Enable IPO/LTO by default except for debug builds (#14198)

Test case:

```
$ cmake . -DRUN_IN_PLACE=TRUE -DCMAKE_BUILD_TYPE=Release -DBUILD_SERVER=TRUE -DENABLE_TOUCH=FALSE

         minetest minetestserver
W/o LTO:      13M           7.3M
W/  LTO:      11M           5.9M
difference:   15%            19%
```

Also fixes various compiler warnings resulting from compilation using LTO.

---------

Signed-off-by: David Heidelberg <david@ixit.cz>

CMakeLists.txt

@@ -1,11 +1,4 @@
-cmake_minimum_required(VERSION 3.5)
-
-# Set policies up to 3.9 since we want to enable the IPO option
-if(${CMAKE_VERSION} VERSION_LESS 3.9)
-	cmake_policy(VERSION ${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION})
-else()
-	cmake_policy(VERSION 3.9)
-endif()
+cmake_minimum_required(VERSION 3.12)
 
 # This can be read from ${PROJECT_NAME} after project() is called
 project(minetest)
@@ -44,6 +37,13 @@ set(BUILD_UNITTESTS TRUE CACHE BOOL "Build unittests")
 set(BUILD_BENCHMARKS FALSE CACHE BOOL "Build benchmarks")
 set(BUILD_DOCUMENTATION TRUE CACHE BOOL "Build documentation")
 
+set(DEFAULT_ENABLE_LTO TRUE)
+# by default don't enable on Debug builds to get faster builds
+if(CMAKE_BUILD_TYPE STREQUAL "Debug")
+  set(DEFAULT_ENABLE_LTO FALSE)
+endif()
+set(ENABLE_LTO ${DEFAULT_ENABLE_LTO} CACHE BOOL "Use Link Time Optimization")
+
 set(DEFAULT_RUN_IN_PLACE FALSE)
 if(WIN32)
 	set(DEFAULT_RUN_IN_PLACE TRUE)
@@ -66,6 +66,20 @@ if(NOT CMAKE_BUILD_TYPE)
 	set(CMAKE_BUILD_TYPE Release CACHE STRING "Build type: Debug or Release" FORCE)
 endif()
 
+# FIXME: Windows build fails in multiple places to link, needs to be investigated.
+if (ENABLE_LTO AND NOT WIN32)
+	include(CheckIPOSupported)
+	check_ipo_supported(RESULT lto_supported OUTPUT lto_output)
+	if(lto_supported)
+		set(CMAKE_INTERPROCEDURAL_OPTIMIZATION TRUE)
+		message(STATUS "LTO/IPO is enabled")
+	else()
+		message(STATUS "LTO/IPO requested but it is not supported by the compiler: ${lto_output}")
+	endif()
+else()
+	message(STATUS "LTO/IPO is not enabled")
+endif()
+
 set(ENABLE_UPDATE_CHECKER (NOT ${DEVELOPMENT_BUILD}) CACHE BOOL
 	"Whether to enable update checks by default")
 

doc/compiling/README.md

@@ -28,6 +28,7 @@ General options and their default values:
     ENABLE_REDIS=ON            - Build with libhiredis; Enables use of Redis map backend
     ENABLE_SPATIAL=ON          - Build with LibSpatial; Speeds up AreaStores
     ENABLE_SOUND=ON            - Build with OpenAL, libogg & libvorbis; in-game sounds
+    ENABLE_LTO=ON              - Build with IPO/LTO optimizations (smaller and more efficient than regular build)
     ENABLE_LUAJIT=ON           - Build with LuaJIT (much faster than non-JIT Lua)
     ENABLE_PROMETHEUS=OFF      - Build with Prometheus metrics exporter (listens on tcp/30000 by default)
     ENABLE_SYSTEM_GMP=ON       - Use GMP from system (much faster than bundled mini-gmp)

src/client/particles.cpp

@@ -213,10 +213,10 @@ void Particle::step(float dtime)
 
 	if (m_p.animation.type != TAT_NONE) {
 		m_animation_time += dtime;
-		int frame_length_i, frame_count;
+		int frame_length_i = 0;
 		m_p.animation.determineParams(
 				m_material.getTexture(0)->getSize(),
-				&frame_count, &frame_length_i, NULL);
+				NULL, &frame_length_i, NULL);
 		float frame_length = frame_length_i / 1000.0;
 		while (m_animation_time > frame_length) {
 			m_animation_frame++;

src/gui/guiTable.cpp

@@ -210,7 +210,7 @@ void GUITable::setTable(const TableOptions &options,
 	s32 colcount = columns.size();
 	assert(colcount >= 1);
 	// rowcount = ceil(cellcount / colcount) but use integer arithmetic
-	s32 rowcount = (content.size() + colcount - 1) / colcount;
+	s32 rowcount = std::min(((u32)content.size() + colcount - 1) / colcount, (u32)S32_MAX);
 	assert(rowcount >= 0);
 	// Append empty strings to content if there is an incomplete row
 	s32 cellcount = rowcount * colcount;

src/nodedef.cpp

@@ -734,7 +734,7 @@ static void fillTileAttribs(ITextureSource *tsrc, TileLayer *layer,
 	int frame_count = 1;
 	if (layer->material_flags & MATERIAL_FLAG_ANIMATION) {
 		assert(layer->texture);
-		int frame_length_ms;
+		int frame_length_ms = 0;
 		tiledef.animation.determineParams(layer->texture->getOriginalSize(),
 				&frame_count, &frame_length_ms, NULL);
 		layer->animation_frame_count = frame_count;

src/script/lua_api/l_server.cpp

@@ -167,26 +167,6 @@ int ModApiServer::l_get_player_information(lua_State *L)
 		return 1;
 	}
 
-	/*
-		Be careful not to introduce a depdendency on the connection to
-		the peer here. This function is >>REQUIRED<< to still be able to return
-		values even when the peer unexpectedly disappears.
-		Hence all the ConInfo values here are optional.
-	*/
-
-	auto getConInfo = [&] (con::rtt_stat_type type, float *value) -> bool {
-		return server->getClientConInfo(player->getPeerId(), type, value);
-	};
-
-	float min_rtt, max_rtt, avg_rtt, min_jitter, max_jitter, avg_jitter;
-	bool have_con_info =
-		getConInfo(con::MIN_RTT, &min_rtt) &&
-		getConInfo(con::MAX_RTT, &max_rtt) &&
-		getConInfo(con::AVG_RTT, &avg_rtt) &&
-		getConInfo(con::MIN_JITTER, &min_jitter) &&
-		getConInfo(con::MAX_JITTER, &max_jitter) &&
-		getConInfo(con::AVG_JITTER, &avg_jitter);
-
 	ClientInfo info;
 	if (!server->getClientInfo(player->getPeerId(), info)) {
 		warningstream << FUNCTION_NAME << ": no client info?!" << std::endl;
@@ -211,6 +191,26 @@ int ModApiServer::l_get_player_information(lua_State *L)
 	}
 	lua_settable(L, table);
 
+	/*
+		Be careful not to introduce a depdendency on the connection to
+		the peer here. This function is >>REQUIRED<< to still be able to return
+		values even when the peer unexpectedly disappears.
+		Hence all the ConInfo values here are optional.
+	*/
+
+	auto getConInfo = [&] (con::rtt_stat_type type, float *value) -> bool {
+		return server->getClientConInfo(player->getPeerId(), type, value);
+	};
+
+	float min_rtt, max_rtt, avg_rtt, min_jitter, max_jitter, avg_jitter;
+	bool have_con_info =
+		getConInfo(con::MIN_RTT, &min_rtt) &&
+		getConInfo(con::MAX_RTT, &max_rtt) &&
+		getConInfo(con::AVG_RTT, &avg_rtt) &&
+		getConInfo(con::MIN_JITTER, &min_jitter) &&
+		getConInfo(con::MAX_JITTER, &max_jitter) &&
+		getConInfo(con::AVG_JITTER, &avg_jitter);
+
 	if (have_con_info) { // may be missing
 		lua_pushstring(L, "min_rtt");
 		lua_pushnumber(L, min_rtt);

util/ci/build.sh

@@ -1,7 +1,8 @@
-#! /bin/bash -e
+#!/bin/bash -e
 
 cmake -B build \
 	-DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE:-Debug} \
+	-DENABLE_LTO=FALSE \
 	-DRUN_IN_PLACE=TRUE \
 	-DENABLE_GETTEXT=${CMAKE_ENABLE_GETTEXT:-TRUE} \
 	-DBUILD_SERVER=${CMAKE_BUILD_SERVER:-TRUE} \