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Subject: [Bug tree-optimization/56175] Issue with combine phase on x86.
Date: Mon, 11 Feb 2013 14:38:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56175

--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> 2013-02-11 14:38:37 UTC ---
(In reply to comment #5)
> This pattern is already recognized by simplify_bitwise_binary but only for
> usual int type, i.e. if we change all short types to the ordinary int (or
> unsigned) this simplification takes place (dump after 1st forwprop):
> 
>   <bb 4>:
>   x_8 = x_2(D) >> 1;
>   y_9 = y_4(D) >> 1;
>   _10 = x_8 & 1;
>   _11 = y_9 & 1;
>   _16 = x_8 ^ y_9;
>   z_12 = _16 & 1;
> 
> i.e. the issue is redundant type conversions:
> 
>   <bb 3>:
>   x_7 = x_2(D) >> 1;
>   y_8 = y_4(D) >> 1;
>   _13 = x_7 & 1;
>   _9 = (signed char) _13;
>   _14 = y_8 & 1;
>   _10 = (signed char) _14;
>   _11 = _9 ^ _10;
> 
> I assume that if we delete these redundant conversions the required
> simplification will happen.

Ah, well.  The issue is that we transformed (unsigned char)y & 1
to (unsigned char)(y & 1).