From f94a3edc6e4245f10e245d162737b889788f4f12 Mon Sep 17 00:00:00 2001
From: Ian Lance Taylor <ian@gcc.gnu.org>
Date: Tue, 1 Nov 2016 13:54:21 +0000
Subject: [PATCH] libgo: only rebuild package if dependent .gox has changed

    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, 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.

    Reviewed-on: https://go-review.googlesource.com/32476

From-SVN: r241742
---
 gcc/go/gofrontend/MERGE | 2 +-
 libgo/Makefile.am       | 7 +++++--
 libgo/Makefile.in       | 7 +++++--
 3 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/gcc/go/gofrontend/MERGE b/gcc/go/gofrontend/MERGE
index d5240a91941..4dd1f8c4ead 100644
--- a/gcc/go/gofrontend/MERGE
+++ b/gcc/go/gofrontend/MERGE
@@ -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.
diff --git a/libgo/Makefile.am b/libgo/Makefile.am
index 0356de8a71f..edf193a5d40 100644
--- a/libgo/Makefile.am
+++ b/libgo/Makefile.am
@@ -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
diff --git a/libgo/Makefile.in b/libgo/Makefile.in
index 140cfdf2aeb..908e66042a5 100644
--- a/libgo/Makefile.in
+++ b/libgo/Makefile.in
@@ -1079,7 +1079,8 @@ 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 = 
@@ -3366,8 +3367,10 @@ $(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
-- 
2.30.2