https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118223
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
here is an example of how GCC handles an auto-generated file which is
definitely not stored in SCM:
```
TARGET_H = $(TM_H) target.h $(TARGET_DEF) insn-modes.h insn-codes.h
FLAGS_H = flags.h flag-types.h $(OPTIONS_H)
OPTIONS_H = options.h flag-types.h $(OPTIONS_H_EXTRA)
TM_H = $(GTM_H) insn-flags.h $(OPTIONS_H)
RTL_H = $(RTL_BASE_H) $(FLAGS_H) genrtl.h
...
# For each of the files generated by running a generator program over
# the machine description, the following static pattern rules run the
# generator program only if the machine description has changed,
# but touch the target file only when its contents actually change.
# The "; @true" construct forces Make to recheck the timestamp on
# the target file.
simple_rtl_generated_h = insn-attr.h insn-attr-common.h insn-codes.h \
insn-config.h insn-flags.h insn-target-def.h
simple_rtl_generated_c = insn-automata.cc \
insn-extract.cc insn-output.cc \
insn-peep.cc
simple_generated_h = $(simple_rtl_generated_h) insn-constants.h
simple_generated_c = $(simple_rtl_generated_c) insn-enums.cc
$(simple_generated_h:insn-%.h=s-%) \
$(simple_generated_c:insn-%.cc=s-%): s-%: $(MD_DEPS)
$(simple_rtl_generated_h:insn-%.h=s-%) \
$(simple_rtl_generated_c:insn-%.cc=s-%): s-%: insn-conditions.md
$(simple_generated_h): insn-%.h: s-%; @true
$(simple_generated_h:insn-%.h=s-%): s-%: build/gen%$(build_exeext)
$(RUN_GEN) build/gen$*$(build_exeext) $(md_file) \
$(filter insn-conditions.md,$^) > tmp-$*.h
$(SHELL) $(srcdir)/../move-if-change tmp-$*.h insn-$*.h
$(STAMP) s-$*
$(simple_generated_c): insn-%.cc: s-%; @true
$(simple_generated_c:insn-%.cc=s-%): s-%: build/gen%$(build_exeext)
$(RUN_GEN) build/gen$*$(build_exeext) $(md_file) \
$(filter insn-conditions.md,$^) > tmp-$*.cc
$(SHELL) $(srcdir)/../move-if-change tmp-$*.cc insn-$*.cc
$(STAMP) s-$*
...
generated_files = config.h tm.h $(TM_P_H) $(TM_D_H) $(TM_H) multilib.h \
$(simple_generated_h) specs.h \
tree-check.h genrtl.h insn-modes.h insn-modes-inline.h \
tm-preds.h tm-constrs.h \
$(ALL_GTFILES_H) gtype-desc.cc gtype-desc.h version.h \
options.h target-hooks-def.h insn-opinit.h \
common/common-target-hooks-def.h pass-instances.def \
$(GIMPLE_MATCH_PD_SEQ_SRC) $(GENERIC_MATCH_PD_SEQ_SRC) \
gimple-match-auto.h generic-match-auto.h \
c-family/c-target-hooks-def.h d/d-target-hooks-def.h \
$(TM_RUST_H) rust/rust-target-hooks-def.h \
case-cfn-macros.h \
cfn-operators.pd omp-device-properties.h
options.h: s-options-h ; @true
s-options-h: optionlist $(srcdir)/opt-functions.awk $(srcdir)/opt-read.awk \
$(srcdir)/opth-gen.awk
$(AWK) -f $(srcdir)/opt-functions.awk -f $(srcdir)/opt-read.awk \
-f $(srcdir)/opth-gen.awk \
< $< > tmp-options.h
$(SHELL) $(srcdir)/../move-if-change tmp-options.h options.h
$(STAMP) $@
...
# In order for parallel make to really start compiling the expensive
# objects from $(OBJS) as early as possible, build all their
# prerequisites strictly before all objects.
$(ALL_HOST_OBJS) : | $(generated_files)
# Include the auto-generated dependencies for all host objects.
DEPFILES = \
$(foreach obj,$(ALL_HOST_OBJS),\
$(dir $(obj))$(DEPDIR)/$(patsubst %.o,%.Po,$(notdir $(obj))))
-include $(DEPFILES)
```
And yes this is complex
