linux-kernel - Re: [PATCH 1/2] powerpc: rewrite LOAD_REG

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Message-ID: <20190814201042.GH31406@gate.crashing.org>
Date:   Wed, 14 Aug 2019 15:10:42 -0500
From:   Segher Boessenkool <segher@...nel.crashing.org>
To:     Christophe Leroy <christophe.leroy@....fr>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 1/2] powerpc: rewrite LOAD_REG_IMMEDIATE() as an intelligent macro

Hi Christophe,

On Tue, Aug 13, 2019 at 09:59:35AM +0000, Christophe Leroy wrote:
> +		rldicr	\r, \r, 32, 31

Could you please write this as
		sldi	\r, \r, 32
?  It's much easier to read, imo (it's the exact same instruction).

You can do a lot cheaper sequences if you have a temporary reg, as well
(longest path of 3 insns instead of 5):
	lis rt,A
	ori rt,B
	lis rd,C
	ori rd,D
	rldimi rd,rt,32,0
to load ABCD.


Segher