Subzero: Remove IceString.

src/IceStringPool.h

Index: src/IceStringPool.h
diff --git a/src/IceStringPool.h b/src/IceStringPool.h
new file mode 100644
index 0000000000000000000000000000000000000000..e6b3d1117b10107fd276d048aad71f9580bf7d37
--- /dev/null
+++ b/src/IceStringPool.h
@@ -0,0 +1,174 @@
+//===- subzero/src/IceStringPool.h - String pooling -------------*- C++ -*-===//
+//
+//                        The Subzero Code Generator
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// \brief Defines unique pooled strings with short unique IDs.  This makes
+/// hashing, equality testing, and ordered comparison faster, and avoids a lot
+/// of memory allocation compared to directly using std::string.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef SUBZERO_SRC_ICESTRINGPOOL_H
+#define SUBZERO_SRC_ICESTRINGPOOL_H
+
+#include <cstdint> // uintptr_t
+#include <string>
+
+namespace Ice {
+
+class StringPool {
+  StringPool(const StringPool &) = delete;
+  StringPool &operator=(const StringPool &) = delete;
+
+public:
+  using IDType = uintptr_t;
+
+  StringPool() = default;
+  ~StringPool() = default;
+  IDType getNewID() {
+    // TODO(stichnot): Make it so that the GlobalString ctor doesn't have to
+    // grab the lock, and instead does an atomic increment of NextID.
+    auto NewID = NextID;
+    NextID += IDIncrement;
+    return NewID;
+  }
+  IDType getOrAddString(const std::string &Value) {
+    auto Iter = StringToId.find(Value);
+    if (Iter == StringToId.end()) {
+      auto *NewStr = new std::string(Value);
+      auto ID = reinterpret_cast<IDType>(NewStr);
+      StringToId[Value].reset(NewStr);
+      return ID;
+    }
+    return reinterpret_cast<IDType>(Iter->second.get());
+  }
+  void dump(Ostream &Str) const {
+    if (StringToId.empty())
+      return;
+    Str << "String pool (NumStrings=" << StringToId.size()
+        << " NumIDs=" << ((NextID - FirstID) / IDIncrement) << "):";
+    for (const auto &Tuple : StringToId) {
+      Str << " " << Tuple.first;
+    }
+    Str << "\n";
+  }
+
+private:
+  static constexpr IDType FirstID = 1;
+  static constexpr IDType IDIncrement = 2;
+  IDType NextID = FirstID;
+  std::unordered_map<std::string, std::unique_ptr<std::string>> StringToId;
+};
+
+template <typename Traits> class StringID {
+public:
+  using IDType = StringPool::IDType;
+
+  StringID() = default; // Create a default, invalid StringID.
+  StringID(const StringID &) = default;
+  StringID &operator=(const StringID &) = default;
+
+  /// Create a unique StringID without an actual string, by grabbing the next
+  /// unique integral ID from the Owner.
+  static StringID createWithoutString(const typename Traits::OwnerType *Owner) {
+    return StringID(Owner);
+  }
+  /// Create a unique StringID that holds an actual string, by fetching or
+  /// adding the string from the Owner's pool.
+  static StringID createWithString(const typename Traits::OwnerType *Owner,
+                                   const std::string &Value) {
+    return StringID(Owner, Value);
+  }
+
+  /// Tests whether the StringID was initialized with respect to an actual
+  /// std::string value, i.e. via StringID::createWithString().
+  bool hasStdString() const { return isValid() && ((ID & 0x1) == 0); }
+
+  IDType getID() const {
+    assert(isValid());
+    return ID;
+  }
+  const std::string &toString() const {
+    if (!hasStdString())
+      llvm::report_fatal_error(
+          "toString() called when hasStdString() is false");
+    return *reinterpret_cast<std::string *>(ID);
+  }
+  std::string toStringOrEmpty() const {
+    if (hasStdString())
+      return toString();
+    return "";
+  }
+
+  bool operator==(const StringID &Other) const { return ID == Other.ID; }
+  bool operator!=(const StringID &Other) const { return !(*this == Other); }
+  bool operator<(const StringID &Other) const {
+    const bool ThisHasString = hasStdString();
+    const bool OtherHasString = Other.hasStdString();
+    // Do a normal string comparison if both have strings.
+    if (ThisHasString && OtherHasString)
+      return this->toString() < Other.toString();
+    // Use the ID as a tiebreaker if neither has a string.
+    if (!ThisHasString && !OtherHasString)
+      return ID < Other.ID;
+    // If exactly one has a string, then that one comes first.
+    assert(!OtherHasString);
+    return ThisHasString;
+  }
+
+private:
+  static constexpr IDType InvalidID = 0;
+  IDType ID = InvalidID;
+
+  explicit StringID(const typename Traits::OwnerType *Owner)
+      : ID(Traits::getStrings(Owner)->getNewID()) {}
+  StringID(const typename Traits::OwnerType *Owner, const std::string &Value)
+      : ID(Traits::getStrings(Owner)->getOrAddString(Value)) {
+    assert(hasStdString());
+  }
+  bool isValid() const { return ID != InvalidID; }
+};
+
+// TODO(stichnot, jpp): Move GlobalStringPoolTraits definition into
+// IceGlobalContext.h, once the include order issues are solved.
+struct GlobalStringPoolTraits {
+  using OwnerType = GlobalContext;
+  static LockedPtr<StringPool> getStrings(const OwnerType *Owner);
+};
+
+using GlobalString = StringID<struct GlobalStringPoolTraits>;
+
+template <typename T>
+Ostream &operator<<(Ostream &Str, const StringID<T> &Name) {
+  return Str << Name.toString();
+}
+
+template <typename T>
+std::string operator+(const std::string &A, const StringID<T> &B) {
+  return A + B.toString();
+}
+
+template <typename T>
+std::string operator+(const StringID<T> &A, const std::string &B) {
+  return A.toString() + B;
+}
+
+} // end of namespace Ice
+
+namespace std {
+template <typename T> struct hash<Ice::StringID<T>> {
+  size_t operator()(const Ice::StringID<T> &Key) const {
+    if (Key.hasStdString())
+      return hash<std::string>()(Key.toString());
+    return hash<Ice::StringPool::IDType>()(Key.getID());
+  }
+};
+} // end of namespace std
+
+#endif // SUBZERO_SRC_ICESTRINGPOOL_H