[ADT][NFC] Simplify SmallSet (#109412)

- Remove dependence on `STLExtras.h`.
- Remove unused header inclusions.
- Make `count` use `contains` for deduplication.
- Replace hand-written linear scans on Vector by `std::find`.

Author: vhscampos

clang/lib/Basic/TargetID.cpp

@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "clang/Basic/TargetID.h"
+#include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallSet.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/TargetParser/TargetParser.h"

llvm/include/llvm/ADT/SmallSet.h

@@ -16,14 +16,10 @@
 
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/SmallVector.h"
-#include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/iterator.h"
-#include "llvm/Support/Compiler.h"
-#include "llvm/Support/type_traits.h"
 #include <cstddef>
 #include <functional>
 #include <set>
-#include <type_traits>
 #include <utility>
 
 namespace llvm {
@@ -139,10 +135,6 @@ 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 +155,7 @@ 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 +167,7 @@ class SmallSet {
       return std::make_pair(const_iterator(I), Inserted);
     }
 
-    VIterator I = vfind(V);
+    auto I = std::find(Vector.begin(), Vector.end(), 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 +192,11 @@ 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 I = std::find(Vector.begin(), Vector.end(), V);
+    if (I != Vector.end()) {
+      Vector.erase(I);
+      return true;
+    }
     return false;
   }
 
@@ -234,19 +220,12 @@ class SmallSet {
   /// Check if the SmallSet contains the given element.
   bool contains(const T &V) const {
     if (isSmall())
-      return vfind(V) != Vector.end();
+      return std::find(Vector.begin(), Vector.end(), V) != Vector.end();
     return Set.find(V) != Set.end();
   }
 
 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