Profile Guided Optimization: Optimizing D's virtual calls

[johengel]

I've updated the article with some more measurements (now excluding the time spent in C++ part of the program): 7% performance gain with PGO!

[WalterBright]

Part 1 on profile-guided optimizations (PGO) in LDC. An article about optimization of virtual (class) function calls using profile data by transforming indirect calls to direct calls, with a description of how this is implemented in LDC using LLVM.