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This frees the Cmm data type from keeping a list of live global registers
in CmmCall which helps prepare for the CPS conversion phase.

CPS conversion does its own liveness analysis and takes input that should
not directly refer to parameter registers (e.g. R1, F5, D3, L2).  Since
these are the only things which could occur in the live global register
list, CPS conversion makes that field of the CmmCall constructor obsolite.

Once the CPS conversion pass is fully implemented, global register saving
will move from codeGen into the CPS pass.  Until then, this patch
is worth scrutinizing and testing to ensure it doesn't cause any performance
or correctness problems as the code passed to the backends by the CPS
converting will look very similar to the code that this patch makes codeGen
pass to the backend.

Since a CmmCall returns CmmFormals which may include
global registers (and indeed one place in the code
returns the results of a CmmCall into BaseReg) and
since CPS conversion will change those return slots
into formal arguments for the continuation of the call,
CmmProc has to have CmmFormals for the formal arguments.

Oddly, the old code never made use of procedure arguments
so this change only effects the types and not any of the code.
(Because [] is both of type [LocalReg] and CmmFormals.)

The function
  listSplitUniqSupply :: UniqSupply -> [UniqSupply]
splits a UniqSupply into an infinite list of supplies.
It is a generalization of splitUniqSupply.

This is a safety check-in, before I begin a cleanup.

At present it just annotates each block with a comment
indicating what local registers are live at the start
of the block.

Dataflow.hs contains an early draft of the live variable analysis.
This draft contains known bugs and is being recorded only to provide
a point to be revert back to if necessary.

See Note [Recursive rules] in OccurAnal

Fans of the banner can add
    putStrLn "   ___         ___ _"
    putStrLn "  / _ \\ /\\  /\\/ __(_)"
    putStrLn " / /_\\// /_/ / /  | |   GHC Interactive, for Haskell 98."
    putStrLn "/ /_\\\\/ __  / /___| |   http://www.haskell.org/ghc/"
    putStrLn "\\____/\\/ /_/\\____/|_|   Type :? for help."
    putStrLn ""
to their ~/.ghci

The logic for printing the ghc and ghci usage messages was inverted.
However, the ghci case will never actually happen with the current code,
as we print a usage message when cli_mode == ShowUsage and choose the
ghci usage message if cli_mode == DoInteractive. This should be fixed
as part of a larger options handling overhaul.