Override built-in rules of GNU make that use a wildcard target. This
speeds things up significantly as we don't need to stat() so many
files just in case we'd be able to retrieve their contents from RCS or
SCCS. See [1] for an old mailing list discussion about how to disable
these.
This gives us a noticeable speedup on a no-op run:
$ git hyperfine -L rev HEAD~1,HEAD~0 -s 'make -j8 all NO_TCLTK=Y' 'make NO_TCLTK=Y' --warmup 10 -M 10
Benchmark 1: make NO_TCLTK=Y' in 'HEAD~1
Time (mean ± σ): 182.2 ms ± 4.1 ms [User: 146.8 ms, System: 49.5 ms]
Range (min … max): 179.6 ms … 193.4 ms 10 runs
Benchmark 2: make NO_TCLTK=Y' in 'HEAD~0
Time (mean ± σ): 167.9 ms ± 1.3 ms [User: 127.8 ms, System: 55.6 ms]
Range (min … max): 166.1 ms … 170.4 ms 10 runs
Summary
'make NO_TCLTK=Y' in 'HEAD~0' ran
1.09 ± 0.03 times faster than 'make NO_TCLTK=Y' in 'HEAD~1'
Running the same except with 'strace -c -S calls make' as the
benchmark command shows (under --show-output) that we went from ~7716
syscalls to ~7519, mostly a reduction in [l]stat().
1. https://lists.gnu.org/archive/html/help-make/2002-11/msg00063.html
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@xxxxxxxxx>
---
shared.mak | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/shared.mak b/shared.mak
index 4ee0bb7a13d..4862df1607a 100644
--- a/shared.mak
+++ b/shared.mak
@@ -1,3 +1,14 @@
+### Remove GNU make implicit rules
+
+## This speeds things up since we don't need to look for and stat() a
+## "foo.c,v" every time a rule referring to "foo.c" is in play. See
+## "make -p -f/dev/null | grep ^%::'".
+%:: %,v
+%:: RCS/%,v
+%:: RCS/%
+%:: s.%
+%:: SCCS/s.%
+
### Flags affecting all rules
# A GNU make extension since gmake 3.72 (released in late 1994) to
--
2.34.0.795.g1e9501ab396
