read a few instructions, fix some bugs. This is enough to be able to round

trip function bodies like this:

define <2 x i64> @foo(<2 x i64> %x, <2 x i64> %y) {
        %tmp4 = bitcast <2 x i64> %y to <8 x i16>               ; <<8 x i16>> [#uses=1]
        %tmp5 = bitcast <2 x i64> %x to <8 x i16>               ; <<8 x i16>> [#uses=1]
        %tmp = add <8 x i16> %tmp5, %tmp4               ; <<8 x i16>> [#uses=1]
        %tmp6 = bitcast <8 x i16> %tmp to <2 x i64>             ; <<2 x i64>> [#uses=1]
        ret <2 x i64> %tmp6
}

llvm-svn: 36640