Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!usc!jarthur!uci-ics!gateway
From: rfg@paris.ics.uci.edu (Ronald Guilmette)
Newsgroups: gnu.gcc
Subject: A question on local variable allocation
Message-ID: <25E58087.11649@paris.ics.uci.edu>
Date: 23 Feb 90 18:27:19 GMT
Organization: UC Irvine Department of ICS
Lines: 43

Can someone please explain to me why, in the following code, the space
allocated for the two local array variables does not overlap?

Is there some little rule in the ANSI C standard that would require such
treatment?  It would seem to me that it is not necessary, and that it
can result in a waste of space, and also possibly slower execution
(due to increased paging and an increase in cache misses).

I am posting this question to gnu.gcc rather than the gnu.gcc.bug group
because this is *not* a bug.  The code certainly works "correctly" given
the allocation strategy that GCC is now exibiting.  My question is "Would
the code still work correctly even if GCC practiced overlaping allocation
for local variables in disjoint local scopes?"

If so, why has this not been implemented.  Superfically, it would seem to
be a simple thing to do.  (Of course I acknowledge that things always seem
that way as long as you are not the guy who has to roll up his sleeves and
get in and do it.)

(Note: In the following example, the function calls are only in there to
make sure that the arrays to not get optimized away entirely.)

	extern void g();

	void function ()
	{
	  {
	     int inside1[1024];

	     g (inside1);
	  }

	  {
	     int inside2[1024];

	     g (inside2);
	  }
	}


// Ron Guilmette (rfg@ics.uci.edu)
// C++ Entomologist
// Motto:  If it sticks, force it.  If it breaks, it needed replacing anyway.