[PATCH 10/12] Makefile: lazily compute header dependencies
- From
Jonathan Nieder <jrnieder@gmail.com>
- Date
- Jan 26, 2010, 15:52 UTC
- Message-ID
- <20100126155249.GK4895@progeny.tock>
- In-Reply-To
- <20100126154357.GA4895@progeny.tock>
Use the gcc -MMD -MP -MF options to generate dependency rules as a byproduct when building .o files if the COMPUTE_HEADER_DEPENDENCIES variable is defined. That variable is left undefined by default for now.
As each object file is built, write a makefile fragment containing its dependencies in the deps/ subdirectory of its containing directory. The deps/ directories should be generated if they are missing at the start of each build. So let each object file depend on $(missing_dep_dirs), which lists only the directories of this kind that are missing to avoid needlessly regenerating files when the directories' timestamps change.
gcc learned the -MMD -MP -MF options in version 3.0, so most gcc users should have them by now.
The dependencies this option computes are more specific than the rough estimates hard-coded in the Makefile, greatly speeding up rebuilds when only a little-used header file has changed.
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com> --- .gitignore | 1 + Makefile | 49 ++++++++++++++++++++++++++++++++++++++++++++----- 2 files changed, 45 insertions(+), 5 deletions(-)
diff --git a/.gitignore b/.gitignore index 8df8f88..7b3acb7 100644 --- a/.gitignore +++ b/.gitignore @@ -177,6 +177,7 @@ *.exe *.[aos] *.py[co] +*.o.d *+ /config.mak /autom4te.cache diff --git a/Makefile b/Makefile index 0e4e8ff..2e75f05 100644 --- a/Makefile +++ b/Makefile @@ -217,6 +217,10 @@ all:: # DEFAULT_EDITOR='~/bin/vi', # DEFAULT_EDITOR='$GIT_FALLBACK_EDITOR', # DEFAULT_EDITOR='"C:\Program Files\Vim\gvim.exe" --nofork' +# +# Define COMPUTE_HEADER_DEPENDENCIES if your compiler supports the -MMD option +# and you want to avoid rebuilding objects when an unrelated header file +# changes. GIT-VERSION-FILE: FORCE @$(SHELL_PATH) ./GIT-VERSION-GEN @@ -1677,14 +1681,48 @@ ASM_SRC := $(wildcard $(OBJECTS:o=S)) ASM_OBJ := $(ASM_SRC:S=o) C_OBJ := $(filter-out $(ASM_OBJ),$(OBJECTS)) +ifdef COMPUTE_HEADER_DEPENDENCIES +dep_dirs := $(addsuffix deps,$(sort $(dir $(OBJECTS)))) +$(dep_dirs): + mkdir -p $@ + +missing_dep_dirs := $(filter-out $(wildcard $(dep_dirs)),$(dep_dirs)) +else +dep_dirs = +missing_dep_dirs = +endif + .SUFFIXES: -$(C_OBJ): %.o: %.c GIT-CFLAGS - $(QUIET_CC)$(CC) -o $*.o -c $(ALL_CFLAGS) $< +$(C_OBJ): %.o: %.c GIT-CFLAGS $(missing_dep_dirs) + $(QUIET_CC)$(CC) -o $*.o -c $(dep_args) $(ALL_CFLAGS) $< %.s: %.c GIT-CFLAGS FORCE $(QUIET_CC)$(CC) -S $(ALL_CFLAGS) $< -$(ASM_OBJ): %.o: %.S GIT-CFLAGS - $(QUIET_CC)$(CC) -o $*.o -c $(ALL_CFLAGS) $< +$(ASM_OBJ): %.o: %.S GIT-CFLAGS $(missing_dep_dirs) + $(QUIET_CC)$(CC) -o $*.o -c $(dep_args) $(ALL_CFLAGS) $< + +ifdef COMPUTE_HEADER_DEPENDENCIES +# Take advantage of gcc's on-the-fly dependency generation +# See <http://gcc.gnu.org/gcc-3.0/features.html>. +dep_files := $(wildcard $(foreach f,$(OBJECTS),$(dir f)deps/$(notdir $f).d)) +ifneq ($(dep_files),) +include $(dep_files) +endif + +dep_file = $(dir $@)deps/$(notdir $@).d +dep_args = -MF $(dep_file) -MMD -MP +else +dep_args = + +# Dependencies on header files, for platforms that do not support +# the gcc -MMD option. +# +# Dependencies on automatically generated headers such as common-cmds.h +# should _not_ be included here, since they are necessary even when +# building an object for the first time. +# +# XXX. Please check occasionally that these include all dependencies +# gcc detects! $(GIT_OBJS): $(LIB_H) builtin-branch.o builtin-checkout.o builtin-clone.o builtin-reset.o branch.o transport.o: branch.h @@ -1700,10 +1738,10 @@ builtin-pack-objects.o: thread-utils.h http-fetch.o http-walker.o remote-curl.o transport.o walker.o: walker.h http.o http-walker.o http-push.o remote-curl.o: http.h - xdiff-interface.o $(XDIFF_OBJS): \ xdiff/xinclude.h xdiff/xmacros.h xdiff/xdiff.h xdiff/xtypes.h \ xdiff/xutils.h xdiff/xprepare.h xdiff/xdiffi.h xdiff/xemit.h +endif exec_cmd.s exec_cmd.o: ALL_CFLAGS += \ '-DGIT_EXEC_PATH="$(gitexecdir_SQ)"' \ @@ -2011,6 +2049,7 @@ clean: $(RM) $(ALL_PROGRAMS) $(BUILT_INS) git$X $(RM) $(TEST_PROGRAMS) $(RM) -r bin-wrappers + $(RM) -r $(dep_dirs) $(RM) *.spec *.pyc *.pyo */*.pyc */*.pyo common-cmds.h TAGS tags cscope* $(RM) -r autom4te.cache $(RM) config.log config.mak.autogen config.mak.append config.status config.cache
-- 1.6.6