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1 //===- llvm/Support/PredIteratorCache.h - pred_iterator Cache ---*- C++ -*-===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file defines the PredIteratorCache class.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "llvm/Support/Allocator.h"
15 #include "llvm/Support/CFG.h"
16 #include "llvm/ADT/DenseMap.h"
17 #include "llvm/ADT/SmallVector.h"
18 
19 #ifndef LLVM_SUPPORT_PREDITERATORCACHE_H
20 #define LLVM_SUPPORT_PREDITERATORCACHE_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     DenseMap<BasicBlock*, BasicBlock**> BlockToPredsMap;
30     DenseMap<BasicBlock*, unsigned> BlockToPredCountMap;
31 
32     /// Memory - This is the space that holds cached preds.
33     BumpPtrAllocator Memory;
34   public:
35 
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) return Entry;
45 
46       SmallVector<BasicBlock*, 32> PredCache(pred_begin(BB), pred_end(BB));
47       PredCache.push_back(0); // null terminator.
48 
49       BlockToPredCountMap[BB] = PredCache.size()-1;
50 
51       Entry = Memory.Allocate<BasicBlock*>(PredCache.size());
52       std::copy(PredCache.begin(), PredCache.end(), Entry);
53       return Entry;
54     }
55 
GetNumPreds(BasicBlock * BB)56     unsigned GetNumPreds(BasicBlock *BB) {
57       GetPreds(BB);
58       return BlockToPredCountMap[BB];
59     }
60 
61     /// clear - Remove all information.
clear()62     void clear() {
63       BlockToPredsMap.clear();
64       BlockToPredCountMap.clear();
65       Memory.Reset();
66     }
67   };
68 } // end namespace llvm
69 
70 #endif
71