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Re: [PATCH v2] byteswap: try to avoid __builtin_constant_p gcc bug

From Arnd Bergmann <arnd@arndb.de>
Newsgroups linux.kernel
Subject Re: [PATCH v2] byteswap: try to avoid __builtin_constant_p gcc bug
Date 2016-06-22 14:40 +0200
Message-ID <rMPBM-3lU-9@gated-at.bofh.it> (permalink)
References <rutT5-3cr-19@gated-at.bofh.it> <rMNJD-2bS-3@gated-at.bofh.it> <rMOPn-2Q3-9@gated-at.bofh.it>
Organization linux.* mail to news gateway

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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

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Re: [PATCH v2] byteswap: try to avoid __builtin_constant_p gcc bug Tomas Winkler <tomasw@gmail.com> - 2016-06-21 11:20 +0200
  Re: [PATCH v2] byteswap: try to avoid __builtin_constant_p gcc bug Tomas Winkler <tomasw@gmail.com> - 2016-06-22 10:40 +0200
    Re: [PATCH v2] byteswap: try to avoid __builtin_constant_p gcc bug Arnd Bergmann <arnd@arndb.de> - 2016-06-22 12:20 +0200
      RE: [PATCH v2] byteswap: try to avoid __builtin_constant_p gcc bug "Levy, Amir (Jer)" <amir.jer.levy@intel.com> - 2016-06-22 12:40 +0200
        Re: [PATCH v2] byteswap: try to avoid __builtin_constant_p gcc bug Tomas Winkler <tomasw@gmail.com> - 2016-06-22 13:50 +0200
          Re: [PATCH v2] byteswap: try to avoid __builtin_constant_p gcc bug Arnd Bergmann <arnd@arndb.de> - 2016-06-22 14:40 +0200
            Re: [PATCH v2] byteswap: try to avoid __builtin_constant_p gcc bug Tomas Winkler <tomasw@gmail.com> - 2016-06-23 08:30 +0200
              Re: [PATCH v2] byteswap: try to avoid __builtin_constant_p gcc bug Arnd Bergmann <arnd@arndb.de> - 2016-06-23 11:30 +0200

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