diff --git a/CMakeLists.txt b/CMakeLists.txt
index f60c8bde6..ba291e450 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -162,15 +162,15 @@ if (CMAKE_COMPILER_IS_GNUCC OR CMAKE_COMPILER_IS_GNUXX)
     endif ()
 endif()
 
-if ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU" OR "${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang")
-    add_compile_options(-Wall)
+if ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU" OR "${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang")
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall" )
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-reorder" )
 
     # On GCC and Clang, no return from a non-void function is a warning only. Here, we make it an error.
     add_compile_options(-Werror=return-type)
 
     #removes LOTS of extraneous Eigen warnings (GCC only supports it since 6.1)
-    #if("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang" OR CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 6.1)
+    #if("${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang" OR CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 6.1)
         # add_compile_options(-Wno-ignored-attributes) # Tamas: Eigen include dirs are marked as SYSTEM
     #endif()
 
diff --git a/src/libslic3r/GCode/WipeTower.cpp b/src/libslic3r/GCode/WipeTower.cpp
index 354ec6d9e..55a6c4437 100644
--- a/src/libslic3r/GCode/WipeTower.cpp
+++ b/src/libslic3r/GCode/WipeTower.cpp
@@ -157,7 +157,7 @@ public:
             change_analyzer_mm3_per_mm(len, e);
 			// Width of a squished extrusion, corrected for the roundings of the squished extrusions.
 			// This is left zero if it is a travel move.
-			float width = float(double(e) * /*Filament_Area*/2.40528 / (len * m_layer_height));
+			float width = float(double(e) * m_filpar[0].filament_area / (len * m_layer_height));
 			// Correct for the roundings of a squished extrusion.
 			width += m_layer_height * float(1. - M_PI / 4.);
 			if (m_extrusions.empty() || m_extrusions.back().pos != rotated_current_pos)
@@ -822,7 +822,7 @@ void WipeTower::toolchange_Unload(
     while (i < m_filpar[m_current_tool].ramming_speed.size())
     {
         const float x = volume_to_length(m_filpar[m_current_tool].ramming_speed[i] * 0.25f, line_width, m_layer_height);
-        const float e = m_filpar[m_current_tool].ramming_speed[i] * 0.25f / Filament_Area; // transform volume per sec to E move;
+        const float e = m_filpar[m_current_tool].ramming_speed[i] * 0.25f / filament_area(); // transform volume per sec to E move;
         const float dist = std::min(x - e_done, remaining);		  // distance to travel for either the next 0.25s, or to the next turnaround
         const float actual_time = dist/x * 0.25;
         writer.ram(writer.x(), writer.x() + (m_left_to_right ? 1.f : -1.f) * dist, 0, 0, e * (dist / x), dist / (actual_time / 60.));
diff --git a/src/libslic3r/GCode/WipeTower.hpp b/src/libslic3r/GCode/WipeTower.hpp
index badb3e8b2..6dfad1b8c 100644
--- a/src/libslic3r/GCode/WipeTower.hpp
+++ b/src/libslic3r/GCode/WipeTower.hpp
@@ -111,7 +111,8 @@ public:
 	// Set the extruder properties.
 	void set_extruder(size_t idx, std::string material, int temp, int first_layer_temp, float loading_speed, float loading_speed_start,
                       float unloading_speed, float unloading_speed_start, float delay, int cooling_moves,
-                      float cooling_initial_speed, float cooling_final_speed, std::string ramming_parameters, float max_volumetric_speed, float nozzle_diameter)
+                      float cooling_initial_speed, float cooling_final_speed, std::string ramming_parameters, float max_volumetric_speed,
+                      float nozzle_diameter, float filament_diameter)
 	{
         //while (m_filpar.size() < idx+1)   // makes sure the required element is in the vector
         m_filpar.push_back(FilamentParameters());
@@ -133,10 +134,12 @@ public:
             m_filpar[idx].cooling_final_speed     = cooling_final_speed;
         }
 
-        if (max_volumetric_speed != 0.f)
-            m_filpar[idx].max_e_speed = (max_volumetric_speed / Filament_Area);
+        m_filpar[idx].filament_area = (M_PI/4.f) * pow(filament_diameter, 2); // all extruders are assumed to have the same filament diameter at this point
         m_filpar[idx].nozzle_diameter = nozzle_diameter; // to be used in future with (non-single) multiextruder MM
 
+        if (max_volumetric_speed != 0.f)
+            m_filpar[idx].max_e_speed = (max_volumetric_speed / filament_area());
+
         m_perimeter_width = nozzle_diameter * Width_To_Nozzle_Ratio; // all extruders are now assumed to have the same diameter
 
         if (m_semm) {
@@ -248,6 +251,7 @@ public:
         float               max_e_speed = std::numeric_limits<float>::max();
         std::vector<float>  ramming_speed;
         float               nozzle_diameter;
+        float               filament_area;
     };
 
 private:
@@ -261,9 +265,11 @@ private:
 
 
     const bool  m_peters_wipe_tower   = false; // sparse wipe tower inspired by Peter's post processor - not finished yet
-    const float Filament_Area         = float(M_PI * 1.75f * 1.75f / 4.f); // filament area in mm^2
     const float Width_To_Nozzle_Ratio = 1.25f; // desired line width (oval) in multiples of nozzle diameter - may not be actually neccessary to adjust
     const float WT_EPSILON            = 1e-3f;
+    const float filament_area() const {
+        return m_filpar[0].filament_area; // all extruders are assumed to have the same filament diameter at this point
+    }
 
 
 	bool   m_semm               = true; // Are we using a single extruder multimaterial printer?
@@ -315,7 +321,7 @@ private:
 	{
 		if ( layer_height < 0 )
 			return m_extrusion_flow;
-		return layer_height * ( m_perimeter_width - layer_height * (1.f-float(M_PI)/4.f)) / Filament_Area;
+		return layer_height * ( m_perimeter_width - layer_height * (1.f-float(M_PI)/4.f)) / filament_area();
 	}
 
 	// Calculates length of extrusion line to extrude given volume
diff --git a/src/libslic3r/Print.cpp b/src/libslic3r/Print.cpp
index a9b8a827f..5702f49e3 100644
--- a/src/libslic3r/Print.cpp
+++ b/src/libslic3r/Print.cpp
@@ -1092,6 +1092,13 @@ std::string Print::validate() const
     }
 
     if (this->has_wipe_tower() && ! m_objects.empty()) {
+        // make sure all extruders use same diameter filament and have the same nozzle diameter
+        for (const auto& extruder_idx : extruders()) {
+            if (m_config.nozzle_diameter.get_at(extruder_idx) != m_config.nozzle_diameter.get_at(extruders().front())
+             || m_config.filament_diameter.get_at(extruder_idx) != m_config.filament_diameter.get_at(extruders().front()))
+                 return L("The wipe tower is only supported if all extruders have the same nozzle diameter and use filaments of the same diameter.");
+        }
+
         if (m_config.gcode_flavor != gcfRepRap && m_config.gcode_flavor != gcfRepetier && m_config.gcode_flavor != gcfMarlin)
             return L("The Wipe Tower is currently only supported for the Marlin, RepRap/Sprinter and Repetier G-code flavors.");
         if (! m_config.use_relative_e_distances)
@@ -1701,7 +1708,8 @@ void Print::_make_wipe_tower()
 			(float)m_config.filament_cooling_final_speed.get_at(i),
             m_config.filament_ramming_parameters.get_at(i),
             m_config.filament_max_volumetric_speed.get_at(i),
-            m_config.nozzle_diameter.get_at(i));
+            m_config.nozzle_diameter.get_at(i),
+            m_config.filament_diameter.get_at(i));
 
     m_wipe_tower_data.priming = Slic3r::make_unique<std::vector<WipeTower::ToolChangeResult>>(
         wipe_tower.prime((float)this->skirt_first_layer_height(), m_wipe_tower_data.tool_ordering.all_extruders(), false));
diff --git a/src/libslic3r/Utils.hpp b/src/libslic3r/Utils.hpp
index 09e24a475..8a4f1424b 100644
--- a/src/libslic3r/Utils.hpp
+++ b/src/libslic3r/Utils.hpp
@@ -172,7 +172,7 @@ extern std::string xml_escape(std::string text);
 #if defined __GNUC__ && __GNUC__ < 5 && !defined __clang__
 // Older GCCs don't have std::is_trivially_copyable
 // cf. https://gcc.gnu.org/onlinedocs/gcc-4.9.4/libstdc++/manual/manual/status.html#status.iso.2011
-#warning "GCC version < 5, faking std::is_trivially_copyable"
+// #warning "GCC version < 5, faking std::is_trivially_copyable"
 template<typename T> struct IsTriviallyCopyable { static constexpr bool value = true; };
 #else
 template<typename T> struct IsTriviallyCopyable : public std::is_trivially_copyable<T> {};
diff --git a/src/slic3r/GUI/Gizmos/GLGizmoBase.cpp b/src/slic3r/GUI/Gizmos/GLGizmoBase.cpp
index 4b975e87e..a65074646 100644
--- a/src/slic3r/GUI/Gizmos/GLGizmoBase.cpp
+++ b/src/slic3r/GUI/Gizmos/GLGizmoBase.cpp
@@ -166,7 +166,7 @@ void GLGizmoBase::set_highlight_color(const float* color)
 
 void GLGizmoBase::enable_grabber(unsigned int id)
 {
-    if ((0 <= id) && (id < (unsigned int)m_grabbers.size()))
+    if (id < m_grabbers.size())
         m_grabbers[id].enabled = true;
 
     on_enable_grabber(id);
@@ -174,7 +174,7 @@ void GLGizmoBase::enable_grabber(unsigned int id)
 
 void GLGizmoBase::disable_grabber(unsigned int id)
 {
-    if ((0 <= id) && (id < (unsigned int)m_grabbers.size()))
+    if (id < m_grabbers.size())
         m_grabbers[id].enabled = false;
 
     on_disable_grabber(id);
diff --git a/src/slic3r/GUI/Gizmos/GLGizmoRotate.hpp b/src/slic3r/GUI/Gizmos/GLGizmoRotate.hpp
index 7846edb22..8733c9a11 100644
--- a/src/slic3r/GUI/Gizmos/GLGizmoRotate.hpp
+++ b/src/slic3r/GUI/Gizmos/GLGizmoRotate.hpp
@@ -93,19 +93,19 @@ protected:
     }
     virtual void on_set_hover_id()
     {
-        for (unsigned int i = 0; i < 3; ++i)
+        for (int i = 0; i < 3; ++i)
         {
             m_gizmos[i].set_hover_id((m_hover_id == i) ? 0 : -1);
         }
     }
     virtual void on_enable_grabber(unsigned int id)
     {
-        if ((0 <= id) && (id < 3))
+        if (id < 3)
             m_gizmos[id].enable_grabber(0);
     }
     virtual void on_disable_grabber(unsigned int id)
     {
-        if ((0 <= id) && (id < 3))
+        if (id < 3)
             m_gizmos[id].disable_grabber(0);
     }
     virtual void on_start_dragging();
diff --git a/src/slic3r/GUI/Gizmos/GLGizmoSlaSupports.cpp b/src/slic3r/GUI/Gizmos/GLGizmoSlaSupports.cpp
index 8027906a9..6875a5b88 100644
--- a/src/slic3r/GUI/Gizmos/GLGizmoSlaSupports.cpp
+++ b/src/slic3r/GUI/Gizmos/GLGizmoSlaSupports.cpp
@@ -82,7 +82,9 @@ void GLGizmoSlaSupports::set_sla_support_data(ModelObject* model_object, const S
             editing_mode_reload_cache();
         }
 
-        if (m_editing_mode_cache.empty() && m_model_object->sla_points_status != sla::PointsStatus::UserModified)
+        if (m_editing_mode_cache.empty()
+         && m_model_object->sla_points_status != sla::PointsStatus::UserModified
+         && m_model_object->sla_points_status != sla::PointsStatus::None)
             get_data_from_backend();
 
         if (m_state == On) {
@@ -1122,9 +1124,13 @@ void GLGizmoSlaSupports::on_start_dragging()
 
 void GLGizmoSlaSupports::on_load(cereal::BinaryInputArchive& ar)
 {
+    if (m_editing_mode)
+        editing_mode_discard_changes();
+
     ar(m_clipping_plane_distance,
        m_clipping_plane_normal,
-       m_current_mesh_object_id
+       m_current_mesh_object_id,
+       m_editing_mode_cache
     );
 }
 
@@ -1134,7 +1140,8 @@ void GLGizmoSlaSupports::on_save(cereal::BinaryOutputArchive& ar) const
 {
     ar(m_clipping_plane_distance,
        m_clipping_plane_normal,
-       m_current_mesh_object_id
+       m_current_mesh_object_id,
+       m_editing_mode_cache
     );
 }
 
@@ -1177,16 +1184,16 @@ void GLGizmoSlaSupports::editing_mode_discard_changes()
     // If the points were autogenerated, they may not be on the ModelObject yet.
     // Because the user probably messed with the cache, we will get the data
     // from the backend again.
-
-    if (m_model_object->sla_points_status == sla::PointsStatus::AutoGenerated)
+    /*if (m_model_object->sla_points_status == sla::PointsStatus::AutoGenerated) {
         get_data_from_backend();
-    else {
-        m_editing_mode_cache.clear();
-        for (const sla::SupportPoint& point : m_model_object->sla_support_points)
-            m_editing_mode_cache.emplace_back(point, false);
-    }
-        m_editing_mode = false;
-        m_unsaved_changes = false;
+        }
+    else
+        editing_mode_reload_cache();*/
+
+    m_editing_mode_cache = m_old_cache;
+
+    m_editing_mode = false;
+    m_unsaved_changes = false;
 }
 
 
@@ -1196,7 +1203,13 @@ void GLGizmoSlaSupports::editing_mode_apply_changes()
     // If there are no changes, don't touch the front-end. The data in the cache could have been
     // taken from the backend and copying them to ModelObject would needlessly invalidate them.
     if (m_unsaved_changes) {
+        // In order to make the undo/redo snapshot, we must first temporarily restore
+        // the editing cache to the state before the edits were made.
+        std::vector<CacheEntry> backup = m_editing_mode_cache;
+        m_editing_mode_cache = m_old_cache;
         wxGetApp().plater()->take_snapshot(_(L("Support points edit")));
+        m_editing_mode_cache = std::move(backup);
+
         m_model_object->sla_points_status = sla::PointsStatus::UserModified;
         m_model_object->sla_support_points.clear();
         for (const CacheEntry& cache_entry : m_editing_mode_cache)
@@ -1216,6 +1229,7 @@ void GLGizmoSlaSupports::editing_mode_apply_changes()
 void GLGizmoSlaSupports::editing_mode_reload_cache()
 {
     m_editing_mode_cache.clear();
+
     for (const sla::SupportPoint& point : m_model_object->sla_support_points)
         m_editing_mode_cache.emplace_back(point, false);
 
@@ -1271,6 +1285,8 @@ void GLGizmoSlaSupports::switch_to_editing_mode()
         editing_mode_reload_cache();
     m_unsaved_changes = false;
     m_editing_mode = true;
+    m_old_cache = m_editing_mode_cache;
+    select_point(NoPoints);
 }
 
 
diff --git a/src/slic3r/GUI/Gizmos/GLGizmoSlaSupports.hpp b/src/slic3r/GUI/Gizmos/GLGizmoSlaSupports.hpp
index fbc438f1d..5ef1e6aea 100644
--- a/src/slic3r/GUI/Gizmos/GLGizmoSlaSupports.hpp
+++ b/src/slic3r/GUI/Gizmos/GLGizmoSlaSupports.hpp
@@ -98,6 +98,8 @@ private:
     float m_new_point_head_diameter;        // Size of a new point.
     float m_minimal_point_distance = 20.f;
     mutable std::vector<CacheEntry> m_editing_mode_cache; // a support point and whether it is currently selected
+    std::vector<CacheEntry> m_old_cache; // to restore after discarding changes or undo/redo
+
     float m_clipping_plane_distance = 0.f;
     mutable float m_old_clipping_plane_distance = 0.f;
     mutable Vec3d m_old_clipping_plane_normal;
diff --git a/src/slic3r/GUI/Gizmos/GLGizmosManager.cpp b/src/slic3r/GUI/Gizmos/GLGizmosManager.cpp
index 2aaf55424..d96b806e5 100644
--- a/src/slic3r/GUI/Gizmos/GLGizmosManager.cpp
+++ b/src/slic3r/GUI/Gizmos/GLGizmosManager.cpp
@@ -223,7 +223,7 @@ void GLGizmosManager::update_data()
     enable_grabber(Rotate, 1, !is_wipe_tower);
 
     bool enable_scale_xyz = selection.is_single_full_instance() || selection.is_single_volume() || selection.is_single_modifier();
-    for (int i = 0; i < 6; ++i)
+    for (unsigned int i = 0; i < 6; ++i)
     {
         enable_grabber(Scale, i, enable_scale_xyz);
     }
diff --git a/src/slic3r/GUI/Plater.cpp b/src/slic3r/GUI/Plater.cpp
index f615e4958..7653a5833 100644
--- a/src/slic3r/GUI/Plater.cpp
+++ b/src/slic3r/GUI/Plater.cpp
@@ -3912,8 +3912,6 @@ void Plater::load_project()
     // Ask user for a project file name.
     wxString input_file;
     wxGetApp().load_project(this, input_file);
-    // Take the Undo / Redo snapshot.
-	Plater::TakeSnapshot snapshot(this, _(L("Load Project")) + ": " + wxString::FromUTF8(into_path(input_file).stem().string().c_str()));
     // And finally load the new project.
     load_project(input_file);
 }
@@ -3923,6 +3921,9 @@ void Plater::load_project(const wxString& filename)
     if (filename.empty())
         return;
 
+    // Take the Undo / Redo snapshot.
+    Plater::TakeSnapshot snapshot(this, _(L("Load Project")) + ": " + wxString::FromUTF8(into_path(filename).stem().string().c_str()));
+
     p->reset();
     p->set_project_filename(filename);
 
diff --git a/src/slic3r/GUI/Tab.cpp b/src/slic3r/GUI/Tab.cpp
index b52f9dd46..cb8bb0b6d 100644
--- a/src/slic3r/GUI/Tab.cpp
+++ b/src/slic3r/GUI/Tab.cpp
@@ -1892,8 +1892,35 @@ void TabPrinter::build_fff()
 					extruders_count_changed(extruders_count);
                     init_options_list(); // m_options_list should be updated before UI updating
 					update_dirty();
-                    if (opt_key == "single_extruder_multi_material") // the single_extruder_multimaterial was added to force pages
+                    if (opt_key == "single_extruder_multi_material") { // the single_extruder_multimaterial was added to force pages
                         on_value_change(opt_key, value);                      // rebuild - let's make sure the on_value_change is not skipped
+
+                        if (boost::any_cast<bool>(value) && m_extruders_count > 1) {
+                            SuppressBackgroundProcessingUpdate sbpu;
+                            std::vector<double> nozzle_diameters = static_cast<const ConfigOptionFloats*>(m_config->option("nozzle_diameter"))->values;
+                            const double frst_diam = nozzle_diameters[0];
+
+                            for (auto cur_diam : nozzle_diameters) {
+                                // if value is differs from first nozzle diameter value
+                                if (fabs(cur_diam - frst_diam) > EPSILON) {
+                                    const wxString msg_text = _(L("Single Extruder Multi Material is selected, \n"
+                                                                  "and all extruders must have the same diameter.\n"
+                                                                  "Do you want to change the diameter for all extruders to first extruder nozzle diameter value?"));
+                                    auto dialog = new wxMessageDialog(parent(), msg_text, _(L("Nozzle diameter")), wxICON_WARNING | wxYES_NO);
+                                    
+                                    if (dialog->ShowModal() == wxID_YES) {
+                                        DynamicPrintConfig new_conf = *m_config;
+                                        for (size_t i = 1; i < nozzle_diameters.size(); i++)
+                                            nozzle_diameters[i] = frst_diam;
+
+                                        new_conf.set_key_value("nozzle_diameter", new ConfigOptionFloats(nozzle_diameters));
+                                        load_config(new_conf);
+                                    }
+                                    break;
+                                }
+                            } 
+                        }
+                    }
 				}
 				else {
 					update_dirty();
@@ -2318,7 +2345,7 @@ void TabPrinter::build_unregular_pages()
 
             optgroup->m_on_change = [this, extruder_idx](const t_config_option_key& opt_key, boost::any value)
             {
-                if (m_extruders_count > 1 && opt_key.find_first_of("nozzle_diameter") != std::string::npos)
+                if (m_config->opt_bool("single_extruder_multi_material") && m_extruders_count > 1 && opt_key.find_first_of("nozzle_diameter") != std::string::npos)
                 {
                     SuppressBackgroundProcessingUpdate sbpu;
                     const double new_nd = boost::any_cast<double>(value);
diff --git a/src/slic3r/GUI/wxExtensions.hpp b/src/slic3r/GUI/wxExtensions.hpp
index 9a6460dcb..a704f79d7 100644
--- a/src/slic3r/GUI/wxExtensions.hpp
+++ b/src/slic3r/GUI/wxExtensions.hpp
@@ -323,9 +323,9 @@ public:
 	}
 
 	bool SwapChildrens(int frst_id, int scnd_id) {
-		if (GetChildCount() < 2 || 
-			frst_id < 0 || frst_id >= GetChildCount() || 
-			scnd_id < 0 || scnd_id >= GetChildCount())
+		if (GetChildCount() < 2 ||
+			frst_id < 0 || (size_t)frst_id >= GetChildCount() ||
+			scnd_id < 0 || (size_t)scnd_id >= GetChildCount())
 			return false;
 
 		ObjectDataViewModelNode new_scnd = *GetNthChild(frst_id);
diff --git a/src/slic3r/Utils/UndoRedo.cpp b/src/slic3r/Utils/UndoRedo.cpp
index 72e7431bd..eba839ffb 100644
--- a/src/slic3r/Utils/UndoRedo.cpp
+++ b/src/slic3r/Utils/UndoRedo.cpp
@@ -17,6 +17,7 @@
 #define CEREAL_FUTURE_EXPERIMENTAL
 #include <cereal/archives/adapters.hpp>
 
+#include <libslic3r/Config.hpp>
 #include <libslic3r/ObjectID.hpp>
 #include <libslic3r/Utils.hpp>