't substitute as if in template decls. This causes substitution
	to generate expressions that aren't suitable for use with the noexcept
	routines.
	(diagnose_valid_type) Likewise.
	(diagnose_compound_requirement) Actually emit diagnostics for
	the causes of errors.Call force_paren_expr_uneval.
	(diagnose_declaration_constraints): Turn on template processing to
	suppress certain analyses.
	* cp-objcp-common.c (cp_common_init_ts): Make concepts typed.
	(cp_get_debug_type): Use hash_map_safe_*.
	* cp-tree.h: New function declarations for semantic actions, other
	facilities. Remove declaration no longer used or needed. Remove
	unused _CONSTR macros.
	(LANG_DECL_HAS_MIN): Add CONCEPT_DECL.
	(template_info_decl_check): Factor macro check into an inline function.
	(DECL_TEMPLATE_INFO): Use new check facility.
	(finish_concept_definition): New. Don't invalid concept declarations
	with invalid initializers.
	(find_template_parameters): New.
	(concept_definition_p): New.
	(concept_check_p): New.
	(variable_concept_check_p): New.
	(force_paren_expr_uneval): New.
	(ovl_iterator::using_p): A USING_DECL by itself was also
	introduced by a using-declaration.
	(struct tree_template_info): Use tree_base instead of
	tree_common. Add tmpl and args fields.
	(TI_TEMPLATE, TI_ARGS): Adjust.
	(DECLTYPE_FOR_INIT_CAPTURE): Remove.
	(CONSTR_CHECK, CONSTR_INFO, CONSTR_EXPR, CONSTR_CONTEXT): New.
	(ATOMIC_CONSTR_MAP, TRAIT_EXPR_LOCATION): New.
	(struct tree_trait_expr): Add locus field.
	(enum tsubst_flags): Add tf_norm as a hint to generate normalization
	context when diagnosing constraint failure.
	* cp-tree.def: Remove unused _CONSTR nodes and rename PRED_CONSTR
	to ATOMIC_CONSTR.
	(CONCEPT_DECL): New.
	* cxx-pretty-print.c: Remove constraint printing code.
	(pp_cxx_concept_definition): New.
	(pp_cxx_template_declaration): Print concept definitions.
	(pp_cxx_check_constraint): Update printing for concept definitions.
	(pp_cxx_nested_name_specifier): Fix a weird
	case where we're printing '::::' for concepts.
	(simple_type_specifier): Print requirements for placeholder types.
	(pp_cxx_constrained_type_spec): Print the associated requirements of
	a placeholder type.
	(pp_cxx_compound_requirement): Add space before the '->'.
	(pp_cxx_parameter_mapping): Print the parameter mapping.
	(pp_cxx_atomic_constraint): Use the function above.
	* decl.c (redeclaration_error_message): New error for concepts.
	(grokdeclarator): Check for and disallow decltype(auto) in parameter
	declarations.
	(grokfndecl): Don't normalize constraints. Add check for constraints
	on declaration.
	(grokvardecl): Don't normalize constraints.
	(grok_special_member_properties): Don't set TYPE_HAS_COMPLEX_*.
	(function_requirements_equivalent_p): New. Compare trailing
	requires clauses. Compare combined constraints in pre-C++20 mode.
	(decls_match): Compare trailing requires clauses. Compare template
	heads for function templates. Remove old constraint comparison.
	Simplify comparison of functions, function templates.
	(duplicate_function_template_decls): New. Refactor a nasty if
	condition into a single predicate.
	(require_deduced_type): Don't complain if we already complained about
	deduction failure.
	(finish_function): Perform auto deduction to ensure that constraints
	are checked even when functions contain no return statements. Only do
	auto deduction if we haven't previously seen any return statements.
	This prevents multiple diagnostics of the same error.
	(store_decomp_type): Remove.
	(cp_finish_decomp): Use hash_map_safe_put.
	* error.c: Remove constraint printing code.
	(dump_decl): Dump concept definitions. Handle wildcard declarations.
	(dump_template_decl): Likewise.
	(dump_type): Print associated requirements for placeholder
	types.
	(rebuild_concept_check): New.
	(maybe_print_single_constraint_context): New.
	(maybe_print_constraint_context): Recursively print nested contexts.
	* init.c (get_nsdmi): Use hash_map_safe_*.
	* lambda.c (maybe_add_lambda_conv_op): Bail if deduction failed.
	(add_capture): Copy parameter packs from init.
	(lambda_capture_field_type): Always use auto for init-capture.
	* logic.cc: Completely rewrite.
	(constraint_hash): New.
	(clause/ctor): Save atoms in the hash table.
	(replace): Save atoms during replacement.
	(insert): Save atoms during insertion.
	(contains): Only search the hash table for containment.
	(clause): Keep a hash of atomic constraints.
	(clause::clause): Explicitly copy the hash table when copying.
	(disjunction_p, conjunction_p, atomic_p, dnf_size, cnf_size): New.
	(diagnose_constraint_size): New.
	(subsumes_constraints_nonnull): Compare the sizes of normalized formula
	to determine the cheapest decomposition.
	* name-lookup.c (diagnose_name_conflict): Diagnose name issues with
	concepts.
	(matching_fn_p): Check constraints.
	(push_class_level_binding_1): Move overloaded functions case down,
	accept FUNCTION_DECL as target_decl.
	* parser.c (enum required_token): New required token for auto.
	(make_location): Add overload taking lexer as last parm.
	(cp_parser_required_error): Diagnose missing auto.
	(cp_parser_diagnose_ungrouped_constraint_plain): New.
	(cp_parser_diagnose_ungrouped_constraint_plain): New.
	(cp_parser_constraint_primary_expression): New. Tentatively parse the
	primary expression. If that fails tentatively parse a lower
	precedence expression in order to diagnose the error.
	(cp_parser_check_non_logical_constraint): New. Performs a trial
	parse of the right-hand-side of non-logical operators in order to
	generate good diagnostics.
	(cp_parser_constraint_logical_and_expression): New.
	(cp_parser_constraint_logical_or_expression): New.
	(cp_parser_requires_clause_expression): New.
	(cp_parser_requires_clause): Renamed to cp_parser_constraint_expression.
	(cp_parser_requires_clause_opt): Parse the requires-clause differently
	in -fconcepts and -std=c++2a modes.
	(cp_parser_requirement_list): Rename to cp_parser_requirement_seq.
	Rewrite so that semicolons are parsed
	along with requirements, not the sequence.
	(cp_parser_simple_requirement): Expect a semicolon at end.
	(cp_parser_compound_requirement): Expect a semicolon at end. Only
	allow trailing-return-type with -fconcepts-ts.
	(cp_parser_nested_requirement): Expect a semicolon at end. Parse
	constraint-expressions.
	(cp_parser_concept_definition): New. Don't fail parsing the concept
	definition if the initializer is ill-formed. Don't declare the concept
	before parsing the initializer.
	(cp_parser_constraint_expression): Declare earlier.
	(cp_parser_type_requirement): Current scope is not valid.
	(cp_parser_requires_expression): Commit to the tentative parse.
	(cp_parser_decl_specifier_seq): Warn when concept appears to be used
	as a decl-specifier.
	(cp_parser_template_declaration_after_parameters): Parse concept
	definitions.
	(cp_parser_template_id): Don't try to resolve a concept template-id yet.
	(cp_parser_template_id_expr): Resolve it as a concept check.
	(cp_parser_decl_specifier_seq): Warn on 'concept bool'.
	(cp_parser_type_parameter): Combine expressions not
	constraints.
	(cp_parser_explicit_template_declaration): Combine expressions not
	constraints.
	(cp_parser_maybe_concept_name): Removed.
	(cp_parser_simple_type_specifier): Handle an error condition of
	a bad constrained type specifier. Expect auto or decltype after
	a concept name. Also handle the case where we have a template-id
	as a concept check.
	(cp_parser_template_introduction): Diagnose errors on invalid
	introductions. Give up if it doesn't start with a concept name.
	Pedwarn if not -fconcepts-ts.
	(synthesize_implicit_template_parm): Don't do consistent binding.
	Use a new flag for constrained parameters. Combine expressions,
	not constraints. Fail if we get a placeholder in block scope.
	Placeholders that do not constrain types are not allowed in parameter
	declarations, so don't handle them.
	(cp_parser_placeholder_type_specifier): New. Implement parsing of
	placeholder type specifiers following a concept name or partial
	concept check. Disallow decltype(auto) parameters.
	(cp_parser_nested_name_specifier_opt): If the token is already
	CPP_NESTED_NAME_SPECIFIER, leave it alone.
	(cp_parser_id_expression, cp_parser_unqualified_id): Call
	cp_parser_template_id_expr.
	(cp_parser_placeholder_type_specifier): Add tentative parm.  Don't
	expect a WILDCARD_DECL.
	(cp_parser_trait_expr): Pass trait_loc down.
	(cp_parser_postfix_expression): Do set location of dependent member
	call.
	* pt.c (finish_concept_definition): New.
	(push_template_decl_real): Handle concept definitions.
	(start_concept_definition): Let push_template_decl_real handle the
	creation of the template.
	(get_constraints): Return null if the table hasn't been initialized.
	(tsubst_copy_and_build): Build template-id expressions for concept
	checks.
	[TRAIT_EXPR]: Pass trait_loc down.
	(lookup_template_class_1): Add the template name to the constraint
	failure diagnostic.
	(lookup_and_finish_template_variable): Build concept checks
	with the correct arguments.
	(tsubst_function_decl): Don't substitute through constraints.
	Always associate constraints with functions.
	(template_parm_level_and_index): Make non-static.
	(for_each_template_parm_r): Handle requires expressions.
	(keep_template_parm): New.
	(find_template_parameters): New.
	(more_specialized_fn): Change how winners and losers are chosen.
	(make_constrained_auto): Don't normalize constraints.
	(template_parameters_equivalent_p): New. Compare template
	parameters. Add a comparison for implicitly vs. explicitly declared
	parameters.
	(template_parameter_lists_equivalent_p): New. Compare template
	parameter lists.
	(template_requirements_equivalent_p): New.
	(template_heads_equivalent_p): New. Compare template heads.
	(template_parameter_constraints_equivalent_p): New.
	(is_compatible_template_arg): Use weakly_subsumes.
	(maybe_new_partial_specialization): Use new constraint comparison
	for finding specializations.
	(process_partial_specialization): Pass main template as argument.
	(more_specialized_partial_spec): Don't immediately return when
	detecting a winner.
	(make_constrained_auto): Handle concept definitions.
	(do_auto_deduction): Update auto deduction for new concept model.
	Extract the function concept correctly; rename constr to check to
	reflect the kind of node.
	(tsubst): Adjust wildcard argument during substitution.
	[DECLTYPE_TYPE]: Remove init-capture handling.
	(tsubst_copy_and_build): Build concept checks, not template ids.
	Defer checks of function concepts. Handle concepts before variable
	templates. Handle calls to function concepts explicitly.
	(coerce_template_parms): Use concept_definition_p. Handle a deduction
	error where a potentially empty pack can be supplied after the last
	parameter of a concept.
	(finish_template_variable): Don't process concepts here.
	(instantiation_dependent_r): Use concept_check_p.
	(tsubst_template_args): Make non-static.
	(make_constrained_placeholder_type): New. Refactored from
	make_constrained_auto.
	(make_constrained_auto) Use make_constrained_placeholder_type.
	(make_constrained_decltype_auto) New.
	(tsubst_function_parms): New.
	(value_dependent_expression_p) [TEMPLATE_ID_EXPR]: Use
	concept_definition_p.
	(push_access_scope, pop_access_scope): No longer static.
	(tsubst_template_parm): Substitute TEMPLATE_PARM_CONSTRAINTS.
	(tsubst_friend_function): Use tsubst_constraint. Use generic_targs_for.
	(get_underlying_template) Use generic_targs_for.
	(uses_parameter_packs): Return tree.
	(gen_elem_of_pack_expansion_instantiation): Don't push
	local_specialization_stack.
	(prepend_one_capture): New.
	(tsubst_lambda_expr): Use prepend_one_capture.	Don't touch
	local_specializations.
	(template_parms_level_to_args): No longer static.
	(add_outermost_template_args): Likewise.
	(find_template_parameter_info): New. Provide context for finding
	template parameters.
	(keep_template_parm): Don't keep parameters declared at depth levels
	greater than those of the template parameters of the source declaration.
	Don't propagate cv-qualified types. Return 0, so we find all template
	parameters, not the just first.
	(any_template_parm_r): New. Handle cases that are mishandled by
	for_each_template_parm_r.
	(generic_targs_for): Factor out of coerce_template_args_for_ttp.
	(tsubst_argument_pack): Factor out of tsubst_template_args.
	(constraint_sat_entry): Removed.
	(constraint_sat_hasher): Removed.
	(concept_spec_entry): Removed.
	(concept_spec_hasher): Removed.
	(constraint_memos): Removed.
	(concept_memos): Removed.
	(lookup_constraint_satisfaction): Removed.
	(memoize_constraint_satisfaction): Removed.
	(lookup_concept_satisfaction): Removed.
	(memoize_concept_satisfaction): Removed.
	(concept_expansions): Removed.
	(get_concept_expansion): Removed.
	(save_concept_expansion): Removed.
	(init_constraint_processing): Remove initialization of non-existing
	resources.
	(find_template_requirement): New. Search for the sub-requirement
	within the associated constraints.
	(convert_generic_types_to_packs): Also transform the associated
	constraint and update the current template requirements.
	(store_defaulted_ttp, lookup_defaulted_ttp): Remove.
	(add_defaults_to_ttp): Use hash_map_safe_*.
	* semantics.c (finish_call_expr): Diagnose calls to concepts.
	Handle concept checks explicitly.
	(finish_id_expression): Evaluate variable concepts as part of
	id-expression processing. Don't treat variable concepts as variables,
	and don't process function concepts as plain id-expressions.
	(force_paren_expr): Add even_uneval parm.
	(finish_trait_expr): Add location parm.
	* tree.c (special_memfn_p): New.
	(cp_expr_location): Handle TRAIT_EXPR.
	* typeck.c (check_return_expr): Actually use the diagnostic kind
	when performing return-type deduction.
	* typeck2.c (build_functional_cast): Don't rely on the location of
	'auto'.
gcc/testsuite/
	* lib/target-supports.exp (check_effective_target_concepts): Check
	for std=c++2a.
gcc/
	* doc/invoke.texi: Document -fconcepts-ts.

From-SVN: r276764