Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!umich!yale!cmcl2!stealth.acf.nyu.edu!brnstnd
From: brnstnd@stealth.acf.nyu.edu
Newsgroups: comp.lang.c
Subject: When should variables within blocks be allocated?
Message-ID: <26449@stealth.acf.nyu.edu>
Date: 18 Jan 90 22:17:33 GMT
References: <253@usblues.UUCP>
Reply-To: brnstnd@stealth.acf.nyu.edu (Dan Bernstein)
Distribution: usa
Organization: IR
Lines: 15
X-Original-Subject: Re: Is goto safe?

In article <253@usblues.UUCP> tom@usblues.UUCP (Tom Markson) writes:
> The .s file indicates that all stack space is allocated at the start of a 
> function.  

If a function contains the statement if(0) { int k[100000000]; ... },
should the space for k be allocated? Every compiler I've tried allocates
variables at function entry like Tom's, but it would be nice to save
100M of memory if k is never used. I can't find any ANSI rules on this.

If the answer is that the space for k can be ignored, are there any
compilers smart enough to optimize k away? Are there any compilers that
go all the way and allocate k the moment they enter the block? Is the
space saved worth the efficiency loss?

---Dan