From 062470ef689aadbaddd254546f4d84171ce1b190 Mon Sep 17 00:00:00 2001
From: Peter Johnson <johnson.peter@gmail.com>
Date: Mon, 15 Aug 2016 22:05:47 -0700
Subject: [PATCH] Add llvm::SmallSet. (#90)

---
 include/llvm/SmallSet.h | 136 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 136 insertions(+)
 create mode 100644 include/llvm/SmallSet.h

diff --git a/include/llvm/SmallSet.h b/include/llvm/SmallSet.h
new file mode 100644
index 0000000000..3dfd1f9bd9
--- /dev/null
+++ b/include/llvm/SmallSet.h
@@ -0,0 +1,136 @@
+//===- llvm/ADT/SmallSet.h - 'Normally small' sets --------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines the SmallSet class.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ADT_SMALLSET_H
+#define LLVM_ADT_SMALLSET_H
+
+#include "llvm/None.h"
+#include "llvm/SmallPtrSet.h"
+#include "llvm/SmallVector.h"
+#include <set>
+
+namespace llvm {
+
+/// SmallSet - This maintains a set of unique values, optimizing for the case
+/// when the set is small (less than N).  In this case, the set can be
+/// maintained with no mallocs.  If the set gets large, we expand to using an
+/// std::set to maintain reasonable lookup times.
+///
+/// Note that this set does not provide a way to iterate over members in the
+/// set.
+template <typename T, unsigned N,  typename C = std::less<T> >
+class SmallSet {
+  /// Use a SmallVector to hold the elements here (even though it will never
+  /// reach its 'large' stage) to avoid calling the default ctors of elements
+  /// we will never use.
+  SmallVector<T, N> Vector;
+  std::set<T, C> Set;
+  typedef typename SmallVector<T, N>::const_iterator VIterator;
+  typedef typename SmallVector<T, N>::iterator mutable_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.
+  static_assert(N <= 32, "N should be small");
+
+public:
+  typedef size_t size_type;
+  SmallSet() {}
+
+  bool LLVM_ATTRIBUTE_UNUSED_RESULT empty() const {
+    return Vector.empty() && Set.empty();
+  }
+
+  size_type size() const {
+    return isSmall() ? Vector.size() : Set.size();
+  }
+
+  /// 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;
+    } else {
+      return Set.count(V);
+    }
+  }
+
+  /// insert - Insert an element into the set if it isn't already there.
+  /// Returns true if the element is inserted (it was not in the set before).
+  /// The first value of the returned pair is unused and provided for
+  /// partial compatibility with the standard library self-associative container
+  /// concept.
+  // FIXME: Add iterators that abstract over the small and large form, and then
+  // return those here.
+  std::pair<NoneType, bool> insert(const T &V) {
+    if (!isSmall())
+      return std::make_pair(None, Set.insert(V).second);
+
+    VIterator I = vfind(V);
+    if (I != Vector.end())    // Don't reinsert if it already exists.
+      return std::make_pair(None, false);
+    if (Vector.size() < N) {
+      Vector.push_back(V);
+      return std::make_pair(None, true);
+    }
+
+    // Otherwise, grow from vector to set.
+    while (!Vector.empty()) {
+      Set.insert(Vector.back());
+      Vector.pop_back();
+    }
+    Set.insert(V);
+    return std::make_pair(None, true);
+  }
+
+  template <typename IterT>
+  void insert(IterT I, IterT E) {
+    for (; I != E; ++I)
+      insert(*I);
+  }
+
+  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;
+      }
+    return false;
+  }
+
+  void clear() {
+    Vector.clear();
+    Set.clear();
+  }
+
+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
+/// SmallPtrSet for performance.
+template <typename PointeeType, unsigned N>
+class SmallSet<PointeeType*, N> : public SmallPtrSet<PointeeType*, N> {};
+
+} // end namespace llvm
+
+#endif