2015-05-07 Andrew Sutton <andrew.n.sutton@gmail.com>

2015-05-07  Andrew Sutton  <andrew.n.sutton@gmail.com>

	Implement argument deduction constraints.
	* gcc/cp/cp-tree.def (DEDUCT_CONSTR): Add a third operand.
	* gcc/cp/cp-tree.h (auto_deduction_context): New. Flags to control
	diagnostics in auto deduction.
	(do_auto_deduction): New overload to allow for control of diagnostics.
	(tsubst_constraint): Make extern.
	* gcc/cp/pt.c (tsubst): Propagate constraints for place holders.
	(do_auto_deduction): New overload that calls the expanded version
	with default args.
	(do_auto_deduction): Control diagnostics with tf_subst_flags and
	auto_deduction_context.
	(do_auto_deduction): Only check constraints for when not using
	decltype(auto).
	* gcc/cp/constraint.cc (xform_compound_requirement): Build argument
	deduction constraints.
	(xform_atomic): Don't check the types of dependent expressions,
	even when not processing templates.
	(satisfy_argument_deduction_constraint): Implement this.
	* gcc/testsuite/g++.dg/concepts/placeholder1.C: Add tests for
	more complex failures.
	* gcc/testsuite/g++.dg/concepts/placeholder2.C: New.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/branches/c++-concepts@222891 138bc75d-0d04-0410-961f-82ee72b054a4