See test/Regression/ExecutionEngine/2005-12-02-TailCallBug.ll

After a callback (for lazy compilation), the execution engine would crash in JITCompilerFn(). Looks like the 
stub to function look up failed (it actually crashed during the map look up):
   // The address given to us for the stub may not be exactly right, it might be
  // a little bit after the stub.  As such, use upper_bound to find it.
  std::map<void*, Function*>::iterator I =
    JR.state.getStubToFunctionMap(locked).upper_bound(Stub);

This appears to be working now, I can't reproduce the crash with the new front
end and TOT llvm.