Date: 05 Jan 2002 02:58:11 +0100 From: Dag-Erling Smorgrav <des@ofug.org> To: "Justin T. Gibbs" <gibbs@scsiguy.com> Cc: Julian Elischer <julian@elischer.org>, Poul-Henning Kamp <phk@critter.freebsd.dk>, Stephen McKay <mckay@thehub.com.au>, John Baldwin <jhb@FreeBSD.org>, cvs-all@FreeBSD.org, cvs-committers@FreeBSD.org, Julian Elischer <julian@FreeBSD.org>, Greg Lehey <grog@FreeBSD.org> Subject: Re: cvs commit: src/share/man/man3 queue.3 Message-ID: <xzppu4pmudo.fsf@flood.ping.uio.no> In-Reply-To: <200201042213.g04MDBg93058@aslan.scsiguy.com> References: <200201042213.g04MDBg93058@aslan.scsiguy.com>
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"Justin T. Gibbs" <gibbs@scsiguy.com> writes:
> Is the compiler smart enough to not bother testing the result
> of the assignment?
Looks like it:
des@des ~/src% cat >optimize.c
int optimizeme(int i) { for (i = 0; i < 10 || (i = 0); i++) ; return i; }
^D
des@des ~/src% cc -O -o optimize.o -c optimize.c
des@des ~/src% objdump -d optimize.o
optimize.o: file format elf32-i386
Disassembly of section .text:
00000000 <optimizeme>:
0: 55 push %ebp
1: 89 e5 mov %esp,%ebp
3: 31 c0 xor %eax,%eax
5: 8d 76 00 lea 0x0(%esi),%esi
8: 40 inc %eax
9: 83 f8 09 cmp $0x9,%eax
c: 7e fa jle 8 <optimizeme+0x8>
e: 31 c0 xor %eax,%eax
10: c9 leave
11: c3 ret
12: 89 f6 mov %esi,%esi
The result of compiling without -O, btw, is too ugly for words.
DES
--
Dag-Erling Smorgrav - des@ofug.org
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