H. Peter Anvin wrote:
>
> "I" is correct. The Intel documentation on this is highly confusing
> (and has bugs in it), but it does unambiguously state:
>
> "Some assemblers support immediate bit offsets larger than 31 by using
> the immediate bit offset field in combination with the displacement
> field in the memory operand ... The processor will ignore the high-order
> bits if they are not zero." AMD processors might be different for all I
> know.
>
> So unless gas is capable of doing this transformation (and it's not as
> of binutils-2.17.50.0.6) "I" is what's needed here.
>
Just tested it on a K8 machine; AMD behaves the same way. So "I" is
correct, and changing it to "N" would introduce a bug.
The only way to optimize this is by using __builtin_constant_p() and
adjust the offset appropriately.
-hpa
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