you're right that shifts are affecting both 128-bit lanes (for _mm256... variants). I've checked our documentation and it's (only) mentioned incorrectly in the Intrinsics Guide for Intel Advanced Vector Extensions 2 (v2.6). I've filed a defect to fix that: DPD200272778.
Thank you for bringing this up!
Regarding the naming scheme: I don't see how your proposal would fit better, though. Post-fix si256 refers to the 256-bit size source vector register. That's still valid as we do 2x 128-bit value shifts. However, I agree that it's still a bit misleading... esp. for users who did not take a look a deeper look into the INTEL ADVANCED VECTOR EXTENSIONS (Ref. # 319433-011) document. In the end it's also a question how compact you'd like those intrinsic names to be. Describing (full) semantics in the name would be too much.
"Post-fix si256 refers to the 256-bit size source vector register."
Ah yes I missed the "si" vs "epi"thing,but since the "s" in si256 means "scalar"it gives the wrong impressionthat it shifta single value when it's in fact shifting independently two packed value
I you insist keeping it as is, something that will make some sensewill be to introducesome aliases called "_mm256_srli_epi128" and "_mm256_slli_epi128" ? I'm sure it will be quite more clear for newbies