Path: utzoo!attcan!uunet!lll-winken!lll-tis!mordor!joyce!sri-unix!garth!smryan
From: smryan@garth.UUCP (Steven Ryan)
Newsgroups: comp.lang.misc
Subject: Re: Query re optimising compilers
Message-ID: <1143@garth.UUCP>
Date: 2 Aug 88 19:21:36 GMT
References: <561@etive.ed.ac.uk> <5423@ihlpf.ATT.COM> <6376@aw.sei.cmu.edu> <8445@ihlpb.ATT.COM>
Reply-To: smryan@garth.UUCP (Steven Ryan)
Organization: INTERGRAPH (APD) -- Palo Alto, CA
Lines: 12

>                               However, this brings up another question:
>is this truly an optimization?  The way I (used to?) think about
>optimization with respect to execution speed is that
>
>	speed of optimized code >= speed of unoptimized code
>
>for *all instantiations* of a given source statement.

The fine print has always read that it is attempt to speedup a program that
helps in most cases, but once in while hurts.

The various optimisations interact in a nonlinear way so that any attempt
to get better code will sometimes produce worse code.