Reviewers for DAG changes

Hi all,

I have a patch which implements a new intrinsic
(https://reviews.llvm.org/D52286) and wanted to see if there would be
anyone willing to review it. In particular, someone who is familiar
with the DAG.

This patch implements a signed saturation intrinsic, which takes a
signed integer and saturates it to a specified number of bits. This is
a part of a previous thread which discusses adding intrinsics for
fixed point types:

Original thread:
http://lists.llvm.org/pipermail/llvm-dev/2018-August/125433.html

Specific intrinsics:
http://lists.llvm.org/pipermail/llvm-dev/2018-September/126311.html

The intrinsic gets expanded in the DAG and we would like to get
opinions/reviews from someone who has worked on the DAG before. Any
other comments and feedback are also welcome.

Thanks,
Leonard