From owner-cvs-all  Fri Jan  4 18:36:21 2002
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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
References: <200201042213.g04MDBg93058@aslan.scsiguy.com>
From: Dag-Erling Smorgrav <des@ofug.org>
Date: 05 Jan 2002 02:58:11 +0100
In-Reply-To: <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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