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

[David Blaikie via llvm-commits]

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@@ -0,0 +1,89 @@
+//===- TrieHashIndexGenerator.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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIB_SUPPORT_TRIEHASHINDEXGENERATOR_H
+#define LLVM_LIB_SUPPORT_TRIEHASHINDEXGENERATOR_H
+
+#include "llvm/ADT/ArrayRef.h"
+#include <optional>
+
+namespace llvm {
+
+struct IndexGenerator {
+  size_t NumRootBits;
+  size_t NumSubtrieBits;
+  ArrayRef<uint8_t> Bytes;
+  std::optional<size_t> StartBit = std::nullopt;
+
+  size_t getNumBits() const {
+    assert(StartBit);
+    size_t TotalNumBits = Bytes.size() * 8;
+    assert(*StartBit <= TotalNumBits);
+    return std::min(*StartBit ? NumSubtrieBits : NumRootBits,
+                    TotalNumBits - *StartBit);
+  }
+  size_t next() {
+    size_t Index;
+    if (!StartBit) {
+      StartBit = 0;
+      Index = getIndex(Bytes, *StartBit, NumRootBits);
+    } else {
+      *StartBit += *StartBit ? NumSubtrieBits : NumRootBits;
+      assert((*StartBit - NumRootBits) % NumSubtrieBits == 0);
+      Index = getIndex(Bytes, *StartBit, NumSubtrieBits);
+    }
+    return Index;
+  }
+
+  size_t hint(unsigned Index, unsigned Bit) {
+    assert(Index >= 0);
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dwblaikie wrote:

This is tautological, since `Index` is unsigned. (I'm surprised this didn't produce a warning?)

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