SSE42 & STTNI - PcmpEstrM is twice slower than PcmpIstrM, is it true?

Question

I\'m experimenting with SSE42 and STTNI instructions and have got strange result - PcmpEstrM (works with explicit length strings) runs twice slower

Answer 1

According to the instruction tables of Agner fog, pcmpestrm takes 8 µops, whereas pcmpistrm takes 3 µops on most architectures. This should explain the performance difference you observe. Consider rewriting your code so you can use pcmpistrm instead of pcmpestrm if possible.