[cfe-dev] libc++abi

[David Chisnall]

On 24 May 2011, at 17:56, Chris Lattner wrote:

> The bulk of libcxxrt is an older demangler


This is incorrect.  The bulk of the code is the exception handling / RTTI logic - this is nontrivial to implement correctly and is invoked by a significant amount of C++ code, often on important code paths, while the demangler is largely used for debugging and error reporting (for example, in the uncaught exception handler).  

The demangler is from libelftc - we tried importing the demangler from libc++abi, but it turned out to increase the total object code size of libcxxrt by a factor of four, which is unacceptable for a core system library like this.  

We may replace the libelftc demangler with something else at some point, but the current code fits the requirements of libcxxrt:

- Lightweight
- Good performance
- Permissively licensed

If libelftc gains support for the C++0x extensions, then we will just import their code.  Otherwise, we will probably extend it ourselves and push the improvements upstream.  While I like Howard's interface to the demanger for use by clients such as debuggers that require rich introspection of C++ encodings, it is massively overengineered for use in a C++ runtime library, which just requires to dump the encodings into a string, with minimal space requirements (as one common use for this code is dumping a type when you have run out of memory).

David
(author of most of libcxxrt)

-- Send from my Jacquard Loom