[PATCH] Modularizing LICM

[Ashutosh Nema]

Hi reames, bruno,

LICM has ‘SinkRegion’, ‘HoistRegion’, ‘PromoteAliasSet’ as core features.
Currently these core features are tied up with LICM pass.
If someone wants any of these feature then he has to schedule LICM as a complete pass.
Also there is no way to call any of these feature in a pass.

This change is to expose LICM core functionalities as a utility.

Following is high level description of changes:

1) Added declaration of ‘SinkRegion’, ‘HoistRegion’ and ‘PromoteAliasSet’ in ‘LoopUtils.h’

2) Following members functions of LICM has moved out of class and marked as static functions.
     ‘inSubLoop’, ‘isNotUsedInLoop’, ‘canSinkOrHoistInst’, ‘hoist’, ‘sink’, ‘CloneInstructionInExitBlock’
     ‘isSafeToExecuteUnconditionally’, ‘pointerInvalidatedByLoop’, ‘isGuaranteedToExecute’

3) Updated these functions with their dependencies.

4) LICM pass is now more like a wrapper pass, calling SinkRegion, HoistRegion, PromoteAliasSet utility.

5) Caller to ‘SinkRegion’, ‘HoistRegion’ and ‘PromoteAliasSet should provide all the required arguments.

For now I kept everything to same LICM.cpp but later we can move ‘SinkRegion’, ‘HoistRegion’, 
‘PromoteAliasSet’ and helper functions to separate utility file (i.e. LICMCore.cpp)

Please review this change, suggestions are welcome.

REPOSITORY
  rL LLVM

http://reviews.llvm.org/D7291

Files:
  include/llvm/Transforms/Utils/LoopUtils.h
  lib/Transforms/Scalar/LICM.cpp

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