linux-kernel - Re: [PATCH 3/4] m68k: optimize cc-option calls for cpuflags-y

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Date:   Wed, 27 May 2020 22:55:47 +1000
From:   Greg Ungerer <gerg@...ux-m68k.org>
To:     Masahiro Yamada <masahiroy@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        linux-m68k@...ts.linux-m68k.org
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] m68k: optimize cc-option calls for cpuflags-y


On 26/5/20 10:38 pm, Masahiro Yamada wrote:
> arch/m68k/Makefile computes lots of unneeded cc-option calls.
> 
> For example, if CONFIG_M5441x is not defined, there is not point in
> evaluating the following compiler flag.
> 
>   cpuflags-$(CONFIG_M5441x)      := $(call cc-option,-mcpu=54455,-mcfv4e)
> 
> The result is set to cpuflags-, then thrown away.
> 
> The right hand side of ':=' is immediately expanded. Hence, all of the
> 16 calls for cc-option are evaluated. This is expensive since cc-option
> invokes the compiler. This occurs even if you are not attempting to
> build anything, like 'make ARCH=m68k help'.
> 
> Use '=' to expand the value _lazily_. The evaluation for cc-option is
> delayed until $(cpuflags-y) is expanded. So, the cc-option test happens
> just once at most.
> 
> This commit mimics tune-y of arch/arm/Makefile.
> 
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>

Acked-by: Greg Ungerer <gerg@...ux-m68k.org>

Regards
Greg


> ---
> 
>   arch/m68k/Makefile | 45 ++++++++++++++++++++++++---------------------
>   1 file changed, 24 insertions(+), 21 deletions(-)
> 
> diff --git a/arch/m68k/Makefile b/arch/m68k/Makefile
> index 88d4d8bbecd6..ae6e29da3a3e 100644
> --- a/arch/m68k/Makefile
> +++ b/arch/m68k/Makefile
> @@ -32,30 +32,33 @@ endif
>   #	compiler cpu type flag.
>   #
>   ifndef CONFIG_M68040
> -cpuflags-$(CONFIG_M68060)	:= -m68060
> +cpuflags-$(CONFIG_M68060)	= -m68060
>   endif
>   ifndef CONFIG_M68060
> -cpuflags-$(CONFIG_M68040)	:= -m68040
> +cpuflags-$(CONFIG_M68040)	= -m68040
>   endif
> -cpuflags-$(CONFIG_M68030)	:=
> -cpuflags-$(CONFIG_M68020)	:=
> -cpuflags-$(CONFIG_M68000)	:= -m68000
> -cpuflags-$(CONFIG_M5441x)	:= $(call cc-option,-mcpu=54455,-mcfv4e)
> -cpuflags-$(CONFIG_M54xx)	:= $(call cc-option,-mcpu=5475,-m5200)
> -cpuflags-$(CONFIG_M5407)	:= $(call cc-option,-mcpu=5407,-m5200)
> -cpuflags-$(CONFIG_M532x)	:= $(call cc-option,-mcpu=532x,-m5307)
> -cpuflags-$(CONFIG_M537x)	:= $(call cc-option,-mcpu=537x,-m5307)
> -cpuflags-$(CONFIG_M5307)	:= $(call cc-option,-mcpu=5307,-m5200)
> -cpuflags-$(CONFIG_M528x)	:= $(call cc-option,-mcpu=528x,-m5307)
> -cpuflags-$(CONFIG_M5275)	:= $(call cc-option,-mcpu=5275,-m5307)
> -cpuflags-$(CONFIG_M5272)	:= $(call cc-option,-mcpu=5272,-m5307)
> -cpuflags-$(CONFIG_M5271)	:= $(call cc-option,-mcpu=5271,-m5307)
> -cpuflags-$(CONFIG_M523x)	:= $(call cc-option,-mcpu=523x,-m5307)
> -cpuflags-$(CONFIG_M525x)	:= $(call cc-option,-mcpu=5253,-m5200)
> -cpuflags-$(CONFIG_M5249)	:= $(call cc-option,-mcpu=5249,-m5200)
> -cpuflags-$(CONFIG_M520x)	:= $(call cc-option,-mcpu=5208,-m5200)
> -cpuflags-$(CONFIG_M5206e)	:= $(call cc-option,-mcpu=5206e,-m5200)
> -cpuflags-$(CONFIG_M5206)	:= $(call cc-option,-mcpu=5206,-m5200)
> +cpuflags-$(CONFIG_M68030)	=
> +cpuflags-$(CONFIG_M68020)	=
> +cpuflags-$(CONFIG_M68000)	= -m68000
> +cpuflags-$(CONFIG_M5441x)	= $(call cc-option,-mcpu=54455,-mcfv4e)
> +cpuflags-$(CONFIG_M54xx)	= $(call cc-option,-mcpu=5475,-m5200)
> +cpuflags-$(CONFIG_M5407)	= $(call cc-option,-mcpu=5407,-m5200)
> +cpuflags-$(CONFIG_M532x)	= $(call cc-option,-mcpu=532x,-m5307)
> +cpuflags-$(CONFIG_M537x)	= $(call cc-option,-mcpu=537x,-m5307)
> +cpuflags-$(CONFIG_M5307)	= $(call cc-option,-mcpu=5307,-m5200)
> +cpuflags-$(CONFIG_M528x)	= $(call cc-option,-mcpu=528x,-m5307)
> +cpuflags-$(CONFIG_M5275)	= $(call cc-option,-mcpu=5275,-m5307)
> +cpuflags-$(CONFIG_M5272)	= $(call cc-option,-mcpu=5272,-m5307)
> +cpuflags-$(CONFIG_M5271)	= $(call cc-option,-mcpu=5271,-m5307)
> +cpuflags-$(CONFIG_M523x)	= $(call cc-option,-mcpu=523x,-m5307)
> +cpuflags-$(CONFIG_M525x)	= $(call cc-option,-mcpu=5253,-m5200)
> +cpuflags-$(CONFIG_M5249)	= $(call cc-option,-mcpu=5249,-m5200)
> +cpuflags-$(CONFIG_M520x)	= $(call cc-option,-mcpu=5208,-m5200)
> +cpuflags-$(CONFIG_M5206e)	= $(call cc-option,-mcpu=5206e,-m5200)
> +cpuflags-$(CONFIG_M5206)	= $(call cc-option,-mcpu=5206,-m5200)
> +
> +# Evaluate tune cc-option calls now
> +cpuflags-y := $(cpuflags-y)
>   
>   KBUILD_AFLAGS += $(cpuflags-y)
>   KBUILD_CFLAGS += $(cpuflags-y)
>