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

[Paul Kirth via llvm-commits]

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@@ -0,0 +1,320 @@
+//===- 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"
+
+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 {
+public:
+  enum class Kind {
+    /// Node with refs and data.
+    RefNode,
+
+    /// Node with refs and data co-allocated.
+    InlineNode,
+
+    Max = InlineNode,
+  };
+
+  Kind getKind() const { return IndexAndKind.getInt(); }
+  const InMemoryIndexValueT &getIndex() const {
+    assert(IndexAndKind.getPointer());
+    return *IndexAndKind.getPointer();
+  }
+
+  ArrayRef<uint8_t> getHash() const { return getIndex().Hash; }
+
+  InMemoryObject() = delete;
+  InMemoryObject(InMemoryObject &&) = delete;
+  InMemoryObject(const InMemoryObject &) = delete;
+
+protected:
+  InMemoryObject(Kind K, const InMemoryIndexValueT &I) : IndexAndKind(&I, K) {}
+
+private:
+  enum Counts : int {
+    NumKindBits = 2,
+  };
+  PointerIntPair<const InMemoryIndexValueT *, NumKindBits, Kind> IndexAndKind;
+  static_assert((1U << NumKindBits) <= alignof(InMemoryIndexValueT),
+                "Kind will clobber pointer");
+  static_assert(((int)Kind::Max >> NumKindBits) == 0, "Kind will be truncated");
+
+public:
+  inline ArrayRef<char> getData() const;
+
+  inline ArrayRef<const InMemoryObject *> getRefs() const;
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ilovepi wrote:

Why mark this (and other APIs) inline? 

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