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From: brnstnd@kramden.acf.nyu.edu (Dan Bernstein)
Newsgroups: comp.lang.c
Subject: Re: low level optimization
Message-ID: <25371:Apr1907:22:5091@kramden.acf.nyu.edu>
Date: 19 Apr 91 07:22:50 GMT
References: <21660@lanl.gov> <15881@smoke.brl.mil> <21815@lanl.gov>
Organization: IR
Lines: 25

In article <21815@lanl.gov> jlg@cochiti.lanl.gov (Jim Giles) writes:
> You can tell me that until you are blue in the face.  I have never seen
> any of these hypothetical contexts in which anonymous pointer arguments
> passed in as parameters can be safely assumed not to be aliased.
> Please give an example.

(``Anonymous pointer arguments''?)

sort(table,records,n)
int *table;
struct blah *records;
int n;

This routine sorts n records, setting table[i] to the position of the
i'th smallest record. This is, in fact, a very common type of sort,
hardly a ``hypothetical'' or contrived example. I recommend that you
read Knuth to learn about sorting and its many applications.

Since neither ``int'' nor ``struct blah'' is ``char'' or ``void'', a
standard compiler may assume that the pointers are not aliased.

(I don't expect Jim to respond to this article; he always ignores
counterexamples.)

---Dan