cmake: rewrite the build options and the flag setting

- Add USE_LTO to enable LTO,
  enabled by default.
- Add USE_EXTRA_OPTIMIZATION to also enable -O3 when it is not used by default
  enabled by default.
- Add USE_FAST_MATH, to produce reproducible CRN files this should be disabled,
  enabled by default.
- Increase warning verbosity level.
- Generate maximum amount of debug information, including macro definitions.
- Always disable strict aliasing, the code requires it to always be disabled.

Fixes #29

CMakeLists.txt

@@ -8,8 +8,11 @@ set(CRUNCH_EXE_NAME crunch)
 
 project(${CRUNCH_PROJECT_NAME})
 
-if(NOT CMAKE_BUILD_TYPE)
-  set(CMAKE_BUILD_TYPE Release)
+set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${PROJECT_BINARY_DIR})
+
+if (NOT CMAKE_BUILD_TYPE)
+	set(CMAKE_BUILD_TYPE "Release" CACHE
+		STRING "Choose the type of build, options are: Debug Release RelWithDebInfo MinSizeRel" FORCE)
 endif()
 
 find_package(Git)
@@ -27,27 +30,108 @@ if (Git_FOUND)
   endif()
 endif()
 
+macro(set_cxx_flag FLAG)
+	if (${ARGC} GREATER 1)
+		set(CMAKE_CXX_FLAGS_${ARGV1} "${CMAKE_CXX_FLAGS_${ARGV1}} ${FLAG}")
+	else()
+		set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${FLAG}")
+	endif()
+endmacro()
+
+macro(set_linker_flag FLAG)
+	if (${ARGC} GREATER 1)
+		set(CMAKE_EXE_LINKER_FLAGS_${ARGV1} "${CMAKE_EXE_LINKER_FLAGS_${ARGV1}} ${FLAG}")
+		set(CMAKE_SHARED_LINKER_FLAGS_${ARGV1} "${CMAKE_SHARED_LINKER_FLAGS_${ARGV1}} ${FLAG}")
+		set(CMAKE_MODULE_LINKER_FLAGS_${ARGV1} "${CMAKE_MODULE_LINKER_FLAGS_${ARGV1}} ${FLAG}")
+	else()
+		set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} ${FLAG}")
+		set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} ${FLAG}")
+		set(CMAKE_MODULE_LINKER_FLAGS "${CMAKE_MODULE_LINKER_FLAGS} ${FLAG}")
+	endif()
+endmacro()
+
+# This option decides if crunch is dynamically linked against libcrn.so
+# statically linked against libcrn.o, enabling it always build libcrn.so.
+# This option is a builtin CMake one, the name means “build executables
+# against shader libraries”, not “build the shared libraries”.
 option(BUILD_SHARED_LIBS "Link executables against shared library" OFF)
+# Always build libcrn.so even if crunch is linked to libcrn statically.
 option(BUILD_SHARED_LIBCRN "Build shared libcrn" OFF)
+# Always build libcrn.a even if crunch is linked to libcrn dynamically.
 option(BUILD_STATIC_LIBCRN "Build static libcrn" OFF)
+# Build the crunch tool, implies the build of libcrn.o or libcrn.so.
 option(BUILD_CRUNCH "Build crunch" ON)
+# Build the provided examples, they only build on Windows for now.
 option(BUILD_EXAMPLES "Build examples" OFF)
-if (NOT MSVC)
-  option(OPTIMIZE_RELEASE "Optimize release build" ON)
-endif()
+# Enable extra optimization flags, like using -O3 even in RelWithDebInfo build.
+option(USE_EXTRA_OPTIMIZATION "Enable extra optimization" ON)
+# Enable link time optimization, slows down the build but produce faster and smaller binaries.
+option(USE_LTO "Enable link-time optimization" ON)
+# Enabling fast math makes generated images less likely to be reproducible.
+# See https://github.com/DaemonEngine/crunch/issues/29
+option(USE_FAST_MATH "Enable fast math (generated images are less likely to be reproducible)" ON)
 
-set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${PROJECT_BINARY_DIR})
+if (MSVC)
+	# Enable MSVC parallel compilation.
+	set_cxx_flag("/MP")
 
-if (NOT MSVC)
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wno-unused-value -Wno-unused")
-endif()
+	# MSVC doesn't implement strict aliasing so there is nothing else to do.
+
+	# Increase warning verbosity level.
+	set_cxx_flag("/W4")
+
+	# CMake already sets the /O2 flag on Release and RelWithDebInfo build and /O[1-2] already sets the /Oy flag.
 
-if(OPTIMIZE_RELEASE)
-  # CMake already sets -O3 flag on release build
-  set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} -fomit-frame-pointer -ffast-math -fno-math-errno -fno-strict-aliasing")
+	if (USE_FAST_MATH)
+		set_cxx_flag("/fp:fast")
+	endif()
+
+	if (USE_LTO)
+		set_cxx_flag("/GL" RELEASE)
+		set_cxx_flag("/GL" RELWITHDEBINFO)
+		set_cxx_flag("/GL" MINSIZEREL)
+		set_linker_flag("/LTCG" RELEASE)
+		set_linker_flag("/LTCG" RELWITHDEBINFO)
+		set_linker_flag("/LTCG" MINSIZEREL)
+	endif()
+else()
+	# As written in crnlib.h and stb_image.h, strict aliasing should always be disabled.
+	set_cxx_flag("-fno-strict-aliasing")
+
+	# Generate maxmimum amount of debug information, including macro definitions.
+	set_cxx_flag("-g3" DEBUG)
+	set_cxx_flag("-g3" RELWITHDEBINFO)
+
+	# Increase warning verbosity level.
+	set_cxx_flag("-Wall")
+	set_cxx_flag("-Wno-unused-value")
+	set_cxx_flag("-Wno-unused")
+
+	if (USE_EXTRA_OPTIMIZATION)
+		# CMake already sets the -O3 flag on Release build and -O[1-3s] already sets the -fomit-frame-pointer flag.
+		set_cxx_flag("-Og" DEBUG)
+		set_cxx_flag("-O3" RELWITHDEBINFO)
+	endif()
+
+	if (USE_FAST_MATH)
+		set_cxx_flag("-ffast-math -fno-math-errno")
+	endif()
+
+	# It should be done at the very end because it copies all compiler flags
+	# to the linker flags.
+	if (USE_LTO)
+		set_cxx_flag("-flto" RELEASE)
+		set_cxx_flag("-flto" RELWITHDEBINFO)
+		set_cxx_flag("-flto" MINSIZEREL)
+		set_linker_flag("${CMAKE_CXX_FLAGS}" RELEASE)
+		set_linker_flag("${CMAKE_CXX_FLAGS}" RELWITHDEBINFO)
+		set_linker_flag("${CMAKE_CXX_FLAGS}" MINSIZEREL)
+	endif()
 endif()
 
-add_subdirectory(crnlib)
+if (BUILD_SHARED_LIBCRN OR BUILD_STATIC_LIBCRN OR BUILD_CRUNCH)
+  add_subdirectory(crnlib crnlib)
+endif()
 
 if (BUILD_CRUNCH)
   add_subdirectory(crunch _crunch)