title: Missing latency in instruction tables
body: <p>I am currently looking at Agner Fog's <a href="https://www.agner.org/optimize/instruction_tables.pdf" rel="nofollow noreferrer">instruction tables</a> to get an idea of the latencies of common instructions.</p>
  
  <p>I hope I haven't missed the answer of this question in the documents, but can anyone explain to me why for some instructions, there is no latency entry?</p>
  
  <p>For example, the latency for the PEXT instructions, with operands r,r,m, is left blank for Skylake?</p>
  
  <p>What is the interpretation for the missing latency and why is it difficult to get the latency in the first place (if this is the case) ?</p>