From d5394d5f869eb5e440c2747cec9661cf1caf3bd0 Mon Sep 17 00:00:00 2001
From: NicoHood <git@nicohood.de>
Date: Wed, 23 Aug 2017 20:15:33 +0200
Subject: [PATCH] Added LTO

---
 DMBS/gcc.md |  4 ++++
 DMBS/gcc.mk | 11 ++++++++++-
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/DMBS/gcc.md b/DMBS/gcc.md
index d28fd9a..f7f3480 100644
--- a/DMBS/gcc.md
+++ b/DMBS/gcc.md
@@ -151,6 +151,10 @@ be assumed.
     <td>JUMP_TABLES</td>
     <td>Boolean, if `Y` jump tables will be enabled to slightly reduce the resulting binary's size - note that this can cause incorrect jumps if the binary is relocated after compilation, such as for a bootloader. Default is `N`.</td>
    </tr>
+   <tr>
+    <td>LTO</td>
+    <td>Boolean, if `Y` link time optimization will be enabled to reduce the resulting binary's size. For larger projects you might also want to add `-mcall-prologues` to the `CC_FLAGS`. Default is `N`.</td>
+   </tr>
    <tr>
     <td>OBJDIR</td>
     <td>Directory to store the intermediate object files, as they are generated from the source files. Default is `obj`.</td>
diff --git a/DMBS/gcc.mk b/DMBS/gcc.mk
index 35ff221..a811139 100644
--- a/DMBS/gcc.mk
+++ b/DMBS/gcc.mk
@@ -9,7 +9,9 @@
 DMBS_BUILD_MODULES         += GCC
 DMBS_BUILD_TARGETS         += size symbol-sizes all lib elf bin hex lss clean mostlyclean
 DMBS_BUILD_MANDATORY_VARS  += TARGET ARCH MCU SRC
-DMBS_BUILD_OPTIONAL_VARS   += COMPILER_PATH OPTIMIZATION C_STANDARD CPP_STANDARD F_CPU C_FLAGS CPP_FLAGS ASM_FLAGS CC_FLAGS LD_FLAGS OBJDIR OBJECT_FILES DEBUG_TYPE DEBUG_LEVEL LINKER_RELAXATIONS JUMP_TABLES
+DMBS_BUILD_OPTIONAL_VARS   += COMPILER_PATH OPTIMIZATION C_STANDARD CPP_STANDARD F_CPU C_FLAGS
+DMBS_BUILD_OPTIONAL_VARS   += CPP_FLAGS ASM_FLAGS CC_FLAGS LD_FLAGS OBJDIR OBJECT_FILES DEBUG_TYPE
+DMBS_BUILD_OPTIONAL_VARS   += DEBUG_LEVEL LINKER_RELAXATIONS JUMP_TABLES LTO
 DMBS_BUILD_PROVIDED_VARS   +=
 DMBS_BUILD_PROVIDED_MACROS +=
 
@@ -33,6 +35,7 @@ DEBUG_FORMAT       ?= dwarf-2
 DEBUG_LEVEL        ?= 2
 LINKER_RELAXATIONS ?= Y
 JUMP_TABLES        ?= N
+LTO                ?= N
 
 # Sanity check user supplied values
 $(foreach MANDATORY_VAR, $(DMBS_BUILD_MANDATORY_VARS), $(call ERROR_IF_UNSET, $(MANDATORY_VAR)))
@@ -47,6 +50,7 @@ $(call ERROR_IF_EMPTY, DEBUG_FORMAT)
 $(call ERROR_IF_EMPTY, DEBUG_LEVEL)
 $(call ERROR_IF_NONBOOL, LINKER_RELAXATIONS)
 $(call ERROR_IF_NONBOOL, JUMP_TABLES)
+$(call ERROR_IF_NONBOOL, LTO)
 
 # Determine the utility prefix to use for the selected architecture
 ifeq ($(ARCH), AVR8)
@@ -126,6 +130,11 @@ ifeq ($(JUMP_TABLES), N)
    # in a pseudo-random jump target.
    BASE_CC_FLAGS += -fno-jump-tables
 endif
+ifeq ($(LTO), Y)
+   # Enable link time optimization to reduce overall flash size.
+   BASE_CC_FLAGS += -flto -fuse-linker-plugin
+   BASE_LD_FLAGS += -flto -fuse-linker-plugin
+endif
 
 # Additional language specific compiler flags
 BASE_C_FLAGS   := -x c -O$(OPTIMIZATION) -std=$(C_STANDARD) -Wstrict-prototypes