Merge pull request godotengine#1601 from Ivorforce/lto

Add lto scons option

Author: dsnopek

tools/android.py

@@ -120,4 +120,9 @@ def generate(env):
 
  env.Append(CPPDEFINES=["ANDROID_ENABLED", "UNIX_ENABLED"])
 
+ # Refer to https://github.com/godotengine/godot/blob/master/platform/android/detect.py
+ # LTO benefits for Android (size, performance) haven't been clearly established yet.
+ if env["lto"] == "auto":
+ env["lto"] = "none"
+
  common_compiler_flags.generate(env)

tools/common_compiler_flags.py

@@ -22,6 +22,10 @@ def exists(env):
 
 
 def generate(env):
+ assert env["lto"] in ["thin", "full", "none"], "Unrecognized lto: {}".format(env["lto"])
+ if env["lto"] != "none":
+ print("Using LTO: " + env["lto"])
+
  # Require C++17
  if env.get("is_msvc", False):
  env.Append(CXXFLAGS=["/std:c++17"])
@@ -64,6 +68,22 @@ def generate(env):
  env.Append(LINKFLAGS=["/OPT:REF"])
  elif env["optimize"] == "debug" or env["optimize"] == "none":
  env.Append(CCFLAGS=["/Od"])
+
+ if env["lto"] == "thin":
+ if not env["use_llvm"]:
+ print("ThinLTO is only compatible with LLVM, use `use_llvm=yes` or `lto=full`.")
+ env.Exit(255)
+
+ env.Append(CCFLAGS=["-flto=thin"])
+ env.Append(LINKFLAGS=["-flto=thin"])
+ elif env["lto"] == "full":
+ if env["use_llvm"]:
+ env.Append(CCFLAGS=["-flto"])
+ env.Append(LINKFLAGS=["-flto"])
+ else:
+ env.AppendUnique(CCFLAGS=["/GL"])
+ env.AppendUnique(ARFLAGS=["/LTCG"])
+ env.AppendUnique(LINKFLAGS=["/LTCG"])
  else:
  if env["debug_symbols"]:
  # Adding dwarf-4 explicitly makes stacktraces work with clang builds,
@@ -91,3 +111,13 @@ def generate(env):
  env.Append(CCFLAGS=["-Og"])
  elif env["optimize"] == "none":
  env.Append(CCFLAGS=["-O0"])
+
+ if env["lto"] == "thin":
+ if (env["platform"] == "windows" or env["platform"] == "linux") and not env["use_llvm"]:
+ print("ThinLTO is only compatible with LLVM, use `use_llvm=yes` or `lto=full`.")
+ env.Exit(255)
+ env.Append(CCFLAGS=["-flto=thin"])
+ env.Append(LINKFLAGS=["-flto=thin"])
+ elif env["lto"] == "full":
+ env.Append(CCFLAGS=["-flto"])
+ env.Append(LINKFLAGS=["-flto"])

tools/godotcpp.py

@@ -326,6 +326,14 @@ def options(opts, env):
  ("none", "custom", "debug", "speed", "speed_trace", "size"),
  )
  )
+ opts.Add(
+ EnumVariable(
+ "lto",
+ "Link-time optimization",
+ "none",
+ ("none", "auto", "thin", "full"),
+ )
+ )
  opts.Add(BoolVariable("debug_symbols", "Build with debugging symbols", True))
  opts.Add(BoolVariable("dev_build", "Developer build with dev-only debugging code (DEV_ENABLED)", False))
  opts.Add(BoolVariable("verbose", "Enable verbose output for the compilation", False))

tools/ios.py

@@ -97,4 +97,9 @@ def generate(env):
 
  env.Append(CPPDEFINES=["IOS_ENABLED", "UNIX_ENABLED"])
 
+ # Refer to https://github.com/godotengine/godot/blob/master/platform/ios/detect.py:
+ # Disable by default as it makes linking in Xcode very slow.
+ if env["lto"] == "auto":
+ env["lto"] = "none"
+
  common_compiler_flags.generate(env)

tools/linux.py

@@ -39,4 +39,8 @@ def generate(env):
 
  env.Append(CPPDEFINES=["LINUX_ENABLED", "UNIX_ENABLED"])
 
+ # Refer to https://github.com/godotengine/godot/blob/master/platform/linuxbsd/detect.py
+ if env["lto"] == "auto":
+ env["lto"] = "full"
+
  common_compiler_flags.generate(env)

tools/macos.py

@@ -73,4 +73,9 @@ def generate(env):
 
  env.Append(CPPDEFINES=["MACOS_ENABLED", "UNIX_ENABLED"])
 
+ # Refer to https://github.com/godotengine/godot/blob/master/platform/macos/detect.py
+ # LTO benefits for macOS (size, performance) haven't been clearly established yet.
+ if env["lto"] == "auto":
+ env["lto"] = "none"
+
  common_compiler_flags.generate(env)

tools/web.py

@@ -52,4 +52,8 @@ def generate(env):
 
  env.Append(CPPDEFINES=["WEB_ENABLED", "UNIX_ENABLED"])
 
+ # Refer to https://github.com/godotengine/godot/blob/master/platform/web/detect.py
+ if env["lto"] == "auto":
+ env["lto"] = "full"
+
  common_compiler_flags.generate(env)

tools/windows.py

@@ -198,4 +198,12 @@ def generate(env):
 
  env.Append(CPPDEFINES=["WINDOWS_ENABLED"])
 
+ # Refer to https://github.com/godotengine/godot/blob/master/platform/windows/detect.py
+ if env["lto"] == "auto":
+ if env.get("is_msvc", False):
+ # No LTO by default for MSVC, doesn't help.
+ env["lto"] = "none"
+ else: # Release
+ env["lto"] = "full"
+
  common_compiler_flags.generate(env)