From: Troy VanHorn <trvanhor AT UCollege DOT edu>
Message-Id: <199809010109.UAA05151@snoopy.UCollege.edu>
Subject: Re: passing arguments in registers
To: GAMMELJL AT SLU DOT EDU
Date: Mon, 31 Aug 1998 20:09:43 -0500 (CDT)
Cc: trvanhor AT snoopy DOT UCollege DOT edu (Troy VanHorn), djgpp AT delorie DOT com
In-Reply-To: <01J19GJU8Q9U94JXNE@SLU.EDU> from "GAMMELJL@SLU.EDU" at Aug "31," 1998 "06:04:28" pm
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> The following C/C++ code when compiled:
>                 gxx example9.cc -S -O2
> results in the .s file below it.  It is plain that the arguments
> of zadd are passed on the stack.  Eli Zareteskii has told me that
> passing them in registers requires
>                  __attribute__((regparm=2))

     Actually, you can make gcc pass up to three arguments in registers with
__attribute__((regparm=3)).


> and that the information about this is in the GCC docs.  Please:
> someone expert in searching these docs tell me exactly where this
>attribute statement goes in the C++ code below and exactly what the
>correct syntax is.

_____The C/C++ source code_(Modified)______________________________

int zadd(int m,int n)  __attribute__((regparm=3)); /* This should work */
int i,j,k;                       
                                 
main()
 {i=2;          /* ------> adds 2 and 3. */
  j=3;
  k=zadd(i,j);
  return 0;
 }

int zadd(int m,int n)  /* --------> one wishes to place the attriute
statement */
  {return m+n;}             /*  in this subroutine */

----------------
Troy Van Horn