[clang] [clang][ssaf] Add EntityId and EntityIdTable for efficient entity handling (PR #171660)

[Jan Korous via cfe-commits]

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@@ -0,0 +1,49 @@
+//===- EntityId.h -----------------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines the EntityId class, which provides a lightweight opaque
+// handle to entities in an EntityIdTable. EntityIds are index-based for
+// efficient comparison and lookup.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_ANALYSIS_SCALABLE_MODEL_ENTITY_ID_H
+#define LLVM_CLANG_ANALYSIS_SCALABLE_MODEL_ENTITY_ID_H
+
+#include <cstddef>
+
+namespace clang {
+namespace ssaf {
+
+class EntityIdTable;
+
+/// Lightweight opaque handle representing an entity in an EntityIdTable.
+///
+/// EntityIds are created by EntityIdTable. Equality and ordering comparisons
+/// are well-defined for EntityIds created by the same EntityIdTable.
+///
+/// \see EntityIdTable
+class EntityId {
+  friend class EntityIdTable;
+
+  size_t Index;
+
+  explicit EntityId(size_t Index) : Index(Index) {}
+
+  EntityId() = delete;
+
+public:
+  bool operator==(const EntityId &Other) const { return Index == Other.Index; }
+  bool operator<(const EntityId &Other) const { return Index < Other.Index; }
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jkorous-apple wrote:

It's the latter. EntityId will very likely be used as an element type in `std::set` or `std::map` in the summary data.

https://github.com/llvm/llvm-project/pull/171660