[llvm] r210641 - Create macro INITIALIZE_TM_PASS.

[Rafael Espíndola]

> I think we're mixing concepts up here. Sorry I didn't jump on the earlier
> review thread.
>
> The key is that we *really must not* add more passes to lib/Transforms which
> accept a TargetMachine. We can still have plenty of IR-operating passes in
> lib/CodeGen that take a TargetMachine, that's fine. If you want to have a
> macro to automate it, put it in include/llvm/CodeGen/CodeGenPassSupport.h or
> some other *clearly* backend header file so that it is really obvious that
> it should not be used in purportedly target-independent passes.
>
> TargetTransformInfo is a generic interface by which a target can expose
> information to a lib/Transform pass. This allows truly target independent
> passes to be tested without even having a target around because the
> interface they use to communicate with the target is very nicely abstracted.
> But there are plenty of passes which really aren't that target independent,
> and those should just stay in lib/CodeGen.
>
> AFAIK, CodeGenPrep is the only pass that violates these principles today. I
> think it should just be moved to lib/CodeGen personally, but haven't worked
> with it enough to really tell whether it should instead be reduced to use a
> easily abstracted interface like TargetTransformInfo.

OK, that makes sense.

Jiangning, can you move the macro to some header in
include/llvm/CodeGen and figure out if GlobalMerge.cpp should move to
lib/CodeGen or be implemented on top of TargetTransformInfo?

Thanks,
Rafael