2021-01-01 16:03:39 +08:00
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# Copyright (C) 2016-2021 Free Software Foundation, Inc.
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Makefiles: Disable suffix rules and implicit rules
Since we don't use suffix rules nor implicit rules in gdb, we can
disable them. The advantage is a slightly faster make [1].
Here are some numbers about the speedup. I ran this on my trusty old
Intel Q6600, so the time numbers are probably higher than what you'd get
on any recent hardware. I ran "make" in the gdb/ directory of an
already built repository (configured with --enable-targets=all). I
recorded the time of execution (average of 5). I then ran "make -d" and
recorded the number of printed lines, which gives a rough idea of the
number of operations done.
I compared the following configurations, to see the impact of both the
empty .SUFFIXES target and the empty pattern rules, as well as running
"make -r", which can be considered the "ideal" case.
A - baseline
B - baseline + .SUFFIXES
C - baseline + pattern rules
D - baseline + .SUFFIXES + pattern rules
E - baseline + make -r
config | time (s) | "make -d"
-----------------------------
A | 5.74 | 2396643
B | 1.19 | 298469
C | 2.81 | 1266573
D | 1.13 | 245489
E | 1.01 | 163914
We can see that the empty .SUFFIXES target has a bigger impact than the
empty pattern rules, but still it doesn't hurt to disable the implicit
pattern rules as well.
There are still some mentions of implicit rules I can't get rid of in
the "make -d" output. For example, it's trying to build .c files from
.w files:
Looking for an implicit rule for '/home/simark/src/binutils-gdb/gdb/infrun.c'.
Trying pattern rule with stem 'infrun'.
Trying implicit prerequisite '/home/simark/src/binutils-gdb/gdb/infrun.w'.
and trying to build Makefile.in from a bunch of extensions:
Looking for an implicit rule for 'Makefile.in'.
Trying pattern rule with stem 'Makefile.in'.
Trying implicit prerequisite 'Makefile.in.o'.
Trying pattern rule with stem 'Makefile.in'.
Trying implicit prerequisite 'Makefile.in.c'.
Trying pattern rule with stem 'Makefile.in'.
Trying implicit prerequisite 'Makefile.in.cc'.
... many more ...
If somebody knows how to disable them, we can do it, but at this point
the returns are minimal, so it is not that important.
I verified that both in-tree and out-of-tree builds work.
[1] Switching from explicit rules to pattern rules for files in
subdirectories actually made it slower, so this is kind of a way to
redeem myself. But it the end it's faster than it was previously,
so it was all worth it. :)
gdb/ChangeLog:
* disable-implicit-rules.mk: New file.
* Makefile.in: Include disable-implicit-rules.mk.
* data-directory/Makefile.in: Likewise.
* gnulib/Makefile.in: Likewise.
gdb/doc/ChangeLog:
* Makefile.in: Likewise.
gdb/gdbserver/ChangeLog:
* Makefile.in: Include disable-implicit-rules.mk.
gdb/testsuite/ChangeLog:
* Makefile.in: Include disable-implicit-rules.mk.
2016-12-01 05:23:59 +08:00
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# This file is part of GDB.
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 3 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program. If not, see <http://www.gnu.org/licenses/>.
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# An empty .SUFFIXES target clears the suffixes list, which will skip lookups
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# of many implicit rules, speeding up the execution of make.
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.SUFFIXES:
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# Disable some implicit pattern rules.
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%: %,v
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%: RCS/%,v
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%: RCS/%
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%: s.%
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%: SCCS/s.%
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