Re: Speeding up the bootstrap build - a quick hack.

[Alan Mackenzie <acm@muc.de>]

Hello, Robert.

On Thu, Jan 20, 2022 at 10:25:26 +0100, Robert Pluim wrote:
> >>>>> On Wed, 19 Jan 2022 21:32:30 +0000, Alan Mackenzie <acm@muc.de> said:

>     Alan> This was surprisingly difficult to solve.  There appears to be no way in
>     Alan> make to set a variable depending on what the target is.  The make manual
>     Alan> doesn't say this explicitly, it just depends on vagueness.  After an hour
>     Alan> of searching for such a feature, it gradually dawns on you that there is
>     Alan> no such feature, even though one might be expected.  I'm glad the Emacs
>     Alan> manuals aren't like that.

> "Target-specific Variable Values" in the Gnu Make info manual. eg

> Makefile:

> FOO=bar

> default:
> 	@echo FOO=$(FOO)

> foo: FOO=foo
> foo:
> 	@echo FOO=$(FOO)

> results:

> > make
> FOO=bar
> > make foo
> FOO=foo

Thank you indeed.  That's exactly what I needed.  I've amended my patch to use
this.

So, if there are no objections, I'll be committing the following to
master within the next day or so:


In early bootstrap, use byte-compiled compiler to native compile first files

This speeds up a make bootstrap by around 15%.

* lisp/Makefile.in (BYTE_COMPILE_FLAGS): set a value specific to compile-first
which doesn't contain the setting of Emacs variable load-prefer-newer.
Add a new make hunk which byte-compiles (rather then native compiles) when the
environment variable ANCIENT is "yes".  Set the date of the .elc files built
to 1970-01-01 to cause a second compilation of them later.

* src/Makefile.in: Add an extra invocation of directory lisp's MAKE with
target compile-first and the flag environment variable ANCIENT set to yes.

* src/verbose.mk.in: When ANCIENT is yes, output ELC, not ELC+ELN for
AM_V_ELC.



diff --git a/lisp/Makefile.in b/lisp/Makefile.in
index 3a72034463..3d03b16331 100644
--- a/lisp/Makefile.in
+++ b/lisp/Makefile.in
@@ -77,6 +77,8 @@ AUTOGENEL =
 # Set load-prefer-newer for the benefit of the non-bootstrappers.
 BYTE_COMPILE_FLAGS = \
   --eval '(setq load-prefer-newer t)' $(BYTE_COMPILE_EXTRA_FLAGS)
+# ... but we must prefer .elc files for those in the early bootstrap.
+compile-first: BYTE_COMPILE_FLAGS = $(BYTE_COMPILE_EXTRA_FLAGS)
 
 # Files to compile before others during a bootstrap.  This is done to
 # speed up the bootstrap process.  They're ordered by size, so we use
@@ -303,9 +305,22 @@ .SUFFIXES:
 # An old-fashioned suffix rule, which, according to the GNU Make manual,
 # cannot have prerequisites.
 ifeq ($(HAVE_NATIVE_COMP),yes)
+ifeq ($(ANCIENT),yes)
+# The first compilation of compile-first, using an interpreted compiler:
+# The resulting .elc files get given a date of 1970-01-01 so that their
+# date stamp is earlier than the source files, causing these to be compiled
+# into native code at the second recursive invocation of this $(MAKE),
+# using these .elc's.  This is faster than just compiling the native code
+# directly using the interpreted compile-first files.
+.el.elc:
+	$(AM_V_ELC)$(emacs) $(BYTE_COMPILE_FLAGS) \
+	-l comp -f batch-byte-compile $<
+	touch -t 197001010000 $@
+else
 .el.elc:
 	$(AM_V_ELC)$(emacs) $(BYTE_COMPILE_FLAGS) \
 	-l comp -f batch-byte+native-compile $<
+endif
 else
 .el.elc:
 	$(AM_V_ELC)$(emacs) $(BYTE_COMPILE_FLAGS) -f batch-byte-compile $<
diff --git a/src/Makefile.in b/src/Makefile.in
index 04fabd5f42..13392bfad6 100644
--- a/src/Makefile.in
+++ b/src/Makefile.in
@@ -914,6 +914,9 @@ $(bootstrap_pdmp):
 	$(RUN_TEMACS) --batch $(BUILD_DETAILS) -l loadup --temacs=pbootstrap \
 		--bin-dest $(BIN_DESTDIR) --eln-dest $(ELN_DESTDIR)
 	@: Compile some files earlier to speed up further compilation.
+	@: First, byte compile these files, ....
+	ANCIENT=yes $(MAKE) -C ../lisp compile-first EMACS="$(bootstrap_exe)"
+	@: .... then use their .elcs in native compiling these and other files.
 	$(MAKE) -C ../lisp compile-first EMACS="$(bootstrap_exe)"
 endif
 
diff --git a/src/verbose.mk.in b/src/verbose.mk.in
index e3f5678303..01076df946 100644
--- a/src/verbose.mk.in
+++ b/src/verbose.mk.in
@@ -40,12 +40,17 @@ AM_V_CXX     = @$(info $   CXX      $@)
 AM_V_CCLD    = @$(info $   CCLD     $@)
 AM_V_CXXLD   = @$(info $   CXXLD    $@)
 ifeq ($(HAVE_NATIVE_COMP),yes)
-ifeq ($(NATIVE_DISABLED),1)
+ifneq ($(NATIVE_DISABLED),1)
+ifneq ($(ANCIENT),yes)
+AM_V_ELC     = @$(info $   ELC+ELN  $@)
+AM_V_ELN     = @$(info $   ELN      $@)
+else
 AM_V_ELC     = @$(info $   ELC      $@)
 AM_V_ELN =
+endif
 else
-AM_V_ELC     = @$(info $   ELC+ELN  $@)
-AM_V_ELN     = @$(info $   ELN      $@)
+AM_V_ELC     = @$(info $   ELC      $@)
+AM_V_ELN =
 endif
 else
 AM_V_ELC     = @$(info $   ELC      $@)


> Robert
> -- 

-- 
Alan Mackenzie (Nuremberg, Germany).