1Itanium Name Demangler Library
2==============================
3
4Introduction
5------------
6
7This directory contains the generic itanium name demangler
8library. The main purpose of the library is to demangle C++ symbols,
9i.e. convert the string "_Z1fv" into "f()". You can also use the CRTP
10base ManglingParser to perform some simple analysis on the mangled
11name, or (in LLVM) use the opaque ItaniumPartialDemangler to query the
12demangled AST.
13
14Why are there multiple copies of the this library in the source tree?
15---------------------------------------------------------------------
16
17The canonical sources are in libcxxabi/src/demangle and some of the
18files are copied to llvm/include/llvm/Demangle.  The simple reason for
19this comes from before the monorepo, and both [sub]projects need to
20demangle symbols, but neither can depend on each other.
21
22* libcxxabi needs the demangler to implement __cxa_demangle, which is
23  part of the itanium ABI spec.
24
25* LLVM needs a copy for a bunch of places, and cannot rely on the
26  system's __cxa_demangle because it a) might not be available (i.e.,
27  on Windows), and b) may not be up-to-date on the latest language
28  features.
29
30The copy of the demangler in LLVM has some extra stuff that aren't
31needed in libcxxabi (ie, the MSVC demangler, ItaniumPartialDemangler),
32which depend on the shared generic components. Despite these
33differences, we want to keep the "core" generic demangling library
34identical between both copies to simplify development and testing.
35
36If you're working on the generic library, then do the work first in
37libcxxabi, then run the cp-to-llvm.sh script in src/demangle. This
38script takes as an optional argument the path to llvm, and copies the
39changes you made to libcxxabi over.  Note that this script just
40blindly overwrites all changes to the generic library in llvm, so be
41careful.
42
43Because the core demangler needs to work in libcxxabi, everything
44needs to be declared in an anonymous namespace (see
45DEMANGLE_NAMESPACE_BEGIN), and you can't introduce any code that
46depends on the libcxx dylib.
47
48FIXME: Now that LLVM is a monorepo, it should be possible to
49de-duplicate this code, and have both LLVM and libcxxabi depend on a
50shared demangler library.
51
52Testing
53-------
54
55The tests are split up between libcxxabi/test/{unit,}test_demangle.cpp, and
56llvm/unittest/Demangle. The llvm directory should only get tests for stuff not
57included in the core library. In the future though, we should probably move all
58the tests to LLVM.
59
60It is also a really good idea to run libFuzzer after non-trivial changes, see
61libcxxabi/fuzz/cxa_demangle_fuzzer.cpp and https://llvm.org/docs/LibFuzzer.html.
62