From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-return-104917-listarch-gcc=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 13291 invoked by alias); 3 Nov 2004 06:43:03 -0000
Mailing-List: contact gcc-help@gcc.gnu.org; run by ezmlm
Precedence: bulk
List-Archive: <http://gcc.gnu.org/ml/gcc/>
List-Post: <mailto:gcc@gcc.gnu.org>
List-Help: <http://gcc.gnu.org/ml/>
Sender: gcc-owner@gcc.gnu.org
Received: (qmail 13282 invoked from network); 3 Nov 2004 06:43:01 -0000
Received: from unknown (HELO balaji) (61.16.238.202)
  by sourceware.org with SMTP; 3 Nov 2004 06:43:01 -0000
Message-ID: <41887D89.4020109@acmet.com>
Date: Wed, 03 Nov 2004 06:43:00 -0000
From: Balaji S <sivanbalaji@acmet.com>
Organization: Acme Technologies Pvt. Ltd.
User-Agent: Mozilla Thunderbird 0.8 (Windows/20040913)
MIME-Version: 1.0
To:  gcc@gcc.gnu.org
Subject: Porting question: define_expand Vs define_split
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
X-SW-Source: 2004-11/txt/msg00110.txt.bz2

Hi all,
I am porting GCC to a new architecture using stormy16 as base.

In my architecture there is no instruction for /neg/ operation. So i planned to handle it using /sub/. I am able to accomplish this job by using either define_expand or define_split without knowing its internals as follows:

(define_expand "neghi2"
  [(set (match_operand:HI 0 "register_operand" "")
	(const_int 0))
   (set (match_dup 0)
	(minus:HI (match_dup 0)
		  (match_operand:HI 1 "register_operand" "")))]
  ""
  "")

(define_insn_and_split "neghi2"
  [(set (match_operand:HI 0 "register_operand" "=r")
	(neg:HI (match_operand:HI 1 "register_operand" "0")))]
  ""
  "#"
  "reload_completed"
  [(set (match_dup 0)
	(const_int 0))
   (set (match_dup 0)
	(minus:HI (match_dup 0)
		  (match_dup 1)))]
  "")

I do not know whether the above m/c descriptions are correct. Please correct me if any mistakes.

Moreover, i would like to know, when to use /define_expand/ and when to use /define_split/.


Thanks in advance,
Balaji S