[U-Boot] [PATCH v2] 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.

Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck at googlemail.com>
---
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 |   23 +++++++++++++++++++++--
 1 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/config.mk b/config.mk
index 918cffe..0da961a 100644
--- a/config.mk
+++ b/config.mk
@@ -107,8 +107,27 @@ 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))))
+
+sinclude $(CC_OPTIONS_CACHE_FILE)
+
+_ccopt_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)"; else \
+		[ "x$(strip $2)" != "x" ] && \
+			echo 'CC_OPTIONS_NOP += $(strip $2)' >> $(CC_OPTIONS_CACHE_FILE); \
+		echo "$(2)"; fi)
+
+_ccopt_cached = $(if $(filter $1,$(CC_OPTIONS)),$1,)
+_ccopt_nop_cached = $(if $(filter $1,$(CC_OPTIONS_NOP)),$1,)
+
+cc-option = $(if $(call _ccopt_cached,$1),$1,\
+		$(if $(call _ccopt_nop_cached,$2),$2,\
+		$(call _ccopt_sys,$1,$2)))
 
 #
 # Include the make variables (CC, etc...)
-- 
1.7.7.1