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       1             : //===- 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             : #ifndef LLVM_IR_PREDITERATORCACHE_H
      15             : #define LLVM_IR_PREDITERATORCACHE_H
      16             : 
      17             : #include "llvm/ADT/ArrayRef.h"
      18             : #include "llvm/ADT/DenseMap.h"
      19             : #include "llvm/ADT/SmallVector.h"
      20             : #include "llvm/IR/CFG.h"
      21             : #include "llvm/Support/Allocator.h"
      22             : 
      23             : namespace llvm {
      24             : 
      25             : /// PredIteratorCache - This class is an extremely trivial cache for
      26             : /// predecessor iterator queries.  This is useful for code that repeatedly
      27             : /// wants the predecessor list for the same blocks.
      28             : class PredIteratorCache {
      29             :   /// BlockToPredsMap - Pointer to null-terminated list.
      30             :   mutable DenseMap<BasicBlock *, BasicBlock **> BlockToPredsMap;
      31             :   mutable DenseMap<BasicBlock *, unsigned> BlockToPredCountMap;
      32             : 
      33             :   /// Memory - This is the space that holds cached preds.
      34             :   BumpPtrAllocator Memory;
      35             : 
      36             : private:
      37             :   /// GetPreds - Get a cached list for the null-terminated predecessor list of
      38             :   /// the specified block.  This can be used in a loop like this:
      39             :   ///   for (BasicBlock **PI = PredCache->GetPreds(BB); *PI; ++PI)
      40             :   ///      use(*PI);
      41             :   /// instead of:
      42             :   /// for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
      43     4260105 :   BasicBlock **GetPreds(BasicBlock *BB) {
      44     4260105 :     BasicBlock **&Entry = BlockToPredsMap[BB];
      45     4260105 :     if (Entry)
      46             :       return Entry;
      47             : 
      48      244330 :     SmallVector<BasicBlock *, 32> PredCache(pred_begin(BB), pred_end(BB));
      49      244330 :     PredCache.push_back(nullptr); // null terminator.
      50             : 
      51      244330 :     BlockToPredCountMap[BB] = PredCache.size() - 1;
      52             : 
      53      488660 :     Entry = Memory.Allocate<BasicBlock *>(PredCache.size());
      54             :     std::copy(PredCache.begin(), PredCache.end(), Entry);
      55      244330 :     return Entry;
      56             :   }
      57             : 
      58     4342828 :   unsigned GetNumPreds(BasicBlock *BB) const {
      59     4342828 :     auto Result = BlockToPredCountMap.find(BB);
      60     4342828 :     if (Result != BlockToPredCountMap.end())
      61     4098498 :       return Result->second;
      62      488660 :     return BlockToPredCountMap[BB] = std::distance(pred_begin(BB), pred_end(BB));
      63             :   }
      64             : 
      65             : public:
      66       81948 :   size_t size(BasicBlock *BB) const { return GetNumPreds(BB); }
      67     4260105 :   ArrayRef<BasicBlock *> get(BasicBlock *BB) {
      68     4260105 :     return makeArrayRef(GetPreds(BB), GetNumPreds(BB));
      69             :   }
      70             : 
      71             :   /// clear - Remove all information.
      72        1548 :   void clear() {
      73        1548 :     BlockToPredsMap.clear();
      74        1548 :     BlockToPredCountMap.clear();
      75        1548 :     Memory.Reset();
      76        1548 :   }
      77             : };
      78             : 
      79             : } // end namespace llvm
      80             : 
      81             : #endif