[X86] Use SHLD with both inputs from the same register to implement rotate on...

[X86] Use SHLD with both inputs from the same register to implement rotate on Sandy Bridge and later Intel CPUs

Summary:
Sandy Bridge and later CPUs have better throughput using a SHLD to implement rotate versus the normal rotate instructions. Additionally it saves one uop and avoids a partial flag update dependency.

This patch implements this change on any Sandy Bridge or later processor without BMI2 instructions. With BMI2 we will use RORX as we currently do.

Reviewers: zvi

Reviewed By: zvi

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D30181

llvm-svn: 295697