Makefile: evaluate LDFLAGS_BUILD_ID only once

Evaluate LDFLAGS_BUILD_ID (which involves invoking the compiler) only
once instead of over and over.

This provides a ~20% reduction in null build time with x86 allnoconfig:

$ make allnoconfig && make -j8
$ perf stat -r5 -e sched:sched_process_exec make -j8
-       2 119      sched:sched_process_exec
+       1 878      sched:sched_process_exec

-       1,238817018 seconds time elapsed
+       0,971020553 seconds time elapsed

Signed-off-by: Rabin Vincent <rabin@rab.in>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

diff --git a/Makefile b/Makefile
index 10d6cd348abb3ffa284ca769849181e270e1644b..35497e93399582b56b8ec1818fe722451d6de548 100644 (file)
--- a/Makefile
+++ b/Makefile
@@ -829,7 +829,7 @@ KBUILD_AFLAGS   += $(ARCH_AFLAGS)   $(KAFLAGS)
 KBUILD_CFLAGS   += $(ARCH_CFLAGS)   $(KCFLAGS)
 
 # Use --build-id when available.
-LDFLAGS_BUILD_ID = $(patsubst -Wl$(comma)%,%,\
+LDFLAGS_BUILD_ID := $(patsubst -Wl$(comma)%,%,\
                              $(call cc-ldoption, -Wl$(comma)--build-id,))
 KBUILD_LDFLAGS_MODULE += $(LDFLAGS_BUILD_ID)
 LDFLAGS_vmlinux += $(LDFLAGS_BUILD_ID)