The compiler team hangs out primarily in the rust-lang Zulip
these days. The #t-compiler/help stream is a great place to ask
questions. In addition, each working group has 1 or more streams where
they communicate.
You can also find us on the rust-lang Discord, in the #compiler
channel.
The #rustc IRC channel on irc.mozilla.org is in a
"quasi-deprecated" status and is not recommended.