Fix reproducible build issue caused by changing memory addresses of l…

…abels

When a QASTCompilerInstance is somehow referenced (directly or indirectly) by
compiled bytecode, this pulls in references to frames and thus the frames'
%!labels lookup hash which was keyed on the nqp::objectid of those labels.
Since nqp::objectid uses memory addresses and those may change from run to
run, this could lead to differences in build results. Use an incremented id
counter instead, just like we do for QAST::Block's cuids.

lib/MAST/Nodes.nqp

@@ -410,12 +410,29 @@ module Arg {
 # Labels (used directly in the instruction stream indicates where the
 # label goes; can also be used as an instruction operand).
 class MAST::Label is MAST::Node {
+    my int $cur_id := 0;
+    my $cur_id_lock := NQPLock.new;
+    has $!id;
     method new() {
         my $label := nqp::create(self);
+
+        nqp::lock($cur_id_lock);
+        $cur_id := $cur_id + 1;
+        nqp::unlock($cur_id_lock);
+        $label.set-id(~$cur_id);
+
         $*MAST_FRAME.keep-label($label);
         $label
     }
 
+    method set-id($id) {
+        $!id := $id;
+    }
+
+    method id() {
+        $!id
+    }
+
     method dump_lines(@lines, $indent) {
         my int $addr := nqp::where(self);
         nqp::push(@lines, $indent ~ "MAST::Label <$addr>");
@@ -1139,7 +1156,7 @@ class MAST::Frame is MAST::Node {
     method labels() { %!labels }
     method label-fixups() { %!label-fixups }
     method resolve-label($label) {
-        %!labels{nqp::objectid($label)}
+        %!labels{$label.id}
     }
 
     method keep-label(MAST::Label $l) {
@@ -1148,7 +1165,7 @@ class MAST::Frame is MAST::Node {
 
     method add-label(MAST::Label $i) {
         my int $pos := nqp::elems($!bytecode);
-        my str $key := nqp::objectid($i);
+        my str $key := $i.id;
         if %!labels{$key} {
             nqp::die("Duplicate label at $pos");
         }
@@ -1172,7 +1189,7 @@ class MAST::Frame is MAST::Node {
         $Arg::obj   # $MVM_reg_obj             := 8;
     ];
     method compile_label($bytecode, $arg) {
-        my $key := nqp::objectid($arg);
+        my $key := $arg.id;
         my %labels := self.labels;
         nqp::push_i(@!child-label-fixups, nqp::elems($!bytecode));
         if nqp::existskey(%labels, $key) {