I’ve found that one of the most useful tools in the Chromium project is its code search website, http://cs.chromium.org/
At http://llvm-cs.pcc.me.uk/ you will find something similar for llvm. You can search the full text of the llvm/clang/lld/lldb repositories using regular expressions, search for declarations (which are prioritized above full-text results), and follow cross references between definitions and references.
The code behind this website is based on kythe  (Kythe itself uses the clang libraries to parse C++ code) and Russ Cox’s codesearch  library. I’m planning to open source it and contribute it to the kythe project.
I like Kythe and this approach, but you may want to check DXR  that
is similar (with a little nicer interface). Browse Firefox's code with
DXR to feel what it's like .
The approach is basically building the project while building all the
information+references. It's adding plugins for more languages too
(other than C/C++).
 / - mozsearch
Thanks. I was aware of DXR, but I didn’t know that they were using Clang. Kythe uses a similar approach, but there’s no need to actually build the whole project, you just need a compilation database . In LLVM’s case, I need to arrange to build all the tablegen’d files upfront, and I have a hacky script that does so by parsing the “ninja -t commands” output.
Nice! Glad to see some work progressing on a UI