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