Use SmallVectorImpl& instead of SmallVector to avoid repeating small vector size.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@186274 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/RegAllocFast.cpp b/lib/CodeGen/RegAllocFast.cpp
index 58d00da..6617e50 100644
--- a/lib/CodeGen/RegAllocFast.cpp
+++ b/lib/CodeGen/RegAllocFast.cpp
@@ -293,7 +293,7 @@
     // If this register is used by DBG_VALUE then insert new DBG_VALUE to
     // identify spilled location as the place to find corresponding variable's
     // value.
-    SmallVector<MachineInstr *, 4> &LRIDbgValues =
+    SmallVectorImpl<MachineInstr *> &LRIDbgValues =
       LiveDbgValueMap[LRI->VirtReg];
     for (unsigned li = 0, le = LRIDbgValues.size(); li != le; ++li) {
       MachineInstr *DBG = LRIDbgValues[li];