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From: Arnd Bergmann <arnd@arndb.de>
To: Tomas Winkler <tomasw@gmail.com>
Cc: "Levy, Amir (Jer)" <amir.jer.levy@intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
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Subject: Re: [PATCH v2] byteswap: try to avoid __builtin_constant_p gcc bug
Date: Wed, 22 Jun 2016 14:25:11 +0200
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On Wednesday, June 22, 2016 2:44:21 PM CEST Tomas Winkler wrote:
> >
> > There are more than 20 files that have the statement: case cpu_to_...
> > Sparse complains about: case __builtin_bswap, not about __builtin_constant_p.
> 
> There is even much more in the header files used in  initializers,
> which also require constants.  I wonder if __builtin_bswap produces
> constant expression correctly under gcc?

In gcc-4.8 or later yes. gcc-4.6/4.7 on powerpc was a special case that we
have worked around now, as the 16-bit byteswap there was not a constant
expression, unlike the 32-bit and 64-bit ones.

	Arnd