optimization: pagespec_match_list with no num limit matches before sorting

This can be a lot faster, since huge numbers of pages are not sorted
only to mostly be thrown away. It sped up a build of my blog by at least
5 minutes.

IkiWiki.pm

@@ -1951,8 +1951,9 @@ sub add_link ($$;$) {
 	}
 }
 
-sub sortspec_translate ($) {
+sub sortspec_translate ($$) {
 	my $spec = shift;
+	my $reverse = shift;
 
 	my $code = "";
 	my @data;
@@ -2007,6 +2008,10 @@ sub sortspec_translate ($) {
 		return sub { 0 };
 	}
 
+	if ($reverse) {
+		$code="-($code)";
+	}
+
 	no warnings;
 	return eval 'sub { '.$code.' }';
 }
@@ -2109,18 +2114,20 @@ sub pagespec_match_list ($$;@) {
 			? grep { ! $params{filter}->($_) } keys %pagesources
 			: keys %pagesources;
 	}
-
-	if (defined $params{sort}) {
-		@candidates = IkiWiki::SortSpec::sort_pages($params{sort},
-			@candidates);
+	
+	my $num=$params{num};
+	my $sort=$params{sort};
+	my $reverse=$params{reverse};
+	# when only the top matches will be returned, it's efficient to
+	# sort before matching to pagespec,
+	if (defined $num && defined $sort) {
+		@candidates=IkiWiki::SortSpec::sort_pages(
+			$sort, $reverse, @candidates);
 	}
-
-	@candidates=reverse(@candidates) if $params{reverse};
 	
 	$depends{$page}{$pagespec} |= ($params{deptype} || $DEPEND_CONTENT);
 	
 	# clear params, remainder is passed to pagespec
-	my $num=$params{num};
 	delete @params{qw{num deptype reverse sort filter list}};
 	
 	my @matches;
@@ -2144,7 +2151,15 @@ sub pagespec_match_list ($$;@) {
 		$depends_simple{$page}{lc $k} |= $i->{$k};
 	}
 
-	return @matches;
+	# when all matches will be returned, it's efficient to
+	# sort after matching
+	if (! defined $num && defined $sort) {
+		return IkiWiki::SortSpec::sort_pages(
+			$sort, $reverse, @matches);
+	}
+	else {
+		return @matches;
+	}
 }
 
 sub pagespec_valid ($) {
@@ -2437,9 +2452,8 @@ package IkiWiki::SortSpec;
 # This is in the SortSpec namespace so that the $a and $b that sort() uses
 # are easily available in this namespace, for cmp functions to use them.
 sub sort_pages {
-	my $f = IkiWiki::sortspec_translate(shift);
-
-	return sort $f @_;
+	my $f=IkiWiki::sortspec_translate(shift, shift);
+	sort $f @_
 }
 
 sub cmp_title {

doc/todo/smarter_sorting.mdwn

@@ -29,5 +29,8 @@ date range.) Well, in this case, it *does* make sense to flip it, limit by
 pagespe first, and do a (quick)sort second. (No influence complications,
 either.)
 
+> Flipping when there's no limit implemented, and it knocked 1/3 off
+> the rebuild time of my blog's archive pages. --[[Joey]] 
+
 Adding these special cases will be more complicated, but I think the best
 of both worlds. --[[Joey]]

t/pagespec_match_list.t

@@ -1,7 +1,7 @@
 #!/usr/bin/perl
 use warnings;
 use strict;
-use Test::More tests => 90;
+use Test::More tests => 92;
 
 BEGIN { use_ok("IkiWiki"); }
 
@@ -38,12 +38,16 @@ $links{foo3}=[qw{bar}];
 is_deeply([pagespec_match_list("foo", "bar")], ["bar"]);
 is_deeply([sort(pagespec_match_list("foo", "* and !post/*"))], ["bar", "foo", "foo2", "foo3"]);
 is_deeply([sort(pagespec_match_list("foo", "post/*"))], ["post/1", "post/2", "post/3"]);
+is_deeply([pagespec_match_list("foo", "post/*", sort => "title")],
+	["post/1", "post/2", "post/3"]);
 is_deeply([pagespec_match_list("foo", "post/*", sort => "title", reverse => 1)],
 	["post/3", "post/2", "post/1"]);
 is_deeply([pagespec_match_list("foo", "post/*", sort => "title", num => 2)],
 	["post/1", "post/2"]);
 is_deeply([pagespec_match_list("foo", "post/*", sort => "title", num => 50)],
 	["post/1", "post/2", "post/3"]);
+is_deeply([pagespec_match_list("foo", "post/*", sort => "title", num => 50, reverse => 1)],
+	["post/3", "post/2", "post/1"]);
 is_deeply([pagespec_match_list("foo", "post/*", sort => "title",
                          filter => sub { $_[0] =~ /3/}) ],
 	["post/1", "post/2"]);