[sil] Add a variant of SmallSetVector that uses SmallPtrSet internally instead of SmallDenseSet.

Author: gottesmm

include/swift/Basic/SmallPtrSetVector.h

@@ -0,0 +1,52 @@
+//===--- SmallPtrSetVector.h ----------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2021 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef SWIFT_BASIC_SMALLPTRSETVECTOR_H
+#define SWIFT_BASIC_SMALLPTRSETVECTOR_H
+
+#include "swift/Basic/LLVM.h"
+#include "llvm/ADT/SetVector.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallVector.h"
+
+namespace swift {
+
+/// A SetVector that performs no allocations if smaller than a certain
+/// size. Uses a SmallPtrSet/SmallVector internally.
+template <typename T, unsigned VectorSize, unsigned SetSize = VectorSize>
+class SmallPtrSetVector : public llvm::SetVector<T, SmallVector<T, VectorSize>,
+                                                 SmallPtrSet<T, SetSize>> {
+public:
+  SmallPtrSetVector() = default;
+
+  /// Initialize a SmallPtrSetVector with a range of elements
+  template <typename It> SmallPtrSetVector(It Start, It End) {
+    this->insert(Start, End);
+  }
+};
+
+} // namespace swift
+
+namespace std {
+
+/// Implement std::swap in terms of SmallSetVector swap.
+///
+/// This matches llvm's implementation for SmallSetVector.
+template <typename T, unsigned VectorSize, unsigned SetSize = VectorSize>
+inline void swap(swift::SmallPtrSetVector<T, VectorSize, SetSize> &LHS,
+                 swift::SmallPtrSetVector<T, VectorSize, SetSize> &RHS) {
+  LHS.swap(RHS);
+}
+
+} // end namespace std
+
+#endif