[Legalizer] Use SmallSetVector instead of SetVector.

NFC

llvm-svn: 315758
diff --git a/llvm/lib/CodeGen/GlobalISel/Legalizer.cpp b/llvm/lib/CodeGen/GlobalISel/Legalizer.cpp
index a9847de..83e5dc4 100644
--- a/llvm/lib/CodeGen/GlobalISel/Legalizer.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/Legalizer.cpp
@@ -70,7 +70,7 @@
   // convergence for performance reasons.
   bool Changed = false;
   MachineBasicBlock::iterator NextMI;
-  using VecType = SetVector<MachineInstr *, SmallVector<MachineInstr *, 8>>;
+  using VecType = SmallSetVector<MachineInstr *, 8>;
   VecType WorkList;
   VecType CombineList;
   for (auto &MBB : MF) {