[llvm-dev] RFC: Improving the performance of ItaniumDemangle

Vedant Kumar via llvm-dev llvm-dev at lists.llvm.org
Tue Apr 25 12:19:51 PDT 2017

I thought the plan of record was (r280732):

Once the fast demangler in lldb can handle any names this 
implementation can be replaced with it and we will have the one true 

What is the status of lldb's fast demangler? Is it available on Ubuntu 16.04?


> On Apr 24, 2017, at 6:02 PM, Scott Smith via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> (Again), while trying to improve the performance of lldb, I ran into a bottleneck with the demangler.  This may be specific to my platform - Ubuntu 16.04, probably using libstdc++, not libc++.  It makes extensive use of std::string and std::vector, and I see memory allocation at the top.  I prototyped a version that uses an arena-style memory allocator (you can allocate, but you can't ever free).  It is approximately 14+% faster.  I think I can further optimize it by making repeated appends zero-copy (for the string being appended too).
> The code right now is a little ugly, because it uses a thread local variable to pass around the arena pointer, rather than change every + and += to be function calls that take db.arena as a parameter.  I'm not sure what you guys would prefer for that either (thread local variable vs api change).
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