Check proto as well as candidates in optimizer.

This fixes issues where we could end up inlining calls to candidates
that would never be reachable due to restrictions in the proto. Also,
we catch some such issues at compile time now.

src/Perl6/Optimizer.pm

@@ -163,34 +163,36 @@ class Perl6::Optimizer {
                 # the proto.
                 my $dispatcher;
                 try { if $obj.is_dispatcher { $dispatcher := 1 } }
-                if $dispatcher {
-                    # Try to do compile-time multi-dispatch.
+                if $dispatcher && $obj.onlystar {
+                    # Try to do compile-time multi-dispatch. Need to consider
+                    # both the proto and the multi candidates.
                     my @ct_arg_info := self.analyze_args_for_ct_call($op);
                     if +@ct_arg_info {
                         my @types := @ct_arg_info[0];
                         my @flags := @ct_arg_info[1];
-                        my @ct_result := pir::perl6_multi_dispatch_ct__PPPP($obj, @types, @flags);
-                        if @ct_result[0] == 1 {
-                            my $chosen := @ct_result[1];
+                        my $ct_result_proto := pir::perl6_trial_bind_ct__IPPP($obj.signature, @types, @flags);
+                        my @ct_result_multi := pir::perl6_multi_dispatch_ct__PPPP($obj, @types, @flags);
+                        if $ct_result_proto == 1 && @ct_result_multi[0] == 1 {
+                            my $chosen := @ct_result_multi[1];
                             if $op.op eq 'chain' { $!chain_depth := $!chain_depth - 1 }
-                            if $*LEVEL >= 2 && $obj.onlystar {
+                            if $*LEVEL >= 2 {
                                 return nqp::can($chosen, 'inline_info') && nqp::istype($chosen.inline_info, QAST::Node)
                                     ?? self.inline_call($op, $chosen)
                                     !! self.call_ct_chosen_multi($op, $obj, $chosen);
                             }
                         }
-                        elsif @ct_result[0] == -1 {
+                        elsif $ct_result_proto == -1 || @ct_result_multi[0] == -1 {
                             self.report_innevitable_dispatch_failure($op, @types, @flags, $obj);
                         }
                     }
 
                     # Otherwise, inline the proto.
                     if $op.op eq 'chain' { $!chain_depth := $!chain_depth - 1 }
-                    if $*LEVEL >= 2 && $obj.onlystar {
+                    if $*LEVEL >= 2 {
                         return self.inline_proto($op, $obj);
                     }
                 }
-                elsif nqp::can($obj, 'signature') {
+                elsif !$dispatcher && nqp::can($obj, 'signature') {
                     # If we know enough about the arguments, do a "trial bind".
                     my @ct_arg_info := self.analyze_args_for_ct_call($op);
                     if +@ct_arg_info {