Date: Wed, 13 Sep 2006 11:08:48 -0600 (MDT) From: "M. Warner Losh" <imp@bsdimp.com> To: freebsd-arm@FreeBSD.org Subject: Re: -O2 optimization Message-ID: <20060913.110848.-311941144.imp@bsdimp.com> In-Reply-To: <20060911163218.GA88778@dragon.NUXI.org> References: <20060911163218.GA88778@dragon.NUXI.org>
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In message: <20060911163218.GA88778@dragon.NUXI.org>
"David O'Brien" <obrien@FreeBSD.org> writes:
: I've been wondering. Since most ARM platforms are RAM and storage
: limited, should we not compile with -O2 and use -Os instead.
:
: -Os is "Optimize for size. -Os enables all -O2 optimizations that do not
: typically increase code size. It also performs further optimizations
: designed to reduce code size".
:
: So what do folks think about this patch?
I like the idea, but I'm not sure I like the testing of MACHINE_ARCH
directly for this. Maybe something like OPT_SMALL being defined
instead? However, the following change saved ~65kB in a ~1900kB
kernel I just built, or about 3%. That seems signficant enough to me
to have a knob for.
: Index: kern.pre.mk
: ===================================================================
: RCS file: /home/ncvs/src/sys/conf/kern.pre.mk,v
: retrieving revision 1.76
: diff -u -p -r1.76 kern.pre.mk
: --- kern.pre.mk 17 Jul 2006 18:43:16 -0000 1.76
: +++ kern.pre.mk 11 Sep 2006 16:29:47 -0000
: @@ -27,7 +27,11 @@ COPTFLAGS?= -O
: . if defined(DEBUG)
: _MINUS_O= -O
: . else
: +. if ${MACHINE_ARCH} == "arm"
: +_MINUS_O= -Os
: +. else
: _MINUS_O= -O2
: +. endif
: . endif
: . if ${MACHINE_ARCH} == "amd64"
: COPTFLAGS?=-O2 -frename-registers -pipe
:
: --
: -- David (obrien@FreeBSD.org)
: Q: Because it reverses the logical flow of conversation.
: A: Why is top-posting (putting a reply at the top of the message) frowned upon?
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