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Makefile.in: Document the use of stamps. 

* Makefile.in: Document the use of stamps.

From-SVN: r108156
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Rafael Ávila de Espíndola 2005-12-07 21:54:48 +10:30 committed by Alan Modra
parent 2f4d2d181a
commit f637f07220
2 changed files with 41 additions and 3 deletions
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4
gcc/ChangeLog
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@ -1,3 +1,7 @@
2005-12-07 Rafael Ávila de Espíndola <rafael.espindola@gmail.com>
* Makefile.in: Document the use of stamps.
2005-12-07 Rafael Ávila de Espíndola <rafael.espindola@gmail.com>
* doc/gty.texi: Remove instructions for adding a dependency on s-gtype.

40
gcc/Makefile.in
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@ -1095,6 +1095,42 @@ endif
# Rebuilding this configuration
# -----------------------------
# On the use of stamps:
# Consider the example of tree-check.h. It is constructed with build/gencheck.
# A simple rule to build tree-check.h would be
# tree-check.h: build/gencheck$(build_exeext)
# $(RUN_GEN) build/gencheck$(build_exeext) > tree-check.h
#
# but tree-check.h doesn't change every time gencheck changes. It would the
# nice if targets that depend on tree-check.h wouldn't be rebuild
# unnecessarily when tree-check.h is unchanged. To make this, tree-check.h
# must not be overwritten with a identical copy. One solution is to use a
# temporary file
# tree-check.h: build/gencheck$(build_exeext)
# $(RUN_GEN) build/gencheck$(build_exeext) > tree-check.h
# $(SHELL) $(srcdir)/../move-if-change tmp-check.h tree-check.h
#
# This solution has a different problem. Since the time stamp of tree-check.h
# is unchanged, make will try to update tree-check.h every time it runs.
# To prevent this, one can add a stamp
# tree-check.h: s-check
# s-check : build/gencheck$(build_exeext)
# $(RUN_GEN) build/gencheck$(build_exeext) > tree-check.h
# $(SHELL) $(srcdir)/../move-if-change tmp-check.h tree-check.h
# $(STAMP) s-check
#
# The problem with this solution is that make thinks that tree-check.h is
# always unchanged. Make must be deceived into thinking that tree-check.h is
# rebuild by the "a: s-a" rule. To do this, add a dummy command:
# tree-check.h: s-check; @true
# s-check : build/gencheck$(build_exeext)
# $(RUN_GEN) build/gencheck$(build_exeext) > tree-check.h
# $(SHELL) $(srcdir)/../move-if-change tmp-check.h tree-check.h
# $(STAMP) s-check
#
# This is what is done in this makefile. Note that mkconfig.sh has a
# move-if-change built-in
Makefile: config.status $(srcdir)/Makefile.in $(LANG_MAKEFRAGS)
LANGUAGES="$(CONFIG_LANGUAGES)" \
CONFIG_HEADERS= \
@ -2700,9 +2736,7 @@ s-output : $(MD_DEPS) build/genoutput$(build_exeext)
genrtl.o : genrtl.c $(CONFIG_H) $(SYSTEM_H) coretypes.h $(TM_H) $(RTL_H) \
$(GGC_H)
genrtl.c genrtl.h : s-genrtl
@true # force gnu make to recheck modification times.
genrtl.c genrtl.h : s-genrtl; @true
s-genrtl: build/gengenrtl$(build_exeext)
$(RUN_GEN) build/gengenrtl$(build_exeext) -h > tmp-genrtl.h
$(SHELL) $(srcdir)/../move-if-change tmp-genrtl.h genrtl.h