libgo patch committed: Only rebuild package if dependent .gox changed

libgo patch committed: Only rebuild package if dependent .gox changed

[Ian Lance Taylor]

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This patch to libgo tweaks the libgo Makefile so that we only rebuild
a package if the .gox file of some imported package changes.  We now
use mvifdiff and stamp files to track whether a .gox file has changed.
When package A depends on package B, and we rebuild package B, we only
rebuild package A if package B's .gox file changes.  This is safe
because when package A imports package B it only reads package B's
.gox file.  This means that changes that do not affect export
information will not cause dependent packages to be recompiled.  This
doesn't matter in a clean build, but it speeds up an incremental build
when the export information does not change.  Bootstrapped and ran Go
testsuite on x86_64-pc-linux-gnu.  Committed to mainline.

Ian

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Index: gcc/go/gofrontend/MERGE
===================================================================
--- gcc/go/gofrontend/MERGE	(revision 241741)
+++ gcc/go/gofrontend/MERGE	(working copy)
@@ -1,4 +1,4 @@
-9ee8ad540d6f2f77af1821bfd977dc1820e1be8f
+90f12ac1fa72a95e73cb88b6114fa3131c4ca8ee
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.
Index: libgo/Makefile.am
===================================================================
--- libgo/Makefile.am	(revision 241741)
+++ libgo/Makefile.am	(working copy)
@@ -924,7 +924,8 @@ BUILDPACKAGE = \
 # How to build a .gox file from a .lo file.
 BUILDGOX = \
 	f=`echo $< | sed -e 's/.lo$$/.o/'`; \
-	$(OBJCOPY) -j .go_export $$f $@.tmp && mv -f $@.tmp $@
+	$(OBJCOPY) -j .go_export $$f $@.tmp; \
+	$(SHELL) $(srcdir)/mvifdiff.sh $@.tmp `echo $@ | sed -e 's/s-gox/gox/'`
 
 GOTESTFLAGS =
 GOBENCH = 
@@ -1022,8 +1023,10 @@ $(1).lo:
 $(1)/check: $$(CHECK_DEPS)
 	@$$(CHECK)
 .PHONY: $(1)/check
-$(1).gox: $(1).lo
+$(1).gox: $(1).s-gox; @true
+$(1).s-gox: $(1).lo
 	$$(BUILDGOX)
+	$$(STAMP) $$@
 endef
 
 # This line expands PACKAGE_template once for each package name listed