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Subject[PATCH 3/4] m68k: optimize cc-option calls for cpuflags-y
Date
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@kernel.org>
---

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)
--
2.25.1
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