1 //===- IntervalPartition.h - Interval partition Calculation -----*- 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 contains the declaration of the IntervalPartition class, which
11 // calculates and represents the interval partition of a function, or a
12 // preexisting interval partition.
13 //
14 // In this way, the interval partition may be used to reduce a flow graph down
15 // to its degenerate single node interval partition (unless it is irreducible).
16 //
17 // TODO: The IntervalPartition class should take a bool parameter that tells
18 // whether it should add the "tails" of an interval to an interval itself or if
19 // they should be represented as distinct intervals.
20 //
21 //===----------------------------------------------------------------------===//
22 
23 #ifndef LLVM_ANALYSIS_INTERVALPARTITION_H
24 #define LLVM_ANALYSIS_INTERVALPARTITION_H
25 
26 #include "llvm/Pass.h"
27 #include <map>
28 #include <vector>
29 
30 namespace llvm {
31 
32 class BasicBlock;
33 class Interval;
34 
35 //===----------------------------------------------------------------------===//
36 //
37 // IntervalPartition - This class builds and holds an "interval partition" for
38 // a function.  This partition divides the control flow graph into a set of
39 // maximal intervals, as defined with the properties above.  Intuitively, an
40 // interval is a (possibly nonexistent) loop with a "tail" of non-looping
41 // nodes following it.
42 //
43 class IntervalPartition : public FunctionPass {
44   using IntervalMapTy = std::map<BasicBlock *, Interval *>;
45   IntervalMapTy IntervalMap;
46 
47   using IntervalListTy = std::vector<Interval *>;
48   Interval *RootInterval = nullptr;
49   std::vector<Interval *> Intervals;
50 
51 public:
52   static char ID; // Pass identification, replacement for typeid
53 
IntervalPartition()54   IntervalPartition() : FunctionPass(ID) {
55     initializeIntervalPartitionPass(*PassRegistry::getPassRegistry());
56   }
57 
58   // run - Calculate the interval partition for this function
59   bool runOnFunction(Function &F) override;
60 
61   // IntervalPartition ctor - Build a reduced interval partition from an
62   // existing interval graph.  This takes an additional boolean parameter to
63   // distinguish it from a copy constructor.  Always pass in false for now.
64   IntervalPartition(IntervalPartition &I, bool);
65 
66   // print - Show contents in human readable format...
67   void print(raw_ostream &O, const Module* = nullptr) const override;
68 
69   // getRootInterval() - Return the root interval that contains the starting
70   // block of the function.
getRootInterval()71   inline Interval *getRootInterval() { return RootInterval; }
72 
73   // isDegeneratePartition() - Returns true if the interval partition contains
74   // a single interval, and thus cannot be simplified anymore.
isDegeneratePartition()75   bool isDegeneratePartition() { return Intervals.size() == 1; }
76 
77   // TODO: isIrreducible - look for triangle graph.
78 
79   // getBlockInterval - Return the interval that a basic block exists in.
getBlockInterval(BasicBlock * BB)80   inline Interval *getBlockInterval(BasicBlock *BB) {
81     IntervalMapTy::iterator I = IntervalMap.find(BB);
82     return I != IntervalMap.end() ? I->second : nullptr;
83   }
84 
85   // getAnalysisUsage - Implement the Pass API
getAnalysisUsage(AnalysisUsage & AU)86   void getAnalysisUsage(AnalysisUsage &AU) const override {
87     AU.setPreservesAll();
88   }
89 
90   // Interface to Intervals vector...
getIntervals()91   const std::vector<Interval*> &getIntervals() const { return Intervals; }
92 
93   // releaseMemory - Reset state back to before function was analyzed
94   void releaseMemory() override;
95 
96 private:
97   // addIntervalToPartition - Add an interval to the internal list of intervals,
98   // and then add mappings from all of the basic blocks in the interval to the
99   // interval itself (in the IntervalMap).
100   void addIntervalToPartition(Interval *I);
101 
102   // updatePredecessors - Interval generation only sets the successor fields of
103   // the interval data structures.  After interval generation is complete,
104   // run through all of the intervals and propagate successor info as
105   // predecessor info.
106   void updatePredecessors(Interval *Int);
107 };
108 
109 } // end namespace llvm
110 
111 #endif // LLVM_ANALYSIS_INTERVALPARTITION_H
112