1 files changed, 13 insertions, 2 deletions

diff --git a/Makefile.in b/Makefile.in
index ae92424bf8e..abd61490fbe 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -315,10 +315,21 @@ lib-src: FRC src/config.stamp
 # We need to build `emacs' in `src' to compile the *.elc files in `lisp'.
 lisp: src
 
+# Pass to src/Makefile.in an additional BOOTSTRAPEMACS variable which
+# is either set to bootstrap-emacs (in case bootstrap-emacs has not been
+# constructed yet) or the empty string (otherwise).
+# src/Makefile.in uses it to implement conditional dependencies, so that
+# files that need bootstrap-emacs to be built do not additionally need
+# to be kept fresher than bootstrap-emacs.  Otherwise changing a single
+# file src/foo.c forces dumping a new bootstrap-emacs, then re-byte-compiling
+# all preloaded elisp files, and only then dump the actual src/emacs, which
+# is not wrong, but is overkill in 99.99% of the cases.
 ${SUBDIR}: ${SUBDIR_MAKEFILES} FRC
-        cd $@; $(MAKE) all $(MFLAGS) \
+        boot=bootstrap-emacs$(EXEEXT);                         \
+        if [ -x "src/$$boot" ]; then boot=""; fi;                   \
+        cd $@; $(MAKE) all $(MFLAGS)                           \
           CC='${CC}' CFLAGS='${CFLAGS}' CPPFLAGS='${CPPFLAGS}' \
-          LDFLAGS='${LDFLAGS}' MAKE='${MAKE}'
+          LDFLAGS='${LDFLAGS}' MAKE='${MAKE}' BOOTSTRAPEMACS="$$boot"
 
 blessmail: ${SUBDIR_MAKEFILES} src FRC
         cd lib-src; $(MAKE) maybe-blessmail $(MFLAGS) \