linux-kernel - Re: [PATCH v2 4/4] Makefile: lld: set -O2 linker flag when linking with LLD

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Message-ID: <20190212122221.GF32494@hirez.programming.kicks-ass.net>
Date:   Tue, 12 Feb 2019 13:22:21 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     ndesaulniers@...gle.com
Cc:     yamada.masahiro@...ionext.com, natechancellor@...il.com,
        sedat.dilek@...il.com, keescook@...omium.org,
        samitolvanen@...gle.com, michal.lkml@...kovi.net,
        akpm@...ux-foundation.org, hannes@...xchg.org,
        linux@...inikbrodowski.net, npiggin@...il.com,
        mathieu.desnoyers@...icios.com, gor@...ux.ibm.com, adrian@...as.de,
        rgb@...hat.com, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org, Rui Ueyama <ruiu@...gle.com>
Subject: Re: [PATCH v2 4/4] Makefile: lld: set -O2 linker flag when linking
 with LLD

On Mon, Feb 11, 2019 at 11:30:06AM -0800, ndesaulniers@...gle.com wrote:
> For arm64:
> 0.34% size improvement with lld -O2 over lld for vmlinux.
> 3.3% size improvement with lld -O2 over lld for Image.lz4-dtb.

The Changelog is utterly failing to explain what it does.

> Link: https://github.com/ClangBuiltLinux/linux/issues/343

That is irrelevant crap.

> Suggested-by: Rui Ueyama <ruiu@...gle.com>
> Suggested-by: Nathan Chancellor <natechancellor@...il.com>
> Reviewed-by: Nathan Chancellor <natechancellor@...il.com>
> Tested-by: Nathan Chancellor <natechancellor@...il.com>
> Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
> ---
> Changes V1->V2:
> * add tested and reviewed by tags.
> 
>  Makefile | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/Makefile b/Makefile
> index 00e8e01d23fc..8011555745aa 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
>