SCEVRewriter: Optionally interpret constants in value map as SCEVConstant
SCEVRewriter: Optionally interpret constants in value map as SCEVConstant

An upcoming loop vectorizer commit will want to replace a SCEVUnknown(Value*)
by a SCEVConstant. This commit modifies the SCEVParameterRewriter to support
this. The SCEVParameterRewriter constructor can optionally specify to follow
this behavior.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@198949 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/llvm,apple/swift-llvm,apple/swift-llvm,chubbymaggie/asap,chubbymaggie/asap,dslab-epfl/asap,apple/swift-llvm,GPUOpen-Drivers/llvm,dslab-epfl/asap,GPUOpen-Drivers/llvm,apple/swift-llvm,llvm-mirror/llvm,dslab-epfl/asap,chubbymaggie/asap,apple/swift-llvm,apple/swift-llvm,dslab-epfl/asap,GPUOpen-Drivers/llvm,llvm-mirror/llvm,chubbymaggie/asap,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,dslab-epfl/asap,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,llvm-mirror/llvm,dslab-epfl/asap,chubbymaggie/asap,llvm-mirror/llvm,dslab-epfl/asap,GPUOpen-Drivers/llvm,apple/swift-llvm,chubbymaggie/asap,GPUOpen-Drivers/llvm