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Date: Fri, 24 Oct 2003 13:49:00 -0000
From: Gunther Nikl <gni@gecko.de>
To: Bernardo Innocenti <bernie@develer.com>
Cc: GCC Mailing List <gcc@gcc.gnu.org>
Subject: Re: Testing m68k changes on AmigaOS and Linux/m68k
Message-ID: <20031024120720.GA30830@lorien.int.gecko.de>
References: <3F8C28AE.4060301@develer.com> <20031015093247.GA41502@lorien.int.gecko.de> <20031015164848.GA7684@lorien.int.gecko.de> <3F8D97C6.5020406@develer.com> <20031016133157.GA14232@lorien.int.gecko.de> <3F8ECE9E.1080500@develer.com> <20031021120030.GA31365@lorien.int.gecko.de> <3F9570DD.4050700@develer.com> <20031023131324.GA28408@lorien.int.gecko.de> <3F981300.9030306@develer.com>
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On Thu, Oct 23, 2003 at 07:42:24PM +0200, Bernardo Innocenti wrote:
> Gunther Nikl wrote:
> >  The approach with the array is nasty :-/ Every usage of such macro
> >  will create a distinc array and this will eat up stackspace. Thats
> >  why I always disabled these macros.
> 
> I don't quite understand.  There's (almost) no difference in stack
                                      ^^^^^^
  Thats the import difference.

> space usage between this:
> 
>  {
>     int v[] = { 1, 2, 3, 4, 5 };
>     extern foo(int *);
>     foo(v);
>  }
> 
> ...and this:
> 
>  {
>     extern foo(...);
>     foo(1, 2, 3, 4, 5);
>  }
> 
> With the varargs form, the compiler will push all arguments on the
> stack before calling foo(), effectively wasting the same amount of
> stack space of the local array.

  The array is allocated at _frame generation_. Now imagine using a lot
  of such calls where every array is only used _one_ time. The varargs
  form uses the stackspace only temorary when making the call and cleans
  up soon after the call returns.

> When I had to pass a taglist made entirely of constant values, I used to
> do this instead:
> 
>   {
>      static const int tags[] = {...};
>      ...
>   }

  This is of course much better since the array is created a compile time
  and placed in readonly-memory.

  Gunther