[PATCH] [X86] Tune LEA usage for Silvermont

[Nadav Rotem]

+  bool isSafeToClobberEFLAGS(MachineBasicBlock &MBB,
+                             MachineBasicBlock::iterator I) const;
+

Please document this function.  Everything else LGTM.

http://reviews.llvm.org/D3826