From:	quacci AT vera DOT com (jon)
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: Any tips on optimizing C code?
Date:	Fri, 23 May 1997 03:36:39 GMT
Organization:	Yale University
Message-ID:	<33850f40.4566839@news.cis.yale.edu>
References:	<33775c59 DOT 19219875 AT news DOT cis DOT yale DOT edu> <5l8nqq$f5e AT freenet-news DOT carleton DOT ca>
NNTP-Posting-Host:	slip-ppp-node-12.cs.yale.edu
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To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

On 13 May 1997 03:40:10 GMT, ao950 AT FreeNet DOT Carleton DOT CA (Paul
Derbyshire) wrote:

<...>

>Compile with -m486, since anything speed-requiring should be run on 486
>and up nowadays. This causes gcc to optimize for 486 and up chips.

Two things about this- firstly, since i am linking separately from my
compile line, should I also link with a -m486? I've tried, and I get
no complaints... but I also don't know what I'm asking the linker to
do!

Secondly, what are all the "alignment problems" I keep seeing flash by
this newsgroup regarding something to do with -m486? I have notice a
speed increase compiling with it, so this isn't really a key issue; it
works in what I'm doing now nicely.

<...>

>A function
>called frequently, especially recursively or in inner loops, can be
>declared "register"

I'd never thought of that- thanks!

> and registers are used to pass parameters instead of
>the stack. If the function has only two or three arguments, they all get
>passed by register. This saves a lot of push and pop instructions, but it
>might cause gcc to juggle registers instead, so test your program's speed
>with and without this for each function. It of course does not affect
>functions with no arguments.

Great stuff. Thanks.

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