Speed up QSTR creation by pre-filtering files before pre-processing.

ports/atmel-samd/Makefile

@@ -427,6 +427,7 @@ endif
 OBJ += $(addprefix $(BUILD)/, $(SRC_S:.s=.o))
 
 SRC_QSTR += $(SRC_C) $(SRC_SUPERVISOR) $(SRC_COMMON_HAL_EXPANDED) $(SRC_SHARED_MODULE_EXPANDED) $(STM_SRC_C)
+SRC_QSTR_PP += peripherals/samd/$(CHIP_FAMILY)/clocks.c
 
 all: $(BUILD)/firmware.bin $(BUILD)/firmware.uf2
 

py/mkrules.mk

@@ -77,9 +77,9 @@ $(OBJ): | $(HEADER_BUILD)/qstrdefs.generated.h $(HEADER_BUILD)/mpversion.h
 # - if anything in QSTR_GLOBAL_DEPENDENCIES is newer, then process all source files ($^)
 # - else, if list of newer prerequisites ($?) is not empty, then process just these ($?)
 # - else, process all source files ($^) [this covers "make -B" which can set $? to empty]
-$(HEADER_BUILD)/qstr.i.last: $(SRC_QSTR) $(QSTR_GLOBAL_DEPENDENCIES) | $(HEADER_BUILD)/mpversion.h
+$(HEADER_BUILD)/qstr.i.last: $(SRC_QSTR) $(SRC_QSTR_PP) $(QSTR_GLOBAL_DEPENDENCIES) | $(HEADER_BUILD)/mpversion.h
 	$(ECHO) "GEN $@"
-	$(Q)$(CPP) $(QSTR_GEN_EXTRA_CFLAGS) $(CFLAGS) $(if $(filter $?,$(QSTR_GLOBAL_DEPENDENCIES)),$^,$(if $?,$?,$^)) >$(HEADER_BUILD)/qstr.i.last;
+	$(Q)grep -lE "(MP_QSTR|i18n)" $(if $(filter $?,$(QSTR_GLOBAL_DEPENDENCIES)),$^,$(if $?,$?,$^)) | xargs $(CPP) $(QSTR_GEN_EXTRA_CFLAGS) $(CFLAGS) $(SRC_QSTR_PP) >$(HEADER_BUILD)/qstr.i.last;
 
 $(HEADER_BUILD)/qstr.split: $(HEADER_BUILD)/qstr.i.last
 	$(STEPECHO) "GEN $@"
@@ -210,4 +210,3 @@ tags:
 	ctags -e -R $(TOP)
 
 -include $(OBJ:.o=.P)
-

py/py.mk

@@ -279,6 +279,8 @@ endif
 # Sources that may contain qstrings
 SRC_QSTR_IGNORE = py/nlr%
 SRC_QSTR = $(SRC_MOD) $(filter-out $(SRC_QSTR_IGNORE),$(PY_CORE_O_BASENAME:.o=.c)) $(PY_EXTMOD_O_BASENAME:.o=.c)
+# Sources that only hold QSTRs after pre-processing.
+SRC_QSTR_PP =
 
 # Anything that depends on FORCE will be considered out-of-date
 FORCE: