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SubjectRe: [PATCH 1/3] X86: Optimise fls(), ffs() and fls64()
Date
Avi Kivity <avi@redhat.com> wrote:

> Even if Intel processors behave that way, other processors (real and
> emulated) use those manuals as a specification. Emulated processors are
> unlikely to touch an undefined register, but real processors may.
>
> (qemu tcg appears not to touch the output)

Possibly because the AMD64 spec specifies that the destination will be
unchanged if the source was 0.

David


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