commit bd74370b8657fc6fdab7b0d5024d011985183809
author Rabin Vincent <rabin@rab.in> Sun Apr 30 18:16:00 2017 +0200
committer Masahiro Yamada <yamada.masahiro@socionext.com> Wed May 03 13:43:24 2017 +0900
tree c56e46863c2140258cb93768fd19adbee3f68c8c
parent e8a3118e1f5cbe0c26704419390bf074689b349f

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>

Makefile

diff --git a/Makefile b/Makefile
index 10d6cd3..35497e9 100644
--- a/Makefile
+++ b/Makefile
@@ -829,7 +829,7 @@
 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)