From 14da1424e0e8d96aee66676b8735001dbe6bd86b Mon Sep 17 00:00:00 2001
From: Shinichiro Hamaji <hamaji@google.com>
Date: Tue, 21 Jul 2015 07:28:39 +0900
Subject: [PATCH] Do not update previous_XXX.mk when there is no change

I'm adding a rule which regenerates ninja files to kati:

https://github.com/shinh/kati/commit/8666cfba20bf4ff0e59053dcfa7bcac9896bcf16

With this regeneration rule, unnecessary re-generation will happen
when these .mk files are updated even if there are no changes in
their contents. With this patch, these .mk files are updated only
when the contents will be actually changed.

Change-Id: I4c796f9454502f6bb25019b3806ca577ea5258c1
---
 core/cleanbuild.mk | 14 ++++++++++----
 core/post_clean.mk |  2 +-
 2 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/core/cleanbuild.mk b/core/cleanbuild.mk
index 938242ca8..c2386a423 100644
--- a/core/cleanbuild.mk
+++ b/core/cleanbuild.mk
@@ -105,11 +105,10 @@ else
   _crs_new_cmd :=
   steps :=
 endif
-CURRENT_CLEAN_BUILD_VERSION :=
-CURRENT_CLEAN_STEPS :=
 
 # Write the new state to the file.
 #
+ifneq ($(CURRENT_CLEAN_BUILD_VERSION)-$(CURRENT_CLEAN_STEPS),$(INTERNAL_CLEAN_BUILD_VERSION)-$(INTERNAL_CLEAN_STEPS))
 $(shell \
   mkdir -p $(dir $(clean_steps_file)) && \
   echo "CURRENT_CLEAN_BUILD_VERSION := $(INTERNAL_CLEAN_BUILD_VERSION)" > \
@@ -117,7 +116,10 @@ $(shell \
   echo "CURRENT_CLEAN_STEPS := $(INTERNAL_CLEAN_STEPS)" >> \
       $(clean_steps_file) \
  )
+endif
 
+CURRENT_CLEAN_BUILD_VERSION :=
+CURRENT_CLEAN_STEPS :=
 clean_steps_file :=
 INTERNAL_CLEAN_STEPS :=
 INTERNAL_CLEAN_BUILD_VERSION :=
@@ -164,7 +166,6 @@ ifdef PREVIOUS_BUILD_CONFIG
     endif
   endif
 endif  # else, this is the first build, so no need to clean.
-PREVIOUS_BUILD_CONFIG :=
 
 ifdef PREVIOUS_SANITIZE_TARGET
   ifneq "$(current_sanitize_target)" "$(PREVIOUS_SANITIZE_TARGET)"
@@ -172,10 +173,10 @@ ifdef PREVIOUS_SANITIZE_TARGET
     force_objclean := true
   endif
 endif  # else, this is the first build, so no need to clean.
-PREVIOUS_SANITIZE_TARGET :=
 
 # Write the new state to the file.
 #
+ifneq ($(PREVIOUS_BUILD_CONFIG)-$(PREVIOUS_SANITIZE_TARGET),$(current_build_config)-$(current_sanitize_target))
 $(shell \
   mkdir -p $(dir $(previous_build_config_file)) && \
   echo "PREVIOUS_BUILD_CONFIG := $(current_build_config)" > \
@@ -183,6 +184,9 @@ $(shell \
   echo "PREVIOUS_SANITIZE_TARGET := $(current_sanitize_target)" >> \
       $(previous_build_config_file) \
  )
+endif
+PREVIOUS_BUILD_CONFIG :=
+PREVIOUS_SANITIZE_TARGET :=
 previous_build_config_file :=
 current_build_config :=
 
@@ -305,10 +309,12 @@ endif
 endif # else, this is the first build, so no need to clean.
 
 # Write the new state to the file.
+ifneq ($(PREVIOUS_PREBUILT_TOOLS),$(current_prebuilt_tools))
 $(shell \
   mkdir -p $(dir $(previous_prebuilt_tools_config_file)) && \
   echo "PREVIOUS_PREBUILT_TOOLS:=$(current_prebuilt_tools)" > \
     $(previous_prebuilt_tools_config_file))
+endif
 
 ifeq ($(force_tools_clean),true)
 # For this list of prebuilt tools, see prebuilts/sdk/tools/Android.mk.
diff --git a/core/post_clean.mk b/core/post_clean.mk
index 0273ff207..7fafe4a5e 100644
--- a/core/post_clean.mk
+++ b/core/post_clean.mk
@@ -88,7 +88,7 @@ MODULES_WITH_AIDL_FILES := $(sort $(MODULES_WITH_AIDL_FILES) $(modules_with_aidl
 $(shell echo 'MODULES_WITH_AIDL_FILES := $(MODULES_WITH_AIDL_FILES)' >> $(current_aidl_config))
 
 # Now current becomes previous.
-$(shell mv -f $(current_aidl_config) $(previous_aidl_config))
+$(shell cmp $(current_aidl_config) $(previous_aidl_config) > /dev/null 2>&1 || mv -f $(current_aidl_config) $(previous_aidl_config))
 
 MODULES_WITH_AIDL_FILES :=
 modules_with_aidl_files :=
-- 
2.11.0