[llvm] [CAS] Add OnDiskGraphDB and OnDiskKeyValueDB (PR #114102)

[Steven Wu via llvm-commits]

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@@ -0,0 +1,470 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+/// \file
+/// This declares OnDiskGraphDB, an ondisk CAS database with a fixed length
+/// hash. This is the class that implements the database storage scheme without
+/// exposing the hashing algorithm.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CAS_ONDISKGRAPHDB_H
+#define LLVM_CAS_ONDISKGRAPHDB_H
+
+#include "llvm/ADT/PointerUnion.h"
+#include "llvm/CAS/OnDiskDataAllocator.h"
+#include "llvm/CAS/OnDiskTrieRawHashMap.h"
+
+namespace llvm::cas::ondisk {
+
+/// Standard 8B reference inside OnDiskGraphDB.
+class InternalRef {
+public:
+  FileOffset getFileOffset() const { return FileOffset(Data); }
+  uint64_t getRawData() const { return Data; }
+
+  static InternalRef getFromRawData(uint64_t Data) { return InternalRef(Data); }
+  static InternalRef getFromOffset(FileOffset Offset) {
+    return InternalRef(Offset.get());
+  }
+
+  friend bool operator==(InternalRef LHS, InternalRef RHS) {
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cachemeifyoucan wrote:

This is c++20? I don't think we are there yet. 

https://github.com/llvm/llvm-project/pull/114102