Path: utzoo!utgpu!jarvis.csri.toronto.edu!white.toronto.edu!cks
Newsgroups: comp.lang.misc
From: cks@white.toronto.edu (Chris Siebenmann)
Subject: Re: 'register' variables and other goodies (was Re: Common subexpression optimization)
Message-ID: <1990Feb12.172948.17784@jarvis.csri.toronto.edu>
References: <1624@aber-cs.UUCP>
Date: 12 Feb 90 22:29:48 GMT
Lines: 30

pcg@cs.aber.ac.uk (Piercarlo Grandi) writes:
| Compilers that can do a good job should either use heuristics, or
| profile feedback, and are exceedingly rare. In both cases the
| compiler becomes more complex (becomes it has to analyze control and
| data flows as a preliminary -- it is this that makes the compiler
| more complex, not the optimization per se).

 Profiling feedback compilers are becoming more and more common and at
least one set are fairly widely used: the MIPSco compilers. As people
start reading various technical reports about the gains possible and
become more aware of the usefulness of this sort of thing.

| I think that the programmer, *by design* (aided by heuristics and
| profiling, yes) should know what is going on, and tell the compiler
| instead.

 I agree that programmers should have some way of manually telling the
compiler about usage frequency. However, given that we're already
assuming a profiler at work, and the usual quality of commercial
programmers, I think it's foolish not to let the compiler/linker read
the profiling results directly. When something is simple and
mechanical, why not let the computer do the drudge work?

 I wonder how many programmers even bother running a profiler on their
programs? I suspect not many.

--
	"I shall clasp my hands together and bow to the corners of the world."
			Number Ten Ox, "Bridge of Birds"
cks@white.toronto.edu		   ...!{utgpu,utzoo,watmath}!utcsri!white!cks