[PATCH] Removing unnecessary addrspacecasts from non-generic address spaces to the generic address space

[Jingyue Wu]

Hi eliben, jholewinski,

This patch is the first step to implement the optimization we discussed in http://lists.cs.uiuc.edu/pipermail/llvmdev/2014-March/071440.html. It removes unnecessary casts from non-generic address spaces to the generic address space for certain code patterns. 

For now, we made the optimization specific to NVPTX. If you want to use it for other targets (e.g., R600), feel free to refactor it and we would be more than happy to review your change. 

Besides adding a new test (access-non-generic.ll), we modified addrspacecast.ll because llc now generates better code for some cases in it. 

http://llvm-reviews.chandlerc.com/D3235

Files:
  lib/Target/NVPTX/CMakeLists.txt
  lib/Target/NVPTX/NVPTX.h
  lib/Target/NVPTX/NVPTXFavorNonGenericAddrSpaces.cpp
  lib/Target/NVPTX/NVPTXTargetMachine.cpp
  test/CodeGen/NVPTX/access-non-generic.ll
  test/CodeGen/NVPTX/addrspacecast.ll
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