Precompile headers

This cuts 'make install -j6' on my laptop from 170s to 134s.

1 files changed, 42 insertions, 0 deletions

diff --git a/mk/precompiled-headers.mk b/mk/precompiled-headers.mk
new file mode 100644
index 000000000..779389b26
--- /dev/null
+++ b/mk/precompiled-headers.mk
@@ -0,0 +1,42 @@
+PRECOMPILE_HEADERS ?= 1
+
+print-var-help += \
+  echo "  PRECOMPILE_HEADERS ($(PRECOMPILE_HEADERS)): Whether to use precompiled headers to speed up the build";
+
+GCH = $(buildprefix)precompiled-headers.h.gch
+
+$(GCH): precompiled-headers.h
+	@rm -f $@
+	@mkdir -p "$(dir $@)"
+	$(trace-gen) $(CXX) -x c++-header -o $@ $^ $(GLOBAL_CXXFLAGS)
+
+PCH = $(buildprefix)precompiled-headers.h.pch
+
+$(PCH): precompiled-headers.h
+	@rm -f $@
+	@mkdir -p "$(dir $@)"
+	$(trace-gen) $(CXX) -x c++-header -o $@ $^ $(GLOBAL_CXXFLAGS)
+
+clean-files += $(GCH) $(PCH)
+
+ifeq ($(PRECOMPILE_HEADERS), 1)
+
+  ifeq ($(CXX), g++)
+
+    GLOBAL_CXXFLAGS_PCH += -include $(buildprefix)precompiled-headers.h -Winvalid-pch
+
+    GLOBAL_ORDER_AFTER += $(GCH)
+
+  else ifeq ($(CXX), clang++)
+
+    GLOBAL_CXXFLAGS_PCH += -include-pch $(PCH) -Winvalid-pch
+
+    GLOBAL_ORDER_AFTER += $(PCH)
+
+  else
+
+    $(error Don't know how to precompile headers on $(CXX))
+
+  endif
+
+endif