Optimise S_mro_get_linear_isa_dfs() when dealing with the first parent class.

Benchmarking with single inheritance suggests that this is 10% faster.

1 files changed, 53 insertions, 0 deletions

diff --git a/t/mro/isa_dfs.t b/t/mro/isa_dfs.t
new file mode 100644
index 0000000000..6eabf1f27d
--- /dev/null
+++ b/t/mro/isa_dfs.t
@@ -0,0 +1,53 @@
+#!perl -w
+
+BEGIN {
+    chdir 't' if -d 't';
+    @INC = '../lib';
+    require "./test.pl";
+}
+
+use strict;
+
+plan 'no_plan';
+
+# package klonk doesn't have a stash.
+
+package kapow;
+
+# No parents
+
+package urkkk;
+
+# 1 parent
+@urkkk::ISA = 'klonk';
+
+package kayo;
+
+# 2 parents
+@urkkk::ISA = ('klonk', 'kapow');
+
+package thwacke;
+
+# No parents, has @ISA
+@thwacke::ISA = ();
+
+package zzzzzwap;
+
+@zzzzzwap::ISA = ('thwacke', 'kapow');
+
+package whamm;
+
+@whamm::ISA = ('kapow', 'thwacke');
+
+package main;
+
+require mro;
+
+foreach my $package (qw(klonk urkkk kapow kayo thwacke zzzzzwap whamm)) {
+    my $ref = bless [], $package;
+    my $isa = mro::get_linear_isa($package);
+
+    foreach my $class ($package, @$isa, 'UNIVERSAL') {
+	isa_ok($ref, $class, $package);
+    }
+}