text: //===- IntervalPartition.h - Interval partition Calculation -----*- C++ -*-===//
  //
  // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
  // See https://llvm.org/LICENSE.txt for license information.
  // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
  //
  //===----------------------------------------------------------------------===//
  //
  // This file contains the declaration of the IntervalPartition class, which
  // calculates and represents the interval partition of a function, or a
  // preexisting interval partition.
  //
  // In this way, the interval partition may be used to reduce a flow graph down
  // to its degenerate single node interval partition (unless it is irreducible).
  //
  // TODO: The IntervalPartition class should take a bool parameter that tells
  // whether it should add the "tails" of an interval to an interval itself or if
  // they should be represented as distinct intervals.
  //
  //===----------------------------------------------------------------------===//
  
  #ifndef LLVM_ANALYSIS_INTERVALPARTITION_H
  #define LLVM_ANALYSIS_INTERVALPARTITION_H
  
  #include "llvm/Pass.h"
  #include <map>
  #include <vector>
  
  namespace llvm {
  
  class BasicBlock;
  class Interval;
  
  //===----------------------------------------------------------------------===//
  //
  // IntervalPartition - This class builds and holds an "interval partition" for
  // a function.  This partition divides the control flow graph into a set of
  // maximal intervals, as defined with the properties above.  Intuitively, an
  // interval is a (possibly nonexistent) loop with a "tail" of non-looping
  // nodes following it.
  //
  class IntervalPartition : public FunctionPass {
    using IntervalMapTy = std::map<BasicBlock *, Interval *>;
    IntervalMapTy IntervalMap;
  
    using IntervalListTy = std::vector<Interval *>;
    Interval *RootInterval = nullptr;
    std::vector<Interval *> Intervals;
  
  public:
    static char ID; // Pass identification, replacement for typeid
  
    IntervalPartition();
  
    // run - Calculate the interval partition for this function
    bool runOnFunction(Function &F) override;
  
    // IntervalPartition ctor - Build a reduced interval partition from an
    // existing interval graph.  This takes an additional boolean parameter to
    // distinguish it from a copy constructor.  Always pass in false for now.
    IntervalPartition(IntervalPartition &I, bool);
  
    // print - Show contents in human readable format...
    void print(raw_ostream &O, const Module* = nullptr) const override;
  
    // getRootInterval() - Return the root interval that contains the starting
    // block of the function.
    inline Interval *getRootInterval() { return RootInterval; }
  
    // isDegeneratePartition() - Returns true if the interval partition contains
    // a single interval, and thus cannot be simplified anymore.
    bool isDegeneratePartition() { return Intervals.size() == 1; }
  
    // TODO: isIrreducible - look for triangle graph.
  
    // getBlockInterval - Return the interval that a basic block exists in.
    inline Interval *getBlockInterval(BasicBlock *BB) {
      IntervalMapTy::iterator I = IntervalMap.find(BB);
      return I != IntervalMap.end() ? I->second : nullptr;
    }
  
    // getAnalysisUsage - Implement the Pass API
    void getAnalysisUsage(AnalysisUsage &AU) const override {
      AU.setPreservesAll();
    }
  
    // Interface to Intervals vector...
    const std::vector<Interval*> &getIntervals() const { return Intervals; }
  
    // releaseMemory - Reset state back to before function was analyzed
    void releaseMemory() override;
  
  private:
    // addIntervalToPartition - Add an interval to the internal list of intervals,
    // and then add mappings from all of the basic blocks in the interval to the
    // interval itself (in the IntervalMap).
    void addIntervalToPartition(Interval *I);
  
    // updatePredecessors - Interval generation only sets the successor fields of
    // the interval data structures.  After interval generation is complete,
    // run through all of the intervals and propagate successor info as
    // predecessor info.
    void updatePredecessors(Interval *Int);
  };
  
  } // end namespace llvm
  
  #endif // LLVM_ANALYSIS_INTERVALPARTITION_H
  