Add a fast-path for register values.  Add support for constant pool entries, allowing us to compile this:
Add a fast-path for register values.  Add support for constant pool entries,
allowing us to compile this:

float %test2(float* %P) {
        %Q = load float* %P
        %R = add float %Q, 10.1
        ret float %R
}

to this:

_test2:
        lfs r2, 0(r3)
        lis r3, ha16(.CPI_test2_0)
        lfs r3, lo16(.CPI_test2_0)(r3)
        fadds f1, r2, r3
        blr


git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@22962 91177308-0d34-0410-b5e6-96231b3b80d8

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