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 makeArrayRef(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