Merge pull request #253 from sysprog21/enable-lto

Enable link-time optimization by default

Author: jserv

Makefile

@@ -16,6 +16,28 @@ CFLAGS += -D DEFAULT_STACK_ADDR=0xFFFFE000
 # Set the default args starting address
 CFLAGS += -D DEFAULT_ARGS_ADDR=0xFFFFF000
 
+# Enable link-time optimization (LTO)
+ENABLE_LTO ?= 1
+ifeq ($(call has, LTO), 1)
+ifeq ("$(CC_IS_CLANG)$(CC_IS_GCC)",)
+$(warning LTO is only supported in clang and gcc.)
+override ENABLE_LTO := 0
+endif
+endif
+$(call set-feature, LTO)
+ifeq ($(call has, LTO), 1)
+ifeq ("$(CC_IS_GCC)", "1")
+CFLAGS += -flto
+endif
+ifeq ("$(CC_IS_CLANG)", "1")
+CFLAGS += -flto=thin -fsplit-lto-unit
+LDFLAGS += -flto=thin
+endif
+endif
+
+# Disable Intel's Control-flow Enforcement Technology (CET)
+CFLAGS += $(CFLAGS_NO_CET)
+
 OBJS_EXT :=
 
 # Control and Status Register (CSR)
@@ -90,7 +112,7 @@ endif
 
 # For tail-call elimination, we need a specific set of build flags applied.
 # FIXME: On macOS + Apple Silicon, -fno-stack-protector might have a negative impact.
-$(OUT)/emulate.o: CFLAGS += $(CFLAGS_NO_CET) -foptimize-sibling-calls -fomit-frame-pointer -fno-stack-check -fno-stack-protector
+$(OUT)/emulate.o: CFLAGS += -foptimize-sibling-calls -fomit-frame-pointer -fno-stack-check -fno-stack-protector
 
 # Clear the .DEFAULT_GOAL special variable, so that the following turns
 # to the first target after .DEFAULT_GOAL is not set.