(1) Improved graph printing. Now, hierarchy of nodes is also generated in dot

file
(2) Fixed a bug in dfg2llvm-x86. Tests were crashing when input dimension to a
createNode1D/2D/3D intrinsic was a constant because of its absence in VMap. Now
fixed.
M    llvm/include/llvm/Support/DOTGraphTraits.h
M    llvm/include/llvm/Support/GraphWriter.h
M    llvm/include/llvm/IR/DFGraph.h
M    llvm/lib/Transforms/DFG2LLVM_X86/DFG2LLVM_X86.cpp