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 
22 namespace 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.
27 class 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 
35 private:
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)
GetPreds(BasicBlock * BB)42   BasicBlock **GetPreds(BasicBlock *BB) {
43     BasicBlock **&Entry = BlockToPredsMap[BB];
44     if (Entry)
45       return Entry;
46 
47     SmallVector<BasicBlock *, 32> PredCache(pred_begin(BB), pred_end(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 
GetNumPreds(BasicBlock * BB)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] = std::distance(pred_begin(BB), pred_end(BB));
62   }
63 
64 public:
size(BasicBlock * BB)65   size_t size(BasicBlock *BB) const { return GetNumPreds(BB); }
get(BasicBlock * BB)66   ArrayRef<BasicBlock *> get(BasicBlock *BB) {
67     return makeArrayRef(GetPreds(BB), GetNumPreds(BB));
68   }
69 
70   /// clear - Remove all information.
clear()71   void clear() {
72     BlockToPredsMap.clear();
73     BlockToPredCountMap.clear();
74     Memory.Reset();
75   }
76 };
77 
78 } // end namespace llvm
79 
80 #endif
81