Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!oliveb!felix!dhw68k!arcturus!evil
From: evil@arcturus.UUCP (Wade Guthrie)
Newsgroups: comp.lang.c
Subject: Re: C optimizer
Summary: what kind of optimizers
Keywords: C Ultrix
Message-ID: <3684@arcturus>
Date: 14 Feb 89 21:15:49 GMT
References: <515@larry.UUCP>
Organization: Rockwell International, Anaheim, CA
Lines: 27

In article <515@larry.UUCP>, jwp@larry.UUCP (Jeffrey W Percival) writes:
 
> my real question is, would *most* compilers optimize this . . .

While we're talking about optimizers (and, since all the furor about
optimizing one's code has died down :->), what do most optimizers on
most C compilers do?  Where is TFM that I should be 'R'ing (and in which
FM should I look?)  I would expect the following optimizations:

	1) constant expression reduction
	2) loop inversion
	3) reducing things like intval/2 == intval >> 1 when they are
	   faster.  I actually saw a programmer write something
	   LAST YEAR that used intval >> n instead of dividing.  Scary.

What else should I expect?  From what compilers?  On what machines?
In short, what should I do myself and what should I let the *general*
optimizer/compiler do?


Wade Guthrie
evil@arcturus.UUCP
Rockwell International
Anaheim, CA

(Rockwell doesn't necessarily believe / stand by what I'm saying; how could
they when *I* don't even know what I'm talking about???)