[SLP] remove unnecessary state in matching reductions

This is NFC-intended. I'm still trying to figure out
how the loop where this is used works. It does not
seem like we require this data at all, but it's
hard to confirm given the complicated predicates.

Author: rotateright

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

@@ -6679,9 +6679,6 @@ class HorizontalReduction {
   /// The operation data of the reduction operation.
   OperationData RdxTreeInst;
 
-  /// The operation data for the leaf values that we perform a reduction on.
-  OperationData RdxLeafVal;
-
   /// Checks if the ParentStackElem.first should be marked as a reduction
   /// operation with an extra argument or as extra argument itself.
   void markExtraArg(std::pair<Instruction *, unsigned> &ParentStackElem,
@@ -6825,9 +6822,11 @@ class HorizontalReduction {
     if (!isValidElementType(Ty) || Ty->isPointerTy())
       return false;
 
-    RdxLeafVal.clear();
     ReductionRoot = B;
 
+    // The operation data for the leaf values that we perform a reduction on.
+    OperationData RdxLeafVal;
+
     // Post order traverse the reduction tree starting at B. We only handle true
     // trees containing only binary operators.
     SmallVector<std::pair<Instruction *, unsigned>, 32> Stack;