1//===- PredIteratorCache.h - pred_iterator Cache ----------------*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file defines the PredIteratorCache class.
10//
11//===----------------------------------------------------------------------===//
12
13#ifndef LLVM_IR_PREDITERATORCACHE_H
14#define LLVM_IR_PREDITERATORCACHE_H
15
16#include "llvm/ADT/ArrayRef.h"
17#include "llvm/ADT/DenseMap.h"
18#include "llvm/ADT/SmallVector.h"
19#include "llvm/IR/CFG.h"
20#include "llvm/Support/Allocator.h"
21
22namespace llvm {
23
24/// PredIteratorCache - This class is an extremely trivial cache for
25/// predecessor iterator queries.  This is useful for code that repeatedly
26/// wants the predecessor list for the same blocks.
27class PredIteratorCache {
28  /// BlockToPredsMap - Pointer to null-terminated list.
29  mutable DenseMap<BasicBlock *, BasicBlock **> BlockToPredsMap;
30  mutable DenseMap<BasicBlock *, unsigned> BlockToPredCountMap;
31
32  /// Memory - This is the space that holds cached preds.
33  BumpPtrAllocator Memory;
34
35private:
36  /// GetPreds - Get a cached list for the null-terminated predecessor list of
37  /// the specified block.  This can be used in a loop like this:
38  ///   for (BasicBlock **PI = PredCache->GetPreds(BB); *PI; ++PI)
39  ///      use(*PI);
40  /// instead of:
41  /// for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
42  BasicBlock **GetPreds(BasicBlock *BB) {
43    BasicBlock **&Entry = BlockToPredsMap[BB];
44    if (Entry)
45      return Entry;
46
47    SmallVector<BasicBlock *, 32> PredCache(predecessors(BB));
48    PredCache.push_back(nullptr); // null terminator.
49
50    BlockToPredCountMap[BB] = PredCache.size() - 1;
51
52    Entry = Memory.Allocate<BasicBlock *>(PredCache.size());
53    std::copy(PredCache.begin(), PredCache.end(), Entry);
54    return Entry;
55  }
56
57  unsigned GetNumPreds(BasicBlock *BB) const {
58    auto Result = BlockToPredCountMap.find(BB);
59    if (Result != BlockToPredCountMap.end())
60      return Result->second;
61    return BlockToPredCountMap[BB] = pred_size(BB);
62  }
63
64public:
65  size_t size(BasicBlock *BB) const { return GetNumPreds(BB); }
66  ArrayRef<BasicBlock *> get(BasicBlock *BB) {
67    return ArrayRef(GetPreds(BB), GetNumPreds(BB));
68  }
69
70  /// clear - Remove all information.
71  void clear() {
72    BlockToPredsMap.clear();
73    BlockToPredCountMap.clear();
74    Memory.Reset();
75  }
76};
77
78} // end namespace llvm
79
80#endif
81