Agner`s CPU blog

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Latency of PTEST/VPTEST
Author: Agner Date: 2014-05-20 06:23
It is impossible to measure the latency of an instruction with one type of registers as input (here YMM) and another type of registers as output (here flags). It is only possible to measure the round trip latency of a series of instructions ending with the same type of registers as it started with. The fact that the upper and lower half of a 256-bit register may have different latencies makes this even more difficult. I will have to improve the measurement of VPTEST in the next round of tests, but it is probably right that PTEST has higher latency for YMM registers than for XMM registers.
 
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