linux-kernel - [PATCH 4/4] Makefile: lld: set -O2 linker flag when linking with LLD

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Date:   Thu,  7 Feb 2019 14:01:52 -0800
From:   ndesaulniers@...gle.com
To:     yamada.masahiro@...ionext.com
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Rui Ueyama <ruiu@...gle.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 4/4] Makefile: lld: set -O2 linker flag when linking with LLD

-O2 enables tail merging of string table strings.

For arm64:
0.34% size improvement with lld -O2 over lld for vmlinux.
3.30% size improvement with lld -O2 over lld for Image.lz4-dtb.

Link: https://github.com/ClangBuiltLinux/linux/issues/343
Suggested-by: Rui Ueyama <ruiu@...gle.com>
Suggested-by: Nathan Chancellor <natechancellor@...il.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
---
 Makefile | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/Makefile b/Makefile
index 6307c17259ea..c07208ec49d4 100644
--- a/Makefile
+++ b/Makefile
@@ -718,6 +718,10 @@ else
 KBUILD_CFLAGS += -Wno-unused-but-set-variable
 endif
 
+ifdef CONFIG_LD_IS_LLD
+KBUILD_LDFLAGS += -O2
+endif
+
 KBUILD_CFLAGS += $(call cc-disable-warning, unused-const-variable)
 ifdef CONFIG_FRAME_POINTER
 KBUILD_CFLAGS	+= -fno-omit-frame-pointer -fno-optimize-sibling-calls
-- 
2.20.1.791.gb4d0f1c61a-goog