Strange optimization in GCC 4.7.2

[David Given]

Konstantin Vladimirov wrote:
[...]
> x = (y & ~(1 << 7)) | (((value >> 9) & 1) << 7);
[...]
> x = y & 4294967167 | (value >> 9) << 7 & 255; <--------- WAT?


   ((value >> 9) & 1) << 7
== ((value >> 9) << 7) & (1 << 7)
== ((value >> 9) << 7) & 0x80
== ((value >> 9) << 7) & 0xff

...I think.

That last step is probably being done because anding with 0xff is really
cheap on x86 (you just pick the appropriate subreg --- al instead of
eax, for example).

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