According to this study long-term cannabis use has little effect on cognitive function. Of course you’ll have to pay to read the fucking study, but hey at least Time did a nice little write-up about it, which I’m guessing better tuned to your short attention span anyhow.
The gist of the study is that 2000 Australian men and women were studied for a period of 8 years. Periodically the participants were given exams to test their cognitive abilities. Participants were also asked to volunteer information about their usage habits.
With this information I hope that you will now feel free to continue your weed smoking unencumbered by fear of cognitive attenuation.