--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/config/bootstrap-lto-lean.mk	Thu Feb 13 11:34:05 2020 +0900
@@ -0,0 +1,17 @@
+# This option enables LTO for stage4 and LTO for generators in stage3 with profiledbootstrap.
+# Otherwise, LTO is used in only stage3.
+
+STAGE3_CFLAGS += -flto=jobserver
+override STAGEtrain_CFLAGS := $(filter-out -flto=jobserver,$(STAGEtrain_CFLAGS))
+STAGEtrain_GENERATOR_CFLAGS += -flto=jobserver
+STAGEfeedback_CFLAGS += -flto=jobserver
+
+# assumes the host supports the linker plugin
+LTO_AR = $$r/$(HOST_SUBDIR)/prev-gcc/gcc-ar$(exeext) -B$$r/$(HOST_SUBDIR)/prev-gcc/
+LTO_RANLIB = $$r/$(HOST_SUBDIR)/prev-gcc/gcc-ranlib$(exeext) -B$$r/$(HOST_SUBDIR)/prev-gcc/
+
+LTO_EXPORTS = AR="$(LTO_AR)"; export AR; \
+	      RANLIB="$(LTO_RANLIB)"; export RANLIB;
+LTO_FLAGS_TO_PASS = AR="$(LTO_AR)" RANLIB="$(LTO_RANLIB)"
+
+do-compare = /bin/true