It's on the apple music page. iTunes match is built into Apple Music.
How does Apple Music know what songs are in my personal library?
With an Apple Music membership, your entire library lives in iCloud. We compare every track in your collection to the Apple Music library to see if we have a copy. If we do, you can automatically listen to it straight from the cloud. If you have music that’s not in our catalog, we upload those songs from iTunes on your Mac or PC. It’s all in iCloud, so it won’t take up any space on your devices.
It doesn't say anything about being able to upgrade and save your non-iTunes sourced old mp3s to a higher quality iTunes copy. You might be able to stream or download a copy with DRM for offline listening but nothing has been said about upgrading which is one of the big features of iTunes Match.