diff --git a/Makefile.rules b/Makefile.rules
index a6cb6bb30ec..4a2549a592f 100644
--- a/Makefile.rules
+++ b/Makefile.rules
@@ -61,7 +61,7 @@ $(USER_TARGETS)::
 # PRECONDITIONS: that which must be built/checked first
 ################################################################################
 
-SRCMKFILES    := $(filter-out Makefile.rules %.in,\
+SRCMKFILES    := $(BUILD_SRC_DIR)/Makefile $(filter-out Makefile.rules %.in,\
                  $(wildcard $(BUILD_SRC_DIR)/Makefile.*))
 OBJMKFILES    := $(subst $(BUILD_SRC_DIR),$(BUILD_OBJ_DIR),$(SRCMKFILES))
 CONFIGURE     := $(LLVM_SRC_ROOT)/configure
@@ -82,6 +82,8 @@ ifneq ($(strip $(BUILT_SOURCES)),)
 	$(VERB) $(RM) -f $(BUILT_SOURCES)
 endif
 
+$(BUILT_SOURCES) : $(BUILD_OBJ_ROOT)/Makefile
+
 #------------------------------------------------------------------------
 # Make sure we're not using a stale configuration
 #------------------------------------------------------------------------
@@ -806,21 +808,17 @@ YACC_OUTPUT = $(addprefix $(YACC_FILES:%.y=%), .h .cpp .output)
 	$(SED) 's/void yyunput/inline void yyunput/' | \
 	$(SED) 's/void \*yy_flex_realloc/inline void *yy_flex_realloc/' | \
 	$(SED) 's/#define YY_BUF_SIZE 16384/#define YY_BUF_SIZE (16384*64)/' \
-	  > $@.tmp
-	$(VERB) cmp -s $@ $@.tmp > /dev/null || $(MV) -f $@.tmp $@
-	@# remove the output of flex if it didn't get moved over...
-	@rm -f $@.tmp
+	  > $@
 
 # Rule for building the bison parsers...
 %.c: %.y     # Cancel built-in rules for yacc
+%.cpp: %.y   # Cancel built-in rules for yacc
 %.h: %.y     # Cancel built-in rules for yacc
 %.cpp %.h : %.y
 	@$(ECHO) "Bisoning $*.y"
 	$(VERB) $(BISON) -v -d -p $(<F:%Parser.y=%) -o $*.tab.c  $<
-	$(VERB) cmp -s $*.tab.c $*.cpp > /dev/null || $(MV) -f $*.tab.c $*.cpp
-	$(VERB) cmp -s $*.tab.h $*.h   > /dev/null || $(MV) -f $*.tab.h $*.h
-	@# If the files were not updated, don't leave them lying around...
-	@rm -f $*.tab.c $*.tab.h
+	$(VERB) $(MV) -f $*.tab.c $*.cpp
+	$(VERB) $(MV) -f $*.tab.h $*.h
 
 # To create the directories...
 %/.dir: