Refactor HPC support

[simonmar]

So we don't forget: as per discussion on cvs-ghc ( http://www.haskell.org/pipermail/cvs-ghc/2006-November/032434.html), look into refactoring the HPC support to use a PrimOp instead of a Note in Core.

[AndyGill]

The plan is to attempt to change to use of Note to hold ticks into using primops to represent ticks internally.

Simon suggested looking at the FCallId, as an example of how to have a primop like thing, but also have the primop "saturated with constants".

The will be done in late Nov or early Dec, 2006.

[AndyGill]

Completed this change. We no longer use Note, rather use

  case tick<mod,n> of
    _ -> ...

The generated code is the same boolean-wise as the old tick method.

• In some cases we generate better CAFs.
• The execution runtime is faster with -O2. (~50% faster on raytracer)
• The compile time is slower with -O2. (~50% slower, perhaps because of new optimizations kicking in)