[PATCH] fix PR15296

[Nadav Rotem]

Patch #1:

+SDValue X86TargetLowering::LowerShift(SDValue Op, SelectionDAG &DAG) const {
+
+  EVT VT = Op.getValueType();

No need for extra space. 

Patch #2: 

Please write a few cost-model tests to make sure that we get the costs of the shifts right. 

Patch #3:

In this patch you are doing two things. 1. Move code from x86combine to x86lower, and add a new optimization. Please split this into two patches.

Thanks,
Nadav