From d6b847db0d41202104db6e218a0addd794a6097c Mon Sep 17 00:00:00 2001
From: Kai Krakow <kai@kaishome.de>
Date: Tue, 16 Jan 2018 01:02:57 +0100
Subject: [PATCH] Makefile: speedup dependency generation

Dependencies can be generated in parallel which can be much faster. It
also puts away the problem that for may fail multiple times in a row and
leaving behind a broken intermediate file which would be picked up by
successive runs.

Signed-off-by: Kai Krakow <kai@kaishome.de>
---
 .gitignore    |  1 +
 lib/Makefile  |  8 ++++++--
 src/Makefile  | 43 +++++++++++++++++++++++--------------------
 test/Makefile | 10 +++++++---
 4 files changed, 37 insertions(+), 25 deletions(-)

diff --git a/.gitignore b/.gitignore
index e00f61d..72e65cb 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,6 +1,7 @@
 *.[ao]
 *.bak
 *.new
+*.dep
 *.so*
 Doxyfile
 README.html
diff --git a/lib/Makefile b/lib/Makefile
index 6db5122..ae8392f 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -24,8 +24,12 @@ libcrucible.so: $(CRUCIBLE_OBJS)
 
 include ../makeflags
 
-depends.mk: *.cc
-	for x in $^; do $(CXX) $(CXXFLAGS) -M -MG -MT "$${x/%.cc/.o}" "$$x"; done > $@.new
+.depends/%.dep: %.cc Makefile
+	@mkdir -p .depends
+	$(CXX) $(CXXFLAGS) -M -MF $@ -MT $(<:.cc=.o) $<
+
+depends.mk: $(CRUCIBLE_OBJS:%.o=.depends/%.dep)
+	cat $^ > $@.new
 	mv -f $@.new $@
 
 .version.cc: Makefile ../makeflags *.cc ../include/crucible/*.h
diff --git a/src/Makefile b/src/Makefile
index c720c6a..d6ccb25 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -10,23 +10,6 @@ include ../makeflags
 LIBS = -lcrucible -lpthread
 LDFLAGS = -L../lib
 
-depends.mk: Makefile *.cc
-	for x in *.cc; do $(CXX) $(CXXFLAGS) -M "$$x"; done > depends.mk.new
-	mv -fv depends.mk.new depends.mk
-
-bees-version.c: Makefile *.cc *.h
-	echo "const char *BEES_VERSION = \"$(shell git describe --always --dirty || echo UNKNOWN)\";" > bees-version.new.c
-	mv -f bees-version.new.c bees-version.c
-
-include depends.mk
-
-%.o: %.cc %.h
-	$(CXX) $(CXXFLAGS) -o "$@" -c "$<"
-
-../bin/%: %.o
-	@echo Implicit bin rule "$<" '->' "$@"
-	$(CXX) $(CXXFLAGS) -o "$@" "$<" $(LDFLAGS) $(LIBS)
-
 BEES_OBJS = \
 	bees.o \
 	bees-context.o \
@@ -35,10 +18,30 @@ BEES_OBJS = \
 	bees-roots.o \
 	bees-thread.o \
 	bees-types.o \
-	bees-version.o \
 
-../bin/bees: $(BEES_OBJS)
-	$(CXX) $(CXXFLAGS) -o "$@" $(BEES_OBJS) $(LDFLAGS) $(LIBS)
+bees-version.c: bees.h $(BEES_OBJS:.o=.cc) Makefile
+	echo "const char *BEES_VERSION = \"$(shell git describe --always --dirty || echo UNKNOWN)\";" > bees-version.new.c
+	mv -f bees-version.new.c bees-version.c
+
+.depends/%.dep: %.cc Makefile
+	@mkdir -p .depends
+	$(CXX) $(CXXFLAGS) -M -MF $@ -MT $(<:.cc=.o) $<
+
+depends.mk: $(BEES_OBJS:%.o=.depends/%.dep)
+	cat $^ > $@.new
+	mv -f $@.new $@
+
+include depends.mk
+
+%.o: %.cc %.h
+	$(CXX) $(CXXFLAGS) -o "$@" -c "$<"
+
+../bin/%: %.o
+	@echo Implicit bin rule "$<" '->' "$@"
+	$(CXX) $(CXXFLAGS) $(LDFLAGS) $(LIBS) -o $@ $<
+
+../bin/bees: $(BEES_OBJS) bees-version.o
+	$(CXX) $(CXXFLAGS) -o "$@" $^ $(LDFLAGS) $(LIBS)
 
 clean:
 	-rm -fv bees-version.h
diff --git a/test/Makefile b/test/Makefile
index 532f617..13e6f21 100644
--- a/test/Makefile
+++ b/test/Makefile
@@ -17,9 +17,13 @@ include ../makeflags
 LIBS = -lcrucible -lpthread
 LDFLAGS = -L../lib -Wl,-rpath=$(shell realpath ../lib)
 
-depends.mk: *.cc
-	for x in *.cc; do $(CXX) $(CXXFLAGS) -M "$$x"; done > depends.mk.new
-	mv -fv depends.mk.new depends.mk
+.depends/%.dep: %.cc
+	@mkdir -p .depends
+	$(CXX) $(CXXFLAGS) -M -MF $@ -MT $(<:.cc=.o) $<
+
+depends.mk: $(PROGRAMS:%=.depends/%.dep)
+	cat $^ > $@.new
+	mv -f $@.new $@
 
 include depends.mk