linux-kernel - Re: [PATCH] UBIFS: endian handling fixes and annotations

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Message-ID: <20081123100534.GB29843@shareable.org>
Date:	Sun, 23 Nov 2008 10:05:34 +0000
From:	Jamie Lokier <jamie@...reable.org>
To:	Sebastian Andrzej Siewior <sebastian@...akpoint.cc>
Cc:	Artem Bityutskiy <dedekind@...radead.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] UBIFS: endian handling fixes and annotations

Sebastian Andrzej Siewior wrote:
> >-	return le32_to_cpu(key->u32[1]) >> UBIFS_S_KEY_BLOCK_BITS;
> >+	return le32_to_cpu(key->j32[1]) >> UBIFS_S_KEY_BLOCK_BITS;
> 
> If you would change such references to something like
> |return le32_to_cpup(&key->j32[1]) >> UBIFS_S_KEY_BLOCK_BITS;
> then on powerpc
> 
>   text    data     bss     dec     hex filename
> 155384    1284      24  156692   26414 ubifs-b4.ko
> 155372    1284      24  156680   26408 ubifs-after.ko
> 
> because now it is possible to load the value as LE from memory instead
> of loading it BE and swapping it afterwads.

If le32_to_cpu used __builtin_bswap32 (a GCC builtin), wouldn't
GCC do this trivial optimisation itself?

-- Jamie
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