[llvm] [ADT] Add TrieRawHashMap (PR #69528)

[Aman LaChapelle via llvm-commits]

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@@ -0,0 +1,483 @@
+//===- TrieRawHashMap.cpp -------------------------------------------------===//
+//
+// 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 "llvm/ADT/TrieRawHashMap.h"
+#include "TrieHashIndexGenerator.h"
+#include "llvm/ADT/LazyAtomicPointer.h"
+#include "llvm/ADT/StringExtras.h"
+#include "llvm/Support/Allocator.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/ThreadSafeAllocator.h"
+#include "llvm/Support/raw_ostream.h"
+#include <memory>
+
+using namespace llvm;
+
+namespace {
+struct TrieNode {
+  const bool IsSubtrie = false;
+
+  TrieNode(bool IsSubtrie) : IsSubtrie(IsSubtrie) {}
+
+  static void *operator new(size_t Size) { return ::malloc(Size); }
+  void operator delete(void *Ptr) { ::free(Ptr); }
+};
+
+struct TrieContent final : public TrieNode {
+  const uint8_t ContentOffset;
+  const uint8_t HashSize;
+  const uint8_t HashOffset;
+
+  void *getValuePointer() const {
+    auto *Content = reinterpret_cast<const uint8_t *>(this) + ContentOffset;
+    return const_cast<uint8_t *>(Content);
+  }
+
+  ArrayRef<uint8_t> getHash() const {
+    auto *Begin = reinterpret_cast<const uint8_t *>(this) + HashOffset;
+    return ArrayRef(Begin, Begin + HashSize);
+  }
+
+  TrieContent(size_t ContentOffset, size_t HashSize, size_t HashOffset)
+      : TrieNode(/*IsSubtrie=*/false), ContentOffset(ContentOffset),
+        HashSize(HashSize), HashOffset(HashOffset) {}
+
+  static bool classof(const TrieNode *TN) { return !TN->IsSubtrie; }
+};
+
+static_assert(sizeof(TrieContent) ==
+                  ThreadSafeTrieRawHashMapBase::TrieContentBaseSize,
+              "Check header assumption!");
+
+class TrieSubtrie final : public TrieNode {
+public:
+  TrieNode *get(size_t I) const { return Slots[I].load(); }
+
+  TrieSubtrie *
+  sink(size_t I, TrieContent &Content, size_t NumSubtrieBits, size_t NewI,
+       function_ref<TrieSubtrie *(std::unique_ptr<TrieSubtrie>)> Saver);
+
+  static std::unique_ptr<TrieSubtrie> create(size_t StartBit, size_t NumBits);
+
+  explicit TrieSubtrie(size_t StartBit, size_t NumBits);
+
+  static bool classof(const TrieNode *TN) { return TN->IsSubtrie; }
+
+private:
+  // FIXME: Use a bitset to speed up access:
+  //
+  //     std::array<std::atomic<uint64_t>, NumSlots/64> IsSet;
+  //
+  // This will avoid needing to visit sparsely filled slots in
+  // \a ThreadSafeTrieRawHashMapBase::destroyImpl() when there's a non-trivial
+  // destructor.
+  //
+  // It would also greatly speed up iteration, if we add that some day, and
+  // allow get() to return one level sooner.
+  //
+  // This would be the algorithm for updating IsSet (after updating Slots):
+  //
+  //     std::atomic<uint64_t> &Bits = IsSet[I.High];
+  //     const uint64_t NewBit = 1ULL << I.Low;
+  //     uint64_t Old = 0;
+  //     while (!Bits.compare_exchange_weak(Old, Old | NewBit))
+  //       ;
+
+  // For debugging.
+  unsigned StartBit = 0;
+  unsigned NumBits = 0;
+  friend class llvm::ThreadSafeTrieRawHashMapBase;
+
+public:
+  /// Linked list for ownership of tries. The pointer is owned by TrieSubtrie.
+  std::atomic<TrieSubtrie *> Next;
+
+  /// The (co-allocated) slots of the subtrie.
+  MutableArrayRef<LazyAtomicPointer<TrieNode>> Slots;
+};
+} // end namespace
+
+static size_t getTrieTailSize(size_t StartBit, size_t NumBits) {
+  assert(NumBits < 20 && "Tries should have fewer than ~1M slots");
+  return sizeof(TrieNode *) * (1u << NumBits);
+}
+
+std::unique_ptr<TrieSubtrie> TrieSubtrie::create(size_t StartBit,
+                                                 size_t NumBits) {
+  size_t Size = sizeof(TrieSubtrie) + getTrieTailSize(StartBit, NumBits);
+  void *Memory = ::malloc(Size);
+  TrieSubtrie *S = ::new (Memory) TrieSubtrie(StartBit, NumBits);
----------------
bzcheeseman wrote:

Actually, is https://llvm.org/doxygen/classllvm_1_1TrailingObjects.html something that might be useful here? It looks like that's what you're going for, and this might be a little cleaner?

https://github.com/llvm/llvm-project/pull/69528