linux-kernel - RE: [PATCH v3 2/2] powerpc: add support for csum

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Message-ID: <063D6719AE5E284EB5DD2968C1650D6D1CB3EB5F@AcuExch.aculab.com>
Date:	Tue, 26 May 2015 13:57:32 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Scott Wood' <scottwood@...escale.com>
CC:	'Christophe Leroy' <christophe.leroy@....fr>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	"Michael Ellerman" <mpe@...erman.id.au>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v3 2/2] powerpc: add support for csum_add()

From: Scott Wood ...
> > I'd also have thought that the 64bit C version above would be generally 'good'.
> 
> It doesn't generate the addc/addze sequence.  At least with GCC 4.8.2,
> it does something like:
> 
> 	mr	tmp0, csum
> 	li	tmp1, 0
> 	li	tmp2, 0
> 	addc	tmp3, addend, tmp0
> 	adde	csum, tmp2, tmp1
> 	add	csum, csum, tmp3

I was thinking of all 64bit targets, not 32bit ones.

	David