Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!iuvax!ux1.cso.uiuc.edu!aries!mcdonald
From: mcdonald@aries.scs.uiuc.edu (Doug McDonald)
Newsgroups: comp.lang.c
Subject: Re: When should variables within blocks be allocated?
Message-ID: <1990Jan19.224633.22564@ux1.cso.uiuc.edu>
Date: 19 Jan 90 22:46:33 GMT
References: <253@usblues.UUCP> <26449@stealth.acf.nyu.edu>
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Organization: Univ. of Illinois at Urbana-Champaign, Chemical Sciences
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In article <26449@stealth.acf.nyu.edu> brnstnd@stealth.acf.nyu.edu (Dan Bernstein) writes:
>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.
>
I just tried it on the new compiler that arrived in the mail yesterday.

giving it the program

void sub() {
    while (0) {
        int j[1000000],i;
        for (i = 0; i < 1000000; i++) j[i] = i;
    }
} 


resulted in no data allocation and the generated code

ret

which is a pretty small function. MicroWay NDPC 2.00 for the 386.
Exchanging the while(0){ and int j[... lines gave the same result.

The VMS C compiler has been this good for quite a while.

Doug McDonald (mcdonald@aries.scs.uiuc.edu)