Optimize string (mis)handling (#8128)

* Optimize statbar drawing

The texture name of the statbar is a string passed by value.
That slows down the client and creates litter in the heap
as the content of the string is allocated there. Convert the
offending parameter to a const reference to avoid the
performance hit.

* Optimize texture cache

There is an unnecessary temporary created when the texture
path is being generated. This slows down the cache each time
a new texture is encountered and it needs to be loaded into
the cache. Additionally, the heap litter created by this
unnecessary temporary is particularly troublesome here as
the following code then piles another string (the resulting
full path of the texture) on top of it, followed by the
texture itself, which both are quite long term objects as
they are subsequently inserted into the cache where they can
remain for quite a while (especially if the texture turns
out to be a common one like dirt, grass or stone).

Use std::string.append to get rid of the temporary which
solves both issues (speed and heap fragmentation).

* Optimize animations in client

Each time an animated node is updated, an unnecessary copy of
the texture name is created, littering the heap with lots of
fragments. This can be specifically troublesome when looking
at oceans or large lava lakes as both of these nodes are
usually animated (the lava animation is pretty visible).
Convert the parameter of GenericCAO::updateTextures to a
const reference to get rid of the unnecessary copy.

There is a comment stating "std::string copy is mandatory as
mod can be a class member and there is a swap on those class
members ... do NOT pass by reference", reinforcing the
belief that the unnecessary copy is in fact necessary.
However one of the first things the code of the method does
is to assign the parameter to its class member, creating
another copy. By rearranging the code a little bit this
"another copy" can then be used by the subsequent code,
getting rid of the need to pass the parameter by value and
thus saving that copying effort.

* Optimize chat console history handling

The GUIChatConsole::replaceAndAddToHistory was getting the
line to work on by value which turns out to be unnecessary.
Get rid of that unnecessary copy by converting the parameter
to a const reference.

* Optimize gui texture setting

The code used to set the texture for GUI components was
getting the name of the texture by value, creating
unnecessary performance bottleneck for mods/games with
heavily textured GUIs. Get rid of the bottleneck by passing
the texture name as a const reference.

* Optimize sound playing code in GUIEngine

The GUIEngine's code receives the specification of the sound
to be played by value, which turns out to be most likely a
mistake as the underlying sound manager interface receives
the same thing by reference. Convert the offending parameter
to a const reference to get rid of the rather bulky copying
effort and the associated performance hit.

* Silence CLANG TIDY warnings for unit tests

Change "std::string" to "const std::string &" to avoid an
unnecessary local value copy, silencing the CLANG TIDY
process.

* Optimize formspec handling

The "formspec prepend" parameter was passed to the formspec
handling code by value, creating unnecessary copy of
std::string and slowing down the game if mods add things like
textured backgrounds for the player inventory and/or other
forms. Get rid of that performance bottleneck by converting
the parameter to a const reference.

* Optimize hotbar image handling

The code that sets the background images for the hotbar is
getting the name of the image by value, creating an
unnecessary std::string copying effort. Fix that by
converting the relevant parameters to const references.

* Optimize inventory deserialization

The inventory manager deserialization code gets the
serialized version of the inventory by value, slowing the
server and the client down when there are inventory updates.
This can get particularly troublesome with pipeworks which
adds nodes that can mess around with inventories
automatically or with mods that have mobs with inventories
that actively use them.

* Optimize texture scaling cache

There is an io::path parameter passed by value in the
procedure used to add images converted from textures,
leading to slowdown when the image is not yet created and
the conversion is thus needed. The performance hit is
quite significant as io::path is similar to std::string
so convert the parameter to a const reference to get rid of
it.

* Optimize translation file loader

Use "std::string::append" when calculating the final index
for the translation table to avoid unnecessary temporary
strings. This speeds the translation file loader up
significantly as std::string uses heap allocation which
tends to be rather slow. Additionally, the heap is no
longer being littered by these unnecessary string
temporaries, increasing performance of code that gets
executed after the translation file loader finishes.

* Optimize server map saving

When the directory structure for the world data is created
during server map saving, an unnecessary value passing of
the directory name slows things down. Remove that overhead
by converting the offending parameter to a const reference.

21 files changed, 41 insertions, 28 deletions

diff --git a/src/client/content_cao.cpp b/src/client/content_cao.cpp
index b169ba75f..cf22aa0ed 100644
--- a/src/client/content_cao.cpp
+++ b/src/client/content_cao.cpp
@@ -1062,7 +1062,7 @@ void GenericCAO::updateTexturePos()
 	}
 }
 
-void GenericCAO::updateTextures(std::string mod)
+void GenericCAO::updateTextures(const std::string &modref)
 {
 	ITextureSource *tsrc = m_client->tsrc();
 
@@ -1071,9 +1071,21 @@ void GenericCAO::updateTextures(std::string mod)
 	bool use_anisotropic_filter = g_settings->getBool("anisotropic_filter");
 
 	m_previous_texture_modifier = m_current_texture_modifier;
-	m_current_texture_modifier = mod;
+	m_current_texture_modifier = modref;
 	m_glow = m_prop.glow;
 
+	// Create a reference to the copy of "modref" just created. The
+	// following code will then use this reference instead of the
+	// original parameter which was passed by reference. This is
+	// necessary as "modref" can be a class member and there is a swap on
+	// those class members which can get triggered by the rest of the
+	// code of this method. This is faster than passing the "mod" by
+	// value because it reuses the copy made by the assignment to
+	// m_current_texture_modifier for the "mod" instead of having two
+	// copies, one for "mod" and another one (created from "mod") for
+	// the m_current_texture_modifier class member.
+	const std::string &mod = m_current_texture_modifier;
+
 	video::E_MATERIAL_TYPE material_type = (m_prop.use_texture_alpha) ?
 		video::EMT_TRANSPARENT_ALPHA_CHANNEL : video::EMT_TRANSPARENT_ALPHA_CHANNEL_REF;
 
diff --git a/src/client/content_cao.h b/src/client/content_cao.h
index 3ce628d30..320607061 100644
--- a/src/client/content_cao.h
+++ b/src/client/content_cao.h
@@ -225,9 +225,7 @@ public:
 
 	void updateTexturePos();
 
-	// std::string copy is mandatory as mod can be a class member and there is a swap
-	// on those class members... do NOT pass by reference
-	void updateTextures(std::string mod);
+	void updateTextures(const std::string &modref);
 
 	void updateAnimation();
 
diff --git a/src/client/guiscalingfilter.cpp b/src/client/guiscalingfilter.cpp
index 3b4377da5..312f93939 100644
--- a/src/client/guiscalingfilter.cpp
+++ b/src/client/guiscalingfilter.cpp
@@ -39,7 +39,7 @@ std::map<io::path, video::ITexture *> g_txrCache;
 /* Manually insert an image into the cache, useful to avoid texture-to-image
  * conversion whenever we can intercept it.
  */
-void guiScalingCache(io::path key, video::IVideoDriver *driver, video::IImage *value)
+void guiScalingCache(const io::path &key, video::IVideoDriver *driver, video::IImage *value)
 {
 	if (!g_settings->getBool("gui_scaling_filter"))
 		return;
diff --git a/src/client/guiscalingfilter.h b/src/client/guiscalingfilter.h
index 4661bf8da..a5cd78511 100644
--- a/src/client/guiscalingfilter.h
+++ b/src/client/guiscalingfilter.h
@@ -23,7 +23,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 /* Manually insert an image into the cache, useful to avoid texture-to-image
  * conversion whenever we can intercept it.
  */
-void guiScalingCache(io::path key, video::IVideoDriver *driver, video::IImage *value);
+void guiScalingCache(const io::path &key, video::IVideoDriver *driver, video::IImage *value);
 
 // Manually clear the cache, e.g. when switching to different worlds.
 void guiScalingCacheClear();
diff --git a/src/client/hud.cpp b/src/client/hud.cpp
index 1a2287a13..cb58fb500 100644
--- a/src/client/hud.cpp
+++ b/src/client/hud.cpp
@@ -372,7 +372,7 @@ void Hud::drawLuaElements(const v3s16 &camera_offset)
 }
 
 
-void Hud::drawStatbar(v2s32 pos, u16 corner, u16 drawdir, std::string texture,
+void Hud::drawStatbar(v2s32 pos, u16 corner, u16 drawdir, const std::string &texture,
 		s32 count, v2s32 offset, v2s32 size)
 {
 	const video::SColor color(255, 255, 255, 255);
diff --git a/src/client/hud.h b/src/client/hud.h
index e9bcdf4e2..693d2adee 100644
--- a/src/client/hud.h
+++ b/src/client/hud.h
@@ -81,7 +81,7 @@ public:
 	void drawLuaElements(const v3s16 &camera_offset);
 
 private:
-	void drawStatbar(v2s32 pos, u16 corner, u16 drawdir, std::string texture,
+	void drawStatbar(v2s32 pos, u16 corner, u16 drawdir, const std::string &texture,
 			s32 count, v2s32 offset, v2s32 size = v2s32());
 
 	void drawItems(v2s32 upperleftpos, v2s32 screen_offset, s32 itemcount,
diff --git a/src/client/tile.cpp b/src/client/tile.cpp
index 4911013ae..72f7358b1 100644
--- a/src/client/tile.cpp
+++ b/src/client/tile.cpp
@@ -131,7 +131,8 @@ std::string getTexturePath(const std::string &filename)
 		Check from texture_path
 	*/
 	for (const auto &path : getTextureDirs()) {
-		std::string testpath = path + DIR_DELIM + filename;
+		std::string testpath = path + DIR_DELIM;
+		testpath.append(filename);
 		// Check all filename extensions. Returns "" if not found.
 		fullpath = getImagePath(testpath);
 		if (!fullpath.empty())
diff --git a/src/gui/guiChatConsole.cpp b/src/gui/guiChatConsole.cpp
index 1ccb4e6d1..42348beb3 100644
--- a/src/gui/guiChatConsole.cpp
+++ b/src/gui/guiChatConsole.cpp
@@ -139,7 +139,7 @@ f32 GUIChatConsole::getDesiredHeight() const
 	return m_desired_height_fraction;
 }
 
-void GUIChatConsole::replaceAndAddToHistory(std::wstring line)
+void GUIChatConsole::replaceAndAddToHistory(const std::wstring &line)
 {
 	ChatPrompt& prompt = m_chat_backend->getPrompt();
 	prompt.addToHistory(prompt.getLine());
diff --git a/src/gui/guiChatConsole.h b/src/gui/guiChatConsole.h
index ef8a87673..7be40e27c 100644
--- a/src/gui/guiChatConsole.h
+++ b/src/gui/guiChatConsole.h
@@ -60,7 +60,7 @@ public:
 	f32 getDesiredHeight() const;
 
 	// Replace actual line when adding the actual to the history (if there is any)
-	void replaceAndAddToHistory(std::wstring line);
+	void replaceAndAddToHistory(const std::wstring &line);
 
 	// Change how the cursor looks
 	void setCursor(
diff --git a/src/gui/guiEngine.cpp b/src/gui/guiEngine.cpp
index 6030a5bfb..f0a8f40eb 100644
--- a/src/gui/guiEngine.cpp
+++ b/src/gui/guiEngine.cpp
@@ -518,7 +518,7 @@ void GUIEngine::drawFooter(video::IVideoDriver *driver)
 }
 
 /******************************************************************************/
-bool GUIEngine::setTexture(texture_layer layer, std::string texturepath,
+bool GUIEngine::setTexture(texture_layer layer, const std::string &texturepath,
 		bool tile_image, unsigned int minsize)
 {
 	video::IVideoDriver *driver = RenderingEngine::get_video_driver();
@@ -593,7 +593,7 @@ void GUIEngine::updateTopLeftTextSize()
 }
 
 /******************************************************************************/
-s32 GUIEngine::playSound(SimpleSoundSpec spec, bool looped)
+s32 GUIEngine::playSound(const SimpleSoundSpec &spec, bool looped)
 {
 	s32 handle = m_sound_manager->playSound(spec, looped);
 	return handle;
diff --git a/src/gui/guiEngine.h b/src/gui/guiEngine.h
index 409ba94c4..0ff5030c0 100644
--- a/src/gui/guiEngine.h
+++ b/src/gui/guiEngine.h
@@ -247,7 +247,7 @@ private:
 	 * @param layer draw layer to specify texture
 	 * @param texturepath full path of texture to load
 	 */
-	bool setTexture(texture_layer layer, std::string texturepath,
+	bool setTexture(texture_layer layer, const std::string &texturepath,
 			bool tile_image, unsigned int minsize);
 
 	/**
@@ -296,7 +296,7 @@ private:
 	clouddata   m_cloud;
 
 	/** start playing a sound and return handle */
-	s32 playSound(SimpleSoundSpec spec, bool looped);
+	s32 playSound(const SimpleSoundSpec &spec, bool looped);
 	/** stop playing a sound started with playSound() */
 	void stopSound(s32 handle);
 
diff --git a/src/gui/guiFormSpecMenu.cpp b/src/gui/guiFormSpecMenu.cpp
index 92e654765..e2aed420c 100644
--- a/src/gui/guiFormSpecMenu.cpp
+++ b/src/gui/guiFormSpecMenu.cpp
@@ -86,7 +86,7 @@ inline u32 clamp_u8(s32 value)
 GUIFormSpecMenu::GUIFormSpecMenu(JoystickController *joystick,
 		gui::IGUIElement *parent, s32 id, IMenuManager *menumgr,
 		Client *client, ISimpleTextureSource *tsrc, IFormSource *fsrc, TextDest *tdst,
-		std::string formspecPrepend,
+		const std::string &formspecPrepend,
 		bool remap_dbl_click):
 	GUIModalMenu(RenderingEngine::get_gui_env(), parent, id, menumgr),
 	m_invmgr(client),
diff --git a/src/gui/guiFormSpecMenu.h b/src/gui/guiFormSpecMenu.h
index d75a108d4..33f88d8c0 100644
--- a/src/gui/guiFormSpecMenu.h
+++ b/src/gui/guiFormSpecMenu.h
@@ -287,7 +287,7 @@ public:
 			ISimpleTextureSource *tsrc,
 			IFormSource* fs_src,
 			TextDest* txt_dst,
-			std::string formspecPrepend,
+			const std::string &formspecPrepend,
 			bool remap_dbl_click = true);
 
 	~GUIFormSpecMenu();
diff --git a/src/inventorymanager.cpp b/src/inventorymanager.cpp
index 51a472a56..24d1fa6ff 100644
--- a/src/inventorymanager.cpp
+++ b/src/inventorymanager.cpp
@@ -93,7 +93,7 @@ void InventoryLocation::deSerialize(std::istream &is)
 	}
 }
 
-void InventoryLocation::deSerialize(std::string s)
+void InventoryLocation::deSerialize(const std::string &s)
 {
 	std::istringstream is(s, std::ios::binary);
 	deSerialize(is);
diff --git a/src/inventorymanager.h b/src/inventorymanager.h
index 30a82d4bf..06517f40f 100644
--- a/src/inventorymanager.h
+++ b/src/inventorymanager.h
@@ -97,7 +97,7 @@ struct InventoryLocation
 	std::string dump() const;
 	void serialize(std::ostream &os) const;
 	void deSerialize(std::istream &is);
-	void deSerialize(std::string s);
+	void deSerialize(const std::string &s);
 };
 
 struct InventoryAction;
diff --git a/src/map.cpp b/src/map.cpp
index 0114867e0..3d1e74790 100644
--- a/src/map.cpp
+++ b/src/map.cpp
@@ -1717,7 +1717,7 @@ bool ServerMap::loadFromFolders() {
 	return false;
 }
 
-void ServerMap::createDirs(std::string path)
+void ServerMap::createDirs(const std::string &path)
 {
 	if (!fs::CreateAllDirs(path)) {
 		m_dout<<"ServerMap: Failed to create directory "
diff --git a/src/map.h b/src/map.h
index 7ef34b279..251ac297f 100644
--- a/src/map.h
+++ b/src/map.h
@@ -389,7 +389,7 @@ public:
 		Misc. helper functions for fiddling with directory and file
 		names when saving
 	*/
-	void createDirs(std::string path);
+	void createDirs(const std::string &path);
 	// returns something like "map/sectors/xxxxxxxx"
 	std::string getSectorDir(v2s16 pos, int layout = 2);
 	// dirname: final directory name
diff --git a/src/server.cpp b/src/server.cpp
index 496170da3..7167a6686 100644
--- a/src/server.cpp
+++ b/src/server.cpp
@@ -3207,7 +3207,7 @@ bool Server::hudSetHotbarItemcount(RemotePlayer *player, s32 hotbar_itemcount)
 	return true;
 }
 
-void Server::hudSetHotbarImage(RemotePlayer *player, std::string name)
+void Server::hudSetHotbarImage(RemotePlayer *player, const std::string &name)
 {
 	if (!player)
 		return;
@@ -3216,7 +3216,7 @@ void Server::hudSetHotbarImage(RemotePlayer *player, std::string name)
 	SendHUDSetParam(player->getPeerId(), HUD_PARAM_HOTBAR_IMAGE, name);
 }
 
-void Server::hudSetHotbarSelectedImage(RemotePlayer *player, std::string name)
+void Server::hudSetHotbarSelectedImage(RemotePlayer *player, const std::string &name)
 {
 	if (!player)
 		return;
diff --git a/src/server.h b/src/server.h
index 5e58ac9e6..4232653eb 100644
--- a/src/server.h
+++ b/src/server.h
@@ -296,8 +296,8 @@ public:
 	bool hudChange(RemotePlayer *player, u32 id, HudElementStat stat, void *value);
 	bool hudSetFlags(RemotePlayer *player, u32 flags, u32 mask);
 	bool hudSetHotbarItemcount(RemotePlayer *player, s32 hotbar_itemcount);
-	void hudSetHotbarImage(RemotePlayer *player, std::string name);
-	void hudSetHotbarSelectedImage(RemotePlayer *player, std::string name);
+	void hudSetHotbarImage(RemotePlayer *player, const std::string &name);
+	void hudSetHotbarSelectedImage(RemotePlayer *player, const std::string &name);
 
 	Address getPeerAddress(session_t peer_id);
 
diff --git a/src/translation.cpp b/src/translation.cpp
index 7ddd95591..d17467ce7 100644
--- a/src/translation.cpp
+++ b/src/translation.cpp
@@ -149,6 +149,8 @@ void Translations::loadTranslation(const std::string &data)
 			            << wide_to_utf8(oword1) << "\"" << std::endl;
 		}
 
-		m_translations[textdomain + L"|" + oword1] = oword2;
+		std::wstring translation_index = textdomain + L"|";
+		translation_index.append(oword1);
+		m_translations[translation_index] = oword2;
 	}
 }
diff --git a/src/unittest/test_areastore.cpp b/src/unittest/test_areastore.cpp
index 62d446f5c..a6d4706e4 100644
--- a/src/unittest/test_areastore.cpp
+++ b/src/unittest/test_areastore.cpp
@@ -152,7 +152,7 @@ void TestAreaStore::testSerialization()
 			1 + 2 +
 			6 + 6 + 2 + 6 +
 			6 + 6 + 2 + 6);
-	UASSERTEQ(std::string, str, str_wanted);
+	UASSERTEQ(const std::string &, str, str_wanted);
 
 	std::istringstream is(str);
 	store.deserialize(is);