Rename WeakVH to WeakTrackingVH; NFC

This relands r301424.

llvm-svn: 301812
diff --git a/llvm/lib/Transforms/Scalar/Reassociate.cpp b/llvm/lib/Transforms/Scalar/Reassociate.cpp
index 3dcab60..ef29d41 100644
--- a/llvm/lib/Transforms/Scalar/Reassociate.cpp
+++ b/llvm/lib/Transforms/Scalar/Reassociate.cpp
@@ -982,7 +982,7 @@
 /// Emit a tree of add instructions, summing Ops together
 /// and returning the result.  Insert the tree before I.
 static Value *EmitAddTreeOfValues(Instruction *I,
-                                  SmallVectorImpl<WeakVH> &Ops){
+                                  SmallVectorImpl<WeakTrackingVH> &Ops) {
   if (Ops.size() == 1) return Ops.back();
 
   Value *V1 = Ops.back();
@@ -1559,7 +1559,7 @@
             ? BinaryOperator::CreateAdd(MaxOccVal, MaxOccVal)
             : BinaryOperator::CreateFAdd(MaxOccVal, MaxOccVal);
 
-    SmallVector<WeakVH, 4> NewMulOps;
+    SmallVector<WeakTrackingVH, 4> NewMulOps;
     for (unsigned i = 0; i != Ops.size(); ++i) {
       // Only try to remove factors from expressions we're allowed to.
       BinaryOperator *BOp =