Use the constant _CAN_PCS to optimise out things that can't happen pre 5.10

diff --git a/lib/constant.pm b/lib/constant.pm
index 24a6603..a51ee7f 100644 (file)
--- a/lib/constant.pm
+++ b/lib/constant.pm
@@ -117,7 +117,9 @@ sub import {
            $declared{$full_name}++;
            if ($multiple || @_ == 1) {
                my $scalar = $multiple ? $constants->{$name} : $_[0];
-               if ($symtab && !exists $symtab->{$name}) {
+               # The constant serves to optimise this entire block out on
+               # 5.8 and earlier.
+               if (_CAN_PCS && $symtab && !exists $symtab->{$name}) {
                    # No typeglob yet, so we can use a reference as space-
                    # efficient proxy for a constant subroutine
                    # The check in Perl_ck_rvconst knows that inlinable
@@ -137,7 +139,7 @@ sub import {
        }
     }
     # Flush the cache exactly once if we make any direct symbol table changes.
-    mro::method_changed_in($pkg) if $flush_mro;
+    mro::method_changed_in($pkg) if _CAN_PCS && $flush_mro;
 }
 
 1;