Log Message:
Changes 3.9.1:
The LLVMContext gains a new runtime check (see LLVMContext::discardValueNames()) \ 
that can be set to discard Value names (other than GlobalValue). This is \ 
intended to be used in release builds by clients that are interested in saving \ 
CPU/memory as much as possible.
There is no longer a “global context” available in LLVM, except for \ 
the C API.
The autoconf build system has been removed in favor of CMake. LLVM 3.9 requires \ 
CMake 3.4.3 or later to build. For information about using CMake please see the \ 
documentation on Building LLVM with CMake. For information about the CMake \ 
language there is also a CMake Primer document available.
C API functions LLVMParseBitcode, LLVMParseBitcodeInContext, \ 
LLVMGetBitcodeModuleInContext and LLVMGetBitcodeModule having been removed. \ 
LLVMGetTargetMachineData has been removed (use LLVMGetDataLayout instead).
The C API function LLVMLinkModules has been removed.
The C API function LLVMAddTargetData has been removed.
The C API function LLVMGetDataLayout is deprecated in favor of LLVMGetDataLayoutStr.
The C API enum LLVMAttribute and associated API is deprecated in favor of the \ 
new LLVMAttributeRef API. The deprecated functions are LLVMAddFunctionAttr, \ 
LLVMAddTargetDependentFunctionAttr, LLVMRemoveFunctionAttr, LLVMGetFunctionAttr, \ 
LLVMAddAttribute, LLVMRemoveAttribute, LLVMGetAttribute, LLVMAddInstrAttribute, \ 
LLVMRemoveInstrAttribute and LLVMSetInstrParamAlignment.
TargetFrameLowering::eliminateCallFramePseudoInstr now returns an iterator to \ 
the next instruction instead of void. Targets that previously did MBB.erase(I); \ 
return; now probably want return MBB.erase(I);.
SelectionDAGISel::Select now returns void. Out-of-tree targets will need to be \ 
updated to replace the argument node and remove any dead nodes in cases where \ 
they currently return an SDNode * from this interface.
Added the MemorySSA analysis, which hopes to replace MemoryDependenceAnalysis. \ 
It should provide higher-quality results than MemDep, and be algorithmically \ 
faster than MemDep. Currently, GVNHoist (which is off by default) makes use of \ 
MemorySSA.
The minimum density for lowering switches with jump tables has been reduced from \ 
40% to 10% for functions which are not marked optsize (that is, compiled with \ 
-Os).