Creating a Failure is now more efficient

src/core/Failure.pm

@@ -8,28 +8,27 @@ my class Failure is Nil {
     has Int $!handled;   # alas, native int breaks on the JVM
 #?endif
 
+    method !SET-SELF($!exception) {
+        $!backtrace = $!exception.backtrace || Backtrace.new(5);
+        $!exception.reset-backtrace;
+        self
+    }
+
     multi method new() {
         my $stash := CALLER::;
         my $payload = $stash<$!>.DEFINITE ?? $stash<$!> !! "Failed";
-        self.bless(:exception( $payload ~~ Exception
-          ?? $payload !! X::AdHoc.new(:$payload)
-        ))
+        nqp::create(self)!SET-SELF(
+          $payload ~~ Exception ?? $payload !! X::AdHoc.new(:$payload)
+        )
     }
-    multi method new(Exception $exception) {
-        self.bless(:$exception);
+    multi method new(Exception:D \exception) {
+        nqp::create(self)!SET-SELF(exception)
     }
     multi method new($payload) {
-        self.bless(:exception( $payload ~~ Exception
-          ?? $payload !! X::AdHoc.new(:$payload)
-        ))
+        nqp::create(self)!SET-SELF(X::AdHoc.new(:$payload))
     }
     multi method new(|cap (*@msg)) {
-         self.bless(:exception(X::AdHoc.from-slurpy(|cap)));
-    }
-
-    submethod BUILD(:$!exception --> Nil) {
-        $!backtrace = $!exception.backtrace() || Backtrace.new(8);
-        $!exception.reset-backtrace;
+        nqp::create(self)!SET-SELF(X::AdHoc.from-slurpy(|cap))
     }
 
     # "Shouldn't happen."  We use note here because the dynamic scope in GC is likely meaningless.