Path: utzoo!attcan!uunet!husc6!purdue!decwrl!spar!freeman
From: freeman@spar.SPAR.SLB.COM (Jay Freeman)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Knowing Machine Code
Message-ID: <1243@spar.SPAR.SLB.COM>
Date: 14 Jun 88 21:07:36 GMT
References: <13735@comp.vuw.ac.nz> <104700032@uiucdcsp> <4760@husc6.harvard.edu>
Reply-To: freeman@spar.UUCP (Jay Freeman)
Organization: SPAR - Schlumberger Palo Alto Research
Lines: 24

In article <4760@husc6.harvard.edu> singer@endor.UUCP (Rich Siegel) writes:
>In article <104700032@uiucdcsp> gillies@uiucdcsp.cs.uiuc.edu writes:
>
>	Call me stupid, but I fail to see why you need two compilers. Why
>not just have an extremely fast compiler that generates better code
>than the competing compilers *AND* is FASTER than it's previous version?

I believe that relatively simple compilers can run in time proportional to
the number N of statements being compiled, but that certain non-simple
classes of optimization require execution time that is O(N log N) or perhaps
even O( N ** 1.5 ).

If I am right, then for sufficiently large program size (probably that means
"sufficiently large function size" in the case of C or of other languages
that support completely independent compilation of functions), a "simple"
compiler will compile arbitrarily faster than one which does these
optimizations.

Note also that if I am right, then if a software manufacturer truthfully
states "our product will compile at the rate of N lines per minute",
independently of program size, then that manufacturer is admitting to the
world at large that the product CANNOT generate first-rate code.

<canonical disclaimer -- these are personal opinions only>