diff --git a/lib/Slic3r/Format/STL.pm b/lib/Slic3r/Format/STL.pm
index 48b242933..26071f384 100644
--- a/lib/Slic3r/Format/STL.pm
+++ b/lib/Slic3r/Format/STL.pm
@@ -13,7 +13,7 @@ sub read_file {
     my ($vertices, $facets) = @{$tmesh->ToPerl};
     
     my $model = Slic3r::Model->new;
-    my $object = $model->add_object(vertices => $vertices);
+    my $object = $model->add_object(vertices => $vertices, mesh_stats => $tmesh->stats);
     my $volume = $object->add_volume(facets => $facets);
     return $model;
 }
diff --git a/lib/Slic3r/GCode.pm b/lib/Slic3r/GCode.pm
index 1f4edde1d..c2db47465 100644
--- a/lib/Slic3r/GCode.pm
+++ b/lib/Slic3r/GCode.pm
@@ -96,9 +96,13 @@ sub change_layer {
     my ($layer) = @_;
     
     $self->layer($layer);
+    
+    # avoid computing overhangs if they're not needed
     $self->_layer_overhangs(
-        $layer->id > 0
+        $layer->id > 0 && ($Slic3r::Config->overhangs || $Slic3r::Config->start_perimeters_at_non_overhang)
             ? [ map $_->expolygon->arrayref, grep $_->surface_type == S_TYPE_BOTTOM, map @{$_->slices}, @{$layer->regions} ]
+        $layer->id > 0 && ($Slic3r::Config->overhangs || $Slic3r::Config->start_perimeters_at_non_overhang)
+            ? [ map $_->expolygon, grep $_->surface_type == S_TYPE_BOTTOM, map @{$_->slices}, @{$layer->regions} ]
             : []
         );
     if ($self->config->avoid_crossing_perimeters) {
@@ -168,8 +172,9 @@ sub extrude_loop {
         @candidates = @concave;
         if (!@candidates) {
             # if none, look for any non-overhang vertex
-            @candidates = grep !Boost::Geometry::Utils::point_covered_by_multi_polygon($_, $self->_layer_overhangs),
-                @{$loop->polygon};
+            if ($Slic3r::Config->start_perimeters_at_non_overhang) {
+                @candidates = grep !Boost::Geometry::Utils::point_covered_by_multi_polygon($_, $self->_layer_overhangs), @{$loop->polygon};
+            }
             if (!@candidates) {
                 # if none, all points are valid candidates
                 @candidates = @{$loop->polygon};
diff --git a/lib/Slic3r/GUI/Plater.pm b/lib/Slic3r/GUI/Plater.pm
index bc521cf1e..8f62008bc 100644
--- a/lib/Slic3r/GUI/Plater.pm
+++ b/lib/Slic3r/GUI/Plater.pm
@@ -317,6 +317,7 @@ sub load_file {
             input_file              => $input_file,
             input_file_object_id    => $i,
             model_object            => $model->objects->[$i],
+            mesh_stats              => $model->objects->[$i]->mesh_stats,  # so that we can free model_object
             instances               => [
                 $model->objects->[$i]->instances
                     ? (map $_->offset, @{$model->objects->[$i]->instances})
@@ -1070,6 +1071,7 @@ sub OnDropFiles {
 package Slic3r::GUI::Plater::Object;
 use Moo;
 
+use List::Util qw(first);
 use Math::ConvexHull::MonotoneChain qw();
 use Slic3r::Geometry qw(X Y Z MIN MAX deg2rad);
 
@@ -1086,6 +1088,7 @@ has 'thumbnail'             => (is => 'rw', trigger => \&_transform_thumbnail);
 has 'transformed_thumbnail' => (is => 'rw');
 has 'thumbnail_scaling_factor' => (is => 'rw', trigger => \&_transform_thumbnail);
 has 'layer_height_ranges'   => (is => 'rw', default => sub { [] }); # [ z_min, z_max, layer_height ]
+has 'mesh_stats'            => (is => 'rw');
 
 # statistics
 has 'facets'                => (is => 'rw');
@@ -1111,7 +1114,18 @@ sub _trigger_model_object {
 sub check_manifoldness {
 	my $self = shift;
 	
-	$self->is_manifold($self->get_model_object->check_manifoldness);
+	if ($self->mesh_stats) {
+	    if (first { $self->mesh_stats->{$_} > 0 } qw(degenerate_facets edges_fixed facets_removed facets_added facets_reversed backwards_edges)) {
+	        warn "Warning: the input file contains manifoldness errors. "
+	            . "Slic3r repaired it successfully by guessing what the correct shape should be, "
+	            . "but you might still want to inspect the G-code before printing.\n";
+	        $self->is_manifold(0);
+	    } else {
+	        $self->is_manifold(1);
+	    }
+	} else {
+    	$self->is_manifold($self->get_model_object->check_manifoldness);
+    }
 	return $self->is_manifold;
 }
 
diff --git a/lib/Slic3r/GUI/Plater/ObjectDialog.pm b/lib/Slic3r/GUI/Plater/ObjectDialog.pm
index 4fc838841..214df0e2c 100644
--- a/lib/Slic3r/GUI/Plater/ObjectDialog.pm
+++ b/lib/Slic3r/GUI/Plater/ObjectDialog.pm
@@ -10,7 +10,7 @@ use base 'Wx::Dialog';
 sub new {
     my $class = shift;
     my ($parent, %params) = @_;
-    my $self = $class->SUPER::new($parent, -1, "Object", wxDefaultPosition, [500,350], wxDEFAULT_DIALOG_STYLE | wxRESIZE_BORDER);
+    my $self = $class->SUPER::new($parent, -1, "Object", wxDefaultPosition, [500,500], wxDEFAULT_DIALOG_STYLE | wxRESIZE_BORDER);
     $self->{object} = $params{object};
     
     $self->{tabpanel} = Wx::Notebook->new($self, -1, wxDefaultPosition, wxDefaultSize, wxNB_TOP | wxTAB_TRAVERSAL);
@@ -50,7 +50,7 @@ sub new {
     my $self = $class->SUPER::new($parent, -1, wxDefaultPosition, wxDefaultSize);
     $self->{object} = $params{object};
     
-    my $grid_sizer = Wx::FlexGridSizer->new(3, 2, 10, 5);
+    my $grid_sizer = Wx::FlexGridSizer->new(3, 2, 5, 5);
     $grid_sizer->SetFlexibleDirection(wxHORIZONTAL);
     $grid_sizer->AddGrowableCol(1);
     
@@ -76,14 +76,34 @@ sub get_properties {
 	my $self = shift;
 	
 	my $object = $self->{object};
-	return [
+	my $properties = [
 		['Name'			=> $object->name],
 		['Size'			=> sprintf "%.2f x %.2f x %.2f", @{$object->transformed_size}],
 		['Facets'		=> $object->facets],
 		['Vertices'		=> $object->vertices],
 		['Materials' 	=> $object->materials],
-		['Two-Manifold' => $object->is_manifold ? 'Yes' : 'No'],
 	];
+	
+	if (my $stats = $object->mesh_stats) {
+	    push @$properties,
+	        [ 'Shells'              => $stats->{number_of_parts} ],
+	        [ 'Volume'              => sprintf('%.2f', $stats->{volume} * ($object->scale**3)) ],
+	        [ 'Degenerate facets'   => $stats->{degenerate_facets} ],
+	        [ 'Edges fixed'         => $stats->{edges_fixed} ],
+	        [ 'Facets removed'      => $stats->{facets_removed} ],
+	        [ 'Facets added'        => $stats->{facets_added} ],
+	        [ 'Facets reversed'     => $stats->{facets_reversed} ],
+	        [ 'Backwards edges'     => $stats->{backwards_edges} ],
+	        # we don't show normals_fixed because we never provide normals
+	        # to admesh, so it generates normals for all facets
+	        ;
+	} else {
+	    push @$properties,
+	        ['Two-Manifold' => $object->is_manifold ? 'Yes' : 'No'],
+	        ;
+	}
+	
+	return $properties;
 }
 
 package Slic3r::GUI::Plater::ObjectDialog::PreviewTab;
diff --git a/lib/Slic3r/Model.pm b/lib/Slic3r/Model.pm
index 71937ef07..ba873da9d 100644
--- a/lib/Slic3r/Model.pm
+++ b/lib/Slic3r/Model.pm
@@ -297,6 +297,7 @@ has 'vertices'  => (is => 'ro', default => sub { [] });
 has 'volumes'   => (is => 'ro', default => sub { [] });
 has 'instances' => (is => 'rw');
 has 'layer_height_ranges' => (is => 'rw', default => sub { [] }); # [ z_min, z_max, layer_height ]
+has 'mesh_stats' => (is => 'rw');
 has '_bounding_box' => (is => 'rw');
 
 sub add_volume {
diff --git a/lib/Slic3r/TriangleMesh.pm b/lib/Slic3r/TriangleMesh.pm
index 8a0ef5706..f97edabbe 100644
--- a/lib/Slic3r/TriangleMesh.pm
+++ b/lib/Slic3r/TriangleMesh.pm
@@ -215,17 +215,34 @@ sub make_loops {
     }
     @lines = grep $_, @lines;
     
+    # build a map of lines by EDGE_A_ID and A_ID
+    my %by_edge_a_id = my %by_a_id = ();
+    for (0..$#lines) {
+        if (defined(my $edge_a_id = $lines[$_][I_EDGE_A_ID])) {
+            $by_edge_a_id{$edge_a_id} //= [];
+            push @{ $by_edge_a_id{$edge_a_id} }, $_;
+        }
+        if (defined(my $a_id = $lines[$_][I_A_ID])) {
+            $by_a_id{$a_id} //= [];
+            push @{ $by_a_id{$a_id} }, $_;
+        }
+    }
+    
     my (@polygons, @failed_loops) = ();
-    CYCLE: while (@lines) {
+    my %used_lines = ();
+    CYCLE: while (1) {
         # take first spare line and start a new loop
-        my @loop = (shift @lines);
+        my $first_idx = first { !exists $used_lines{$_} } 0..$#lines;
+        last if !defined $first_idx;
+        $used_lines{$first_idx} = 1;
+        my @loop = ($lines[$first_idx]);
         
         while (1) {
             # find a line starting where last one finishes
             my $line_idx;
-            $line_idx = first { defined $lines[$_][I_EDGE_A_ID] && $lines[$_][I_EDGE_A_ID] == $loop[-1][I_EDGE_B_ID] } 0..$#lines
+            $line_idx = first { !exists $used_lines{$_} } @{ $by_edge_a_id{$loop[-1][I_EDGE_B_ID]} // [] }
                 if defined $loop[-1][I_EDGE_B_ID];
-            $line_idx ||= first { defined $lines[$_][I_A_ID] && $lines[$_][I_A_ID] == $loop[-1][I_B_ID] } 0..$#lines
+            $line_idx //= first { !exists $used_lines{$_} } @{ $by_a_id{$loop[-1][I_B_ID]} // [] }
                 if defined $loop[-1][I_B_ID];
             
             if (!defined $line_idx) {
@@ -244,7 +261,8 @@ sub make_loops {
                 push @failed_loops, [@loop];
                 next CYCLE;
             }
-            push @loop, splice @lines, $line_idx, 1;
+            push @loop, $lines[$line_idx];
+            $used_lines{$line_idx} = 1;
         }
     }
     
diff --git a/xs/src/ExPolygon.hpp b/xs/src/ExPolygon.hpp
index c8ebcd84f..7363a6a73 100644
--- a/xs/src/ExPolygon.hpp
+++ b/xs/src/ExPolygon.hpp
@@ -10,6 +10,8 @@ extern "C" {
 
 #include "Point.hpp"
 
+namespace Slic3r {
+
 typedef std::vector<Point> Polygon;
 typedef std::vector<Polygon> Polygons;
 
@@ -98,4 +100,6 @@ polygon2perl(Polygon& poly) {
     return sv_bless(newRV_noinc((SV*)av), gv_stashpv("Slic3r::Polygon", GV_ADD));
 }
 
+}
+
 #endif
diff --git a/xs/src/Point.hpp b/xs/src/Point.hpp
index 6b5ea3b06..c640e207a 100644
--- a/xs/src/Point.hpp
+++ b/xs/src/Point.hpp
@@ -10,6 +10,8 @@ extern "C" {
 
 #include <math.h>
 
+namespace Slic3r {
+
 class Point
 {
     public:
@@ -36,4 +38,6 @@ point2perl(Point& point) {
     return sv_bless(newRV_noinc((SV*)av), gv_stashpv("Slic3r::Point", GV_ADD));
 }
 
+}
+
 #endif
diff --git a/xs/src/TriangleMesh.cpp b/xs/src/TriangleMesh.cpp
index 462a93347..901bdfa47 100644
--- a/xs/src/TriangleMesh.cpp
+++ b/xs/src/TriangleMesh.cpp
@@ -1,5 +1,7 @@
 #include "TriangleMesh.hpp"
 
+namespace Slic3r {
+
 TriangleMesh::TriangleMesh() {}
 TriangleMesh::~TriangleMesh() {
     stl_close(&stl);
@@ -86,6 +88,12 @@ TriangleMesh::Repair() {
     
     // normal_values
     stl_fix_normal_values(&stl);
+    
+    // always calculate the volume and reverse all normals if volume is negative
+    stl_calculate_volume(&stl);
+    
+    // neighbors
+    stl_verify_neighbors(&stl);
 }
 
 void
@@ -130,3 +138,5 @@ TriangleMesh::ToPerl() {
     av_store(result, 1, newRV_noinc((SV*)facets));
     return result;
 }
+
+}
diff --git a/xs/src/TriangleMesh.hpp b/xs/src/TriangleMesh.hpp
index 56380ebf8..ec0869117 100644
--- a/xs/src/TriangleMesh.hpp
+++ b/xs/src/TriangleMesh.hpp
@@ -10,6 +10,8 @@ extern "C" {
 #include "ppport.h"
 }
 
+namespace Slic3r {
+
 class TriangleMesh
 {
     public:
@@ -20,8 +22,9 @@ class TriangleMesh
     void Repair();
     void WriteOBJFile(char* output_file);
     AV* ToPerl();
-    private:
     stl_file stl;
 };
 
+}
+
 #endif
diff --git a/xs/src/ZTable.hpp b/xs/src/ZTable.hpp
index 045722eec..fcdf553fe 100644
--- a/xs/src/ZTable.hpp
+++ b/xs/src/ZTable.hpp
@@ -8,6 +8,8 @@ extern "C" {
 #include "ppport.h"
 }
 
+namespace Slic3r {
+
 class ZTable
 {
     public:
@@ -21,4 +23,6 @@ ZTable::ZTable(std::vector<unsigned int>* ztable) :
 {
 }
 
+}
+
 #endif
diff --git a/xs/src/myinit.h b/xs/src/myinit.h
index 4f534519c..633fe7583 100644
--- a/xs/src/myinit.h
+++ b/xs/src/myinit.h
@@ -3,6 +3,9 @@
 
 #include <vector>
 
+namespace Slic3r {}
+using namespace Slic3r;
+
 #define av_store_point_xy(AV, X, Y)              \
   av_store(AV, 0, newSViv(X));                   \
   av_store(AV, 1, newSViv(Y))
diff --git a/xs/t/01_trianglemesh.t b/xs/t/01_trianglemesh.t
index 8d3c5dd0d..42ed11145 100644
--- a/xs/t/01_trianglemesh.t
+++ b/xs/t/01_trianglemesh.t
@@ -4,7 +4,7 @@ use strict;
 use warnings;
 
 use Slic3r::XS;
-use Test::More tests => 3;
+use Test::More tests => 5;
 
 is Slic3r::TriangleMesh::XS::hello_world(), 'Hello world!',
     'hello world';
@@ -21,6 +21,10 @@ my $cube = {
     my ($vertices, $facets) = @{$m->ToPerl};
     is_deeply $vertices, $cube->{vertices}, 'vertices arrayref roundtrip';
     is_deeply $facets, $cube->{facets}, 'facets arrayref roundtrip';
+    
+    my $stats = $m->stats;
+    is $stats->{number_of_facets}, scalar(@{ $cube->{facets} }), 'stats.number_of_facets';
+    ok abs($stats->{volume} - 20*20*20) < 1E-3, 'stats.volume';
 }
 
 __END__
diff --git a/xs/xsp/TriangleMesh.xsp b/xs/xsp/TriangleMesh.xsp
index 6952dfdbd..cf4ae8d64 100644
--- a/xs/xsp/TriangleMesh.xsp
+++ b/xs/xsp/TriangleMesh.xsp
@@ -13,6 +13,27 @@
     void Repair();
     void WriteOBJFile(char* output_file);
     AV* ToPerl();
+%{
+
+SV*
+TriangleMesh::stats()
+    CODE:
+        HV* hv = newHV();
+        (void)hv_stores( hv, "number_of_facets",    newSViv(THIS->stl.stats.number_of_facets) );
+        (void)hv_stores( hv, "number_of_parts",     newSViv(THIS->stl.stats.number_of_parts) );
+        (void)hv_stores( hv, "volume",              newSVnv(THIS->stl.stats.volume) );
+        (void)hv_stores( hv, "degenerate_facets",   newSViv(THIS->stl.stats.degenerate_facets) );
+        (void)hv_stores( hv, "edges_fixed",         newSViv(THIS->stl.stats.edges_fixed) );
+        (void)hv_stores( hv, "facets_removed",      newSViv(THIS->stl.stats.facets_removed) );
+        (void)hv_stores( hv, "facets_added",        newSViv(THIS->stl.stats.facets_added) );
+        (void)hv_stores( hv, "facets_reversed",     newSViv(THIS->stl.stats.facets_reversed) );
+        (void)hv_stores( hv, "backwards_edges",     newSViv(THIS->stl.stats.backwards_edges) );
+        (void)hv_stores( hv, "normals_fixed",       newSViv(THIS->stl.stats.normals_fixed) );
+        RETVAL = (SV*)newRV_noinc((SV*)hv);
+    OUTPUT:
+        RETVAL
+
+%}
 };
 
 %package{Slic3r::TriangleMesh::XS};