Fix cases where we generated horrible code like this:

        mov %EDI, 12
        add %EDI, %ECX
        mov %ECX, 12
        add %ECX, %EDX
        mov %EDX, 12
        add %EDX, %ESI

instead (really!) generate this:

        add %ECX, 12
        add %EDX, 12
        add %ESI, 12

llvm-svn: 15090