From cddc27034687e1c3bc52204314dfa46219b5d6f9 Mon Sep 17 00:00:00 2001 From: Austin Clements Date: Wed, 11 Apr 2012 16:38:39 -0400 Subject: [PATCH] Record dependencies during build instead of before Previously, the makefile created dependency files in a separate, first pass. In particular, include-ing the dependency files would cause make to attempt to rebuild those files using the dependency-generation rules in the makefile. Unfortunately, this approach required obtuse rules and silently delayed the start of the build process (by quite a bit on a clean tree without any dependency files). Worse, this required the dependency files to themselves depend on all of the headers the source file depended on, which meant that, if a header file was removed, the depedency file could not be updated because of a missing dependency (!), which would cause make to silently fail. This patch eliminates the dependency generation rules and instead generates dependency files as a side-effect of the regular build rule. On the first build, we don't need to know the dependencies beforehand; the object file doesn't exist, so it will be built anyway. On subsequent builds, if a header file is updated, the dependency rules generated by the previous build will force a rebuild. If a source file is updated, the dependency rules may be stale, but it doesn't matter because the updated source file will force a rebuild. In the final case above, the stale dependency rules may refer to a header file that no longer exists but is also no longer needed. In order to prevent this from breaking the build, we also pass gcc the -MP option, which generates phony targets for every depended-on header file, so make won't complain if it can't find them during a later build. --- Makefile.local | 18 ++++-------------- 1 file changed, 4 insertions(+), 14 deletions(-) diff --git a/Makefile.local b/Makefile.local index 935f0f1e..53b4a0de 100644 --- a/Makefile.local +++ b/Makefile.local @@ -256,22 +256,12 @@ endif quiet ?= $($(shell echo $1 | sed -e s'/ .*//')) %.o: %.cc $(global_deps) - $(call quiet,CXX $(CXXFLAGS)) -c $(FINAL_CXXFLAGS) $< -o $@ + @mkdir -p .deps/$(@D) + $(call quiet,CXX $(CXXFLAGS)) -c $(FINAL_CXXFLAGS) $< -o $@ -MD -MP -MF .deps/$*.d %.o: %.c $(global_deps) - $(call quiet,CC $(CFLAGS)) -c $(FINAL_CFLAGS) $< -o $@ - -.deps/%.d: %.c $(global_deps) - @set -e; rm -f $@; mkdir -p $$(dirname $@) ; \ - $(CC) -M $(CPPFLAGS) $(FINAL_CFLAGS) $< > $@.$$$$ 2>/dev/null ; \ - sed 's,'$$(basename $*)'\.o[ :]*,$*.o $@ : ,g' < $@.$$$$ > $@; \ - rm -f $@.$$$$ - -.deps/%.d: %.cc $(global_deps) - @set -e; rm -f $@; mkdir -p $$(dirname $@) ; \ - $(CXX) -M $(CPPFLAGS) $(FINAL_CXXFLAGS) $< > $@.$$$$ 2>/dev/null ; \ - sed 's,'$$(basename $*)'\.o[ :]*,$*.o $@ : ,g' < $@.$$$$ > $@; \ - rm -f $@.$$$$ + @mkdir -p .deps/$(@D) + $(call quiet,CC $(CFLAGS)) -c $(FINAL_CFLAGS) $< -o $@ -MD -MP -MF .deps/$*.d .PHONY : clean clean: