Path: utzoo!mnetor!uunet!husc6!mit-eddie!bbn!rochester!crowl
From: crowl@cs.rochester.edu (Lawrence Crowl)
Newsgroups: comp.lang.misc
Subject: Re: Displays (Was:  Var scoping in Wirth-type languages)
Message-ID: <7629@sol.ARPA>
Date: 11 Mar 88 20:32:01 GMT
References: <3821@ihlpf.ATT.COM> <2791@enea.se> <3949@ihlpf.ATT.COM> <7562@sol.ARPA> <4426@june.cs.washington.edu>
Reply-To: crowl@cs.rochester.edu (Lawrence Crowl)
Organization: U of Rochester, CS Dept, Rochester, NY
Lines: 21

In article <4426@june.cs.washington.edu> pardo@uw-june.UUCP
(David Keppel) writes:
)(Paraphrasing) from compilers class:
)
)    "Displays are a really great idea, but are too expensive to
)    implement to be useful for Algol-class languages."
)
)Where "too expensive" is measured in terms of the cost of maintaining
)one over each procedure call versus the performance penalty for scanning
)up the dynamic links.

Displays require one more load-to-register to implement than do static chains.
(Assuming you have enough registers to implement the display.  Most new
processors do.)  Given this incremental cost, an average of less than ONE
non-local reference per procedure will pay for the cost of maintaining the
display.  To convince me that displays are not worth the cost, you must show
me hard data indicating that non-local references are not much used.
-- 
  Lawrence Crowl		716-275-9499	University of Rochester
		      crowl@cs.rochester.edu	Computer Science Department
...!{allegra,decvax,rutgers}!rochester!crowl	Rochester, New York,  14627