[LLVMdev] Improving performance with optimization passes

[Jon Harrop]

I'm toying with benchmarks on my HLVM and am unable to get any performance 
improvement from optimization passes. Moreover, some of my programs generate 
a lot of redundant code (e.g. alloca a struct, store a struct into it and 
read only one field without using the rest of the struct) and this does not 
appear to be optimized away.

I simply copied the use of PassManager from the Kaleidoscope tutorial:

  let pm = PassManager.create_function mp in
  TargetData.add (ExecutionEngine.target_data ee) pm;

  add_constant_propagation pm;

  (* Do simple "peephole" optimizations and bit-twiddling optzn. *)
  add_instruction_combining pm;

  (* reassociate expressions. *)
  add_reassociation pm;

  (* Eliminate Common SubExpressions. *)
  add_gvn pm;

  (* Simplify the control flow graph (deleting unreachable blocks, etc). *)
  add_cfg_simplification pm;

  add_memory_to_register_promotion pm;

and then I apply "PassManager.run_function" to every function after it is 
validated.

Any idea what I might be doing wrong? Has anyone else got this functionality 
giving performance boosts from OCaml?

-- 
Dr Jon Harrop, Flying Frog Consultancy Ltd.
http://www.ffconsultancy.com/?e