config: config_fh_parse: micro-optimize

We can avoid a slow regexp capture and instead and rely on
rindex + substr to extract the section from the config file.

Then we use the defined-or-assignment (//=) operator combined
with the documented return value of `push' to ensure @section_order
is unique without repeating a hash lookup.

Finally, we avoid short-lived variables inside the loop and
declare them subroutine-wide to knock a teeny bit of allocation
time.

Combined, these optimizations bring the ~1.22s
PublicInbox::Config->new time down to ~0.98s with 50K inboxes.

1 files changed, 6 insertions, 11 deletions

diff --git a/lib/PublicInbox/Config.pm b/lib/PublicInbox/Config.pm
index 4d143c6e..60107d45 100644
--- a/lib/PublicInbox/Config.pm
+++ b/lib/PublicInbox/Config.pm
@@ -132,20 +132,15 @@ sub default_file {
 
 sub config_fh_parse ($$$) {
         my ($fh, $rs, $fs) = @_;
-        my %rv;
-        my (%section_seen, @section_order);
+        my (%rv, %section_seen, @section_order, $line, $k, $v, $section, $cur);
         local $/ = $rs;
-        while (defined(my $line = <$fh>)) {
+        while (defined($line = <$fh>)) { # performance critical with giant configs
                 chomp $line;
-                my ($k, $v) = split($fs, $line, 2);
-                my ($section) = ($k =~ /\A(\S+)\.[^\.]+\z/);
-                unless (defined $section_seen{$section}) {
-                        $section_seen{$section} = 1;
-                        push @section_order, $section;
-                }
+                ($k, $v) = split($fs, $line, 2);
+                $section = substr($k, 0, rindex($k, '.'));
+                $section_seen{$section} //= push(@section_order, $section);
 
-                my $cur = $rv{$k};
-                if (defined $cur) {
+                if (defined($cur = $rv{$k})) {
                         if (ref($cur) eq "ARRAY") {
                                 push @$cur, $v;
                         } else {