build: add CONFIG_LTO to enable link-time optimization

Change-Id: I9546d715b8d2ca3ebf46183bdbaa58e8aa921d95
Signed-off-by: Daniel Verkamp <daniel.verkamp@intel.com>
Signed-off-by: Ben Walker <benjamin.walker@intel.com>

.gitignore

@@ -23,3 +23,4 @@ CONFIG.local
 .project
 .cproject
 .settings
+mk/cc.mk

CONFIG

@@ -37,6 +37,9 @@ CONFIG_DEBUG?=n
 # Treat warnings as errors (fail the build on any warning).
 CONFIG_WERROR?=n
 
+# Build with link-time optimization.
+CONFIG_LTO?=n
+
 # Build with code coverage instrumentation.
 CONFIG_COVERAGE?=n
 

Makefile

@@ -38,17 +38,23 @@ include $(SPDK_ROOT_DIR)/mk/spdk.common.mk
 
 DIRS-y += lib test examples app
 
-.PHONY: all clean $(DIRS-y) config.h CONFIG.local
+.PHONY: all clean $(DIRS-y) config.h CONFIG.local mk/cc.mk
 
 all: $(DIRS-y)
 clean: $(DIRS-y)
+	$(Q)rm -f mk/cc.mk
 	$(Q)rm -f config.h
 
 app: lib
 test: lib
 examples: lib
 
-$(DIRS-y): config.h
+$(DIRS-y): mk/cc.mk config.h
+
+mk/cc.mk:
+	$(Q)scripts/detect_cc.sh --cc=$(CC) --cxx=$(CXX) --lto=$(CONFIG_LTO) > $@.tmp; \
+	cmp -s $@.tmp $@ || mv $@.tmp $@ ; \
+	rm -f $@.tmp
 
 config.h: CONFIG CONFIG.local scripts/genconfig.py
 	$(Q)python scripts/genconfig.py $(MAKEFLAGS) > $@.tmp; \

configure

@@ -17,6 +17,7 @@ function usage()
 	echo " --enable-asan             Enable address sanitizer"
 	echo " --enable-ubsan            Enable undefined behavior sanitizer"
 	echo " --enable-coverage         Enable code coverage tracking"
+	echo " --enable-lto              Enable link-time optimization"
 	echo " --with-env=path           Use an alternate environment implementation"
 	echo ""
 	echo "Specifying Dependencies:"
@@ -67,6 +68,12 @@ for i in "$@"; do
 		--disable-coverage)
 			CONFIG_COVERAGE=n
 			;;
+		--enable-lto)
+			CONFIG_LTO=y
+			;;
+		--disable-lto)
+			CONFIG_LTO=n
+			;;
 		--enable-werror)
 			CONFIG_WERROR=y
 			;;
@@ -139,6 +146,9 @@ fi
 if [ -n "$CONFIG_COVERAGE" ]; then
 	echo "CONFIG_COVERAGE?=$CONFIG_COVERAGE" >> CONFIG.local
 fi
+if [ -n "$CONFIG_LTO" ]; then
+	echo "CONFIG_LTO?=$CONFIG_LTO" >> CONFIG.local
+fi
 if [ -n "$CONFIG_ASAN" ]; then
 	echo "CONFIG_ASAN?=$CONFIG_ASAN" >> CONFIG.local
 fi

mk/spdk.common.mk

@@ -34,6 +34,8 @@
 -include $(SPDK_ROOT_DIR)/CONFIG.local
 include $(SPDK_ROOT_DIR)/CONFIG
 
+-include $(SPDK_ROOT_DIR)/mk/cc.mk
+
 C_OPT ?= -fno-omit-frame-pointer
 ifneq ($(V),1)
 Q ?= @
@@ -54,6 +56,11 @@ ifeq ($(CONFIG_WERROR), y)
 COMMON_CFLAGS += -Werror
 endif
 
+ifeq ($(CONFIG_LTO),y)
+COMMON_CFLAGS += -flto
+LDFLAGS += -flto
+endif
+
 COMMON_CFLAGS += -Wformat -Wformat-security
 
 COMMON_CFLAGS += -D_GNU_SOURCE
@@ -149,7 +156,7 @@ LINK_CXX=\
 LIB_C=\
 	$(Q)echo "  LIB $(notdir $@)"; \
 	rm -f $@; \
-	ar crDs $@ $(OBJS)
+	$(CCAR) crDs $@ $(OBJS)
 
 # Clean up generated files listed as arguments plus a default list
 CLEAN_C=\

scripts/detect_cc.sh

@@ -0,0 +1,80 @@
+#!/usr/bin/env bash
+
+set -e
+
+function err()
+{
+        echo "$@" >&2
+}
+
+function usage()
+{
+	err "Detect compiler and linker versions, generate mk/cc.mk"
+	err ""
+	err "Usage: ./detect_cc.sh [OPTION]..."
+	err ""
+	err "Defaults for the options are specified in brackets."
+	err ""
+	err "General:"
+	err " -h, --help                Display this help and exit"
+	err " --cc=path                 C compiler to use"
+	err " --cxx=path                C++ compiler to use"
+        err " --lto=[y|n]               Attempt to configure for LTO"
+
+}
+
+CC=cc
+CXX=c++
+LTO=n
+
+for i in "$@"; do
+	case "$i" in
+		-h|--help)
+			usage
+			exit 0
+			;;
+		--cc=*)
+			CC="${i#*=}"
+			;;
+		--cxx=*)
+			CXX="${i#*=}"
+			;;
+		--lto=*)
+			LTO="${i#*=}"
+			;;
+		--)
+			break
+			;;
+		*)
+			err "Unrecognized option $i"
+			usage
+			exit 1
+	esac
+done
+
+CC_TYPE=$($CC -v 2>&1 | grep version | awk '{print $1}')
+CXX_TYPE=$($CXX -v 2>&1 | grep version | awk '{print $1}')
+LD_TYPE=$(ld -v 2>&1 | awk '{print $2}')
+
+if [ "$CC_TYPE" != "$CXX_TYPE" ]; then
+        err "C compiler is $CC_TYPE but C++ compiler is $CXX_TYPE"
+        err "This may result in errors"
+        exit 1
+fi
+
+CCAR="ar"
+if [ "$LTO" = "y" ]; then
+        if [ "$CC_TYPE" = "clang" ]; then
+                if [ "$LD_TYPE" != "gold" ]; then
+                        err "Using LTO with clang requires the gold linker."
+                        exit 1
+                fi
+                CCAR="llvm-ar"
+        else
+                CCAR="gcc-ar"
+        fi
+fi
+
+echo "CC=$CC"
+echo "CXX=$CXX"
+echo "CCAR=$CCAR"