include/llvm/IR/PredIteratorCache.h

   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)
  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
  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:
  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