[U-Boot] [PATCH v3] config.mk: use memoization in cc-option macro to speed up compilation

[Daniel Schwierzeck]

Apply memoization to cc-option macro by caching the results of the
gcc calls. This macro is called very often so using cached results
leads to faster compilation times.

The old behaviour can be restored by defining the config option
CONFIG_CC_OPT_CACHE_DISABLE=y.

Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck at googlemail.com>
---
Changes for v3:
 - reworked handling of non-working gcc options
 - add config option CONFIG_CC_OPT_CACHE_DISABLE

Changes for v2:
 - move cache file to $(obj)/include/generated
 - reworked completely
 - cache also non-working gcc options
 - remove CACHE_CC_OPTIONS config switch and enable this optimization
   by default

 config.mk |   20 ++++++++++++++++++--
 1 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/config.mk b/config.mk
index 918cffe..ddaa477 100644
--- a/config.mk
+++ b/config.mk
@@ -107,8 +107,24 @@ HOSTCFLAGS	+= -pedantic
 # Option checker (courtesy linux kernel) to ensure
 # only supported compiler options are used
 #
-cc-option = $(shell if $(CC) $(CFLAGS) $(1) -S -o /dev/null -xc /dev/null \
-		> /dev/null 2>&1; then echo "$(1)"; else echo "$(2)"; fi ;)
+CC_OPTIONS_CACHE_FILE := $(OBJTREE)/include/generated/cc_options.mk
+
+$(if $(wildcard $(CC_OPTIONS_CACHE_FILE)),,\
+	$(shell mkdir -p $(dir $(CC_OPTIONS_CACHE_FILE))))
+
+-include $(CC_OPTIONS_CACHE_FILE)
+
+cc-option-sys = $(shell if $(CC) $(CFLAGS) $(1) -S -o /dev/null -xc /dev/null \
+		> /dev/null 2>&1; then \
+		echo 'CC_OPTIONS += $(strip $1)' >> $(CC_OPTIONS_CACHE_FILE); \
+		echo "$(1)"; fi)
+
+ifeq ($(CONFIG_CC_OPT_CACHE_DISABLE),y)
+cc-option = $(strip $(if $(call cc-option-sys,$1),$1,$2))
+else
+cc-option = $(strip $(if $(findstring $1,$(CC_OPTIONS)),$1,\
+		$(if $(call cc-option-sys,$1),$1,$2)))
+endif
 
 #
 # Include the make variables (CC, etc...)
-- 
1.7.7.1