Xref:	news2.mv.net comp.os.msdos.djgpp:3635
From:	malcolm AT manawatu DOT gen DOT nz (Malcolm Taylor)
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: mov %eax, %eax in generated asm source
Date:	Thu, 09 May 1996 10:19:41 GMT
Organization:	Grafik Software
Lines:	28
Message-ID:	<4mskgp$ce4@news.manawatu.gen.nz>
References:	<4mnhbv$qs2 AT doc DOT zippo DOT com>
Reply-To:	malcolm AT manawatu DOT gen DOT nz
NNTP-Posting-Host:	malcolm.manawatu.gen.nz
Mime-Version:	1.0
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

Mark Wayland wrote:

>Hi all,

>Can I ask what may potentially be a stupid question ? Well, I will anyway ...

>Can anyone tell me the purpose of the code that is generated by

>gcc -S fred.c

>whereby it generates

>mov %eax, %eax

>???? It seems like a time-waster to me ??

It is :). GCC will often create seemingly stupid arrangements of
asembler instructions when not optimising as it doesn't take much
account of previous instructions it has output. This probably came
about from the need to shift a variable into eax, which just happened
to be in eax.
The solution is to compile with optimizations (eg -O2) and you'll
these will disappear.

Malcolm

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