[llvm] [CAS] Add LLVMCAS library with InMemoryCAS implementation (PR #114096)

[Adrian Prantl via llvm-commits]

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+//===- InMemoryCAS.cpp ------------------------------------------*- 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "BuiltinCAS.h"
+#include "llvm/ADT/LazyAtomicPointer.h"
+#include "llvm/ADT/PointerIntPair.h"
+#include "llvm/ADT/TrieRawHashMap.h"
+#include "llvm/Support/Allocator.h"
+#include "llvm/Support/Casting.h"
+#include "llvm/Support/ThreadSafeAllocator.h"
+#include "llvm/Support/TrailingObjects.h"
+
+using namespace llvm;
+using namespace llvm::cas;
+using namespace llvm::cas::builtin;
+
+namespace {
+
+class InMemoryObject;
+
+/// Index of referenced IDs (map: Hash -> InMemoryObject*). Uses
+/// LazyAtomicPointer to coordinate creation of objects.
+using InMemoryIndexT =
+    ThreadSafeTrieRawHashMap<LazyAtomicPointer<const InMemoryObject>,
+                             sizeof(HashType)>;
+
+/// Values in \a InMemoryIndexT. \a InMemoryObject's point at this to access
+/// their hash.
+using InMemoryIndexValueT = InMemoryIndexT::value_type;
+
+class InMemoryObject {
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adrian-prantl wrote:

Doxyen comment?

https://github.com/llvm/llvm-project/pull/114096