Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!mcsun!ukc!dcl-cs!aber-cs!athene!pcg From: pcg@cs.aber.ac.uk (Piercarlo Grandi) Newsgroups: comp.lang.misc Subject: Re: Aggressive optimization Message-ID: Date: 4 Nov 90 21:16:13 GMT References: <4699@lanl.gov> <2028@exodus.Eng.Sun.COM> Sender: pcg@aber-cs.UUCP Organization: Coleg Prifysgol Cymru Lines: 33 In-reply-to: grover@brahmand.Eng.Sun.COM's message of 3 Nov 90 04:16:26 GMT On 3 Nov 90 04:16:26 GMT, grover@brahmand.Eng.Sun.COM (Vinod Grover) said: grover> In article grover> pcg@cs.aber.ac.uk (Piercarlo Grandi) writes: pcg> The burden of proof is on proponents of aggressive optimization, pcg> becasue they have to overcome the obvious observation that anything pcg> that enlarges or complicates a program will tend to decrease its pcg> reliability. grover> I fail to see how an optimiser can complicate a program if it grover> performs its transfromation at an intermediate level. The source grover> program written by the programmer is *not modified* in any way. Sorry if It was not clear from what I wrote that the program I was referring to was the *compiler*. grover> The translation to a complex intermediate form, if correct, does grover> not affect the reliability of the source program. I intended to say that the code that effects the transformation adds to the size and complexity of the compiler and therefore affects the compiler's reliability. Each individual transformation may look simple and safe, but once you consider that you need code also to do the analysis that makes possible and drives the transformation process and you also need to consider he interactions between tranformations, which are difficult to model in languages that have not been designed with transsformations in mind... You have a large amount of hairy code in the compiler's bowels, and this is baaaad. -- Piercarlo "Peter" Grandi | ARPA: pcg%uk.ac.aber.cs@nsfnet-relay.ac.uk Dept of CS, UCW Aberystwyth | UUCP: ...!mcsun!ukc!aber-cs!pcg Penglais, Aberystwyth SY23 3BZ, UK | INET: pcg@cs.aber.ac.uk