Add a comment on PHINode::Create().

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@128540 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Instructions.h

@@ -1829,6 +1829,8 @@ class PHINode : public Instruction {
 protected:
   virtual PHINode *clone_impl() const;
 public:
+  /// Constructors - NumReservedValues is a hint for the number of incoming
+  /// edges that this phi node will have (use 0 if you really have no idea).
   static PHINode *Create(const Type *Ty, unsigned NumReservedValues,
                          const Twine &NameStr = "",
                          Instruction *InsertBefore = 0) {