From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from az33egw02.freescale.net (az33egw02.freescale.net [192.88.158.103]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "az33egw02.freescale.net", Issuer "Thawte Premium Server CA" (verified OK)) by ozlabs.org (Postfix) with ESMTPS id 3675CDE133 for ; Wed, 21 May 2008 08:16:13 +1000 (EST) Date: Tue, 20 May 2008 15:11:02 -0700 (PDT) From: Trent Piepho To: Andreas Schwab Subject: Re: [PATCH] [POWERPC] Improve (in|out)_beXX() asm code In-Reply-To: Message-ID: References: <1211316025-29069-1-git-send-email-tpiepho@freescale.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Cc: Scott Wood , linuxppc-dev@ozlabs.org, linux-kernel@vger.kernel.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Wed, 21 May 2008, Andreas Schwab wrote: > Trent Piepho writes: > >> For the LE versions, eventually they boil down to an asm that will look >> something like this: >> asm("sync; stwbrx %1,0,%2" : "=m" (*addr) : "r" (val), "r" (addr)); >> >> While not perfect, this appears to be the best one can do. The issue is >> that the "stwbrx" instruction only comes in an indexed, or 'x', version, in >> which the address is represented by the sum of two registers (the "0,%2"). >> Unfortunately, gcc doesn't have a constraint for an indexed memory >> reference. > > There is the "Z" constraint, which matches either an indirect or an > indexed memory address. That should fit here. This came up on the Freescale list. I should have put what I wrote there into my patch descrition: It's the _le versions that have a problem, since we can't get gcc to just use the register indexed mode. It seems like an obvious thing to have a constraint for, but I guess there weren't enough instructions that only come in 'x' versions to bother with it. There is a 'Z' constraint, "Memory operand that is an indexed or indirect from a register", but I tried it and it can use both "rb,ri" and "disp(rb)" forms. Actually, I'm not sure how 'Z' is any different than "m"?