>>> On 25.06.18 at 18:33, <rdun...@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
