[ADT] Use range-based helper functions in SmallSet

Replace code that relies on iterators by LLVM helper functions that take
ranges. This makes the code simpler and more readable.

Author: vhscampos

llvm/include/llvm/ADT/SmallSet.h

@@ -139,10 +139,6 @@ class SmallSet {
   SmallVector<T, N> Vector;
   std::set<T, C> Set;
 
-  using VIterator = typename SmallVector<T, N>::const_iterator;
-  using SIterator = typename std::set<T, C>::const_iterator;
-  using mutable_iterator = typename SmallVector<T, N>::iterator;
-
   // In small mode SmallPtrSet uses linear search for the elements, so it is
   // not a good idea to choose this value too high. You may consider using a
   // DenseSet<> instead if you expect many elements in the set.
@@ -163,13 +159,7 @@ class SmallSet {
   }
 
   /// count - Return 1 if the element is in the set, 0 otherwise.
-  size_type count(const T &V) const {
-    if (isSmall()) {
-      // Since the collection is small, just do a linear search.
-      return vfind(V) == Vector.end() ? 0 : 1;
-    }
-    return Set.count(V);
-  }
+  size_type count(const T &V) const { return contains(V) ? 1 : 0; }
 
   /// insert - Insert an element into the set if it isn't already there.
   /// Returns a pair. The first value of it is an iterator to the inserted
@@ -181,7 +171,7 @@ class SmallSet {
       return std::make_pair(const_iterator(I), Inserted);
     }
 
-    VIterator I = vfind(V);
+    auto I = llvm::find(Vector, V);
     if (I != Vector.end())    // Don't reinsert if it already exists.
       return std::make_pair(const_iterator(I), false);
     if (Vector.size() < N) {
@@ -206,11 +196,12 @@ class SmallSet {
   bool erase(const T &V) {
     if (!isSmall())
       return Set.erase(V);
-    for (mutable_iterator I = Vector.begin(), E = Vector.end(); I != E; ++I)
-      if (*I == V) {
-        Vector.erase(I);
-        return true;
-      }
+
+    auto It = llvm::find(Vector, V);
+    if (It != Vector.end()) {
+      Vector.erase(It);
+      return true;
+    }
     return false;
   }
 
@@ -234,19 +225,12 @@ class SmallSet {
   /// Check if the SmallSet contains the given element.
   bool contains(const T &V) const {
     if (isSmall())
-      return vfind(V) != Vector.end();
-    return Set.find(V) != Set.end();
+      return llvm::is_contained(Vector, V);
+    return llvm::is_contained(Set, V);
   }
 
 private:
   bool isSmall() const { return Set.empty(); }
-
-  VIterator vfind(const T &V) const {
-    for (VIterator I = Vector.begin(), E = Vector.end(); I != E; ++I)
-      if (*I == V)
-        return I;
-    return Vector.end();
-  }
 };
 
 /// If this set is of pointer values, transparently switch over to using