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Re: [PATCH] x86_64: Remove 9 REX bytes from memchr.S
On Sat, May 20, 2017 at 7:59 AM, Zack Weinberg <zackw@panix.com> wrote:
> On Sat, May 20, 2017 at 10:50 AM, H.J. Lu <hongjiu.lu@intel.com> wrote:
>> There is no need to use 64-bit registers when only the lower 32 bits
>> are non-zero.
>
> This code is used generically for x86-64, not for a specific
> microarchitecture. Is there a reason why this will never cause partial
> register stalls, now or in the future?
By x86-64 specification, 32-bit destination registers in these instructions
are zero-extended to 64 bits and there is register stall at all.
--
H.J.