Messages in this thread | | | Date | Tue, 26 Jun 2018 00:32:31 -0600 | From | "Jan Beulich" <> | Subject | Re: [PATCH] x86-64: use 32-bit XOR to zero registers |
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>>> On 25.06.18 at 18:33, <rdunlap@infradead.org> wrote: > On 06/25/2018 03:25 AM, Jan Beulich wrote: >> Some Intel CPUs don't recognize 64-bit XORs as zeroing idioms - use >> 32-bit ones instead. > > Hmph. Is that considered a bug (errata)?
No.
> URL/references?
Intel's Optimization Reference Manual says so (in rev 040 this is in section 16.2.2.5 "Zeroing Idioms" as a subsection of the Goldmont/Silvermont descriptions).
> Are these changes really only zeroing the lower 32 bits of the register? > and that's all that the code cares about?
No - like all operations targeting a 32-bit register, the result is zero extended to the entire 64-bit destination register.
Jan
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