Implement sse4.2 string/text processing instructions:

Implement sse4.2 string/text processing instructions:
Add patterns and instruction encoding information.
Add custom lowering to deal with hardwired return register of
uncertain type (xmm0).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@79377 91177308-0d34-0410-b5e6-96231b3b80d8