linux-kernel - Re: [PATCH] MIPS: crypto: Clean up useless assignment operations

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Date: Fri, 28 Jun 2024 17:42:51 +0100 (BST)
From: "Maciej W. Rozycki" <macro@...am.me.uk>
To: WangYuli <wangyuli@...ontech.com>
cc: herbert@...dor.apana.org.au, linux-crypto@...r.kernel.org, 
    linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org, 
    Guan Wentao <guanwentao@...ontech.com>, 
    "David S. Miller" <davem@...emloft.net>, 
    Thomas Bogendoerfer <tsbogend@...ha.franken.de>
Subject: Re: [PATCH] MIPS: crypto: Clean up useless assignment operations

On Fri, 28 Jun 2024, WangYuli wrote:

> As you can see, regardless of the Clang or GCC version, this redundant
> operation affects the generated
> 
> assembly code.

 Boy, this code is horribly structured!

 Anyway, rather than making it yet worse with another #ifdef I'd suggest 
replacing both `while' loops with equivalent `for' ones with `len' being 
the worker variable, which will then make the code structure a little bit 
better and as a side effect address the missed optimisation automagically.

 You might also consider Herbert's suggestion to use IS_ENABLED, however 
in the current shape of code I find it kind of pointless anyway.  Instead 
I think that it would make more sense to factor out the block bodies to 
small static inline helpers and then restructure the call sites so that 
IS_ENABLED controls the loops, the conditionals, and the choice between 
them as applicable.

  Maciej