Bootstrap optimization

[Mikael Djurfeldt <mikael@djurfeldt.com>]

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I find that the attached patch saves a few minutes for parallel builds on a
four core machine. What it does is to build both eval.go and psyntax.pp.go
serially before the rest is built in parallel (when make is given -j).

Here's an attempt at explanation why this saves time:

Let's denote the .go objects by numbers 1, 2, ... where 1 is eval.go and 2
is psyntax.pp.go. We also prepend a prefix "S" for a slow build with
interpreted psyntax.pp and "F" for a fast build.

Assuming a four core machine, we previously had something like:

S1
S2 S3 S4 S5
     S6 S7 S8 (since S2 builds so slowly)
F9 F10 ...

Now, instead, we have:

S1
S2
F3 F4 F5 F6
...

On my machine, the patch saved 10 minutes out of 55 minutes without the
patch.

To which branch should this be applied, stable-2.2 or master?

Best regards,
Mikael

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From 0fe521100487411a2c48f6af14796a22964844a1 Mon Sep 17 00:00:00 2001
From: Mikael Djurfeldt <mikael@djurfeldt.com>
Date: Thu, 25 Oct 2018 13:53:47 +0200
Subject: [PATCH] Bootstrap optimization

* bootstrap/Makefile.am: Build both eval.go and psyntax-pp.go before the rest
  of the .go files so that they are handled by a fast macro expander. This
  saves time for a parallel build.
---
 bootstrap/Makefile.am | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/bootstrap/Makefile.am b/bootstrap/Makefile.am
index 57b62eb56..3e92ef1af 100644
--- a/bootstrap/Makefile.am
+++ b/bootstrap/Makefile.am
@@ -32,5 +32,8 @@ GUILE_OPTIMIZATIONS = -O1 -Oresolve-primitives
 include $(top_srcdir)/am/bootstrap.am
 
 # We must build the evaluator first, so that we can be sure to control
-# the stack.
-$(filter-out ice-9/eval.go, $(GOBJECTS)): ice-9/eval.go
+# the stack. Then, we build the syntax-case macro expander before the
+# rest, in order to speed up parallel builds.
+ice-9/psyntax-pp.go: ice-9/eval.go
+
+$(filter-out ice-9/eval.go ice-9/psyntax-pp.go, $(GOBJECTS)): ice-9/psyntax-pp.go
-- 
2.11.0