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From: ark@alice.UucP (Andrew Koenig)
Newsgroups: net.lang
Subject: Re: Recursion
Message-ID: <4302@alice.UUCP>
Date: Wed, 11-Sep-85 16:15:16 EDT
Article-I.D.: alice.4302
Posted: Wed Sep 11 16:15:16 1985
Date-Received: Thu, 12-Sep-85 11:50:43 EDT
References: <250@mot.UUCP>
Organization: Bell Labs, Murray Hill
Lines: 13

>>     I think that would be a good idea, but wouldnt it be limited to direct
>> recursion ( i.e. routine A calls A as apposed to A calls B, B calls A ). I
>> don't know PL/I, but I would think including such a check for anything other
>> than direct recursion would be a royal pain for a compiler writter.
>> 
> Actually, it's not too bad.  You just set up an n-by-n Boolean matrix
> where n is the number of subroutines under consideration and the
> ij element is 1 iff routine i calls routine j.  Then take the
> transitive closure by Warshall's algorithm.  1's on the diagonal of
> the result indicate which routines are indirectly recursive.

This uses up memory proportional to the square of the
number of subroutines.  Not a good idea.