1 //===-- llvm/ADT/IntEqClasses.h - Equiv. Classes of Integers ----*- 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 // Equivalence classes for small integers. This is a mapping of the integers
11 // 0 .. N-1 into M equivalence classes numbered 0 .. M-1.
12 //
13 // Initially each integer has its own equivalence class. Classes are joined by
14 // passing a representative member of each class to join().
15 //
16 // Once the classes are built, compress() will number them 0 .. M-1 and prevent
17 // further changes.
18 //
19 //===----------------------------------------------------------------------===//
20 
21 #ifndef LLVM_ADT_INTEQCLASSES_H
22 #define LLVM_ADT_INTEQCLASSES_H
23 
24 #include "llvm/ADT/SmallVector.h"
25 
26 namespace llvm {
27 
28 class IntEqClasses {
29   /// EC - When uncompressed, map each integer to a smaller member of its
30   /// equivalence class. The class leader is the smallest member and maps to
31   /// itself.
32   ///
33   /// When compressed, EC[i] is the equivalence class of i.
34   SmallVector<unsigned, 8> EC;
35 
36   /// NumClasses - The number of equivalence classes when compressed, or 0 when
37   /// uncompressed.
38   unsigned NumClasses;
39 
40 public:
41   /// IntEqClasses - Create an equivalence class mapping for 0 .. N-1.
42   IntEqClasses(unsigned N = 0) : NumClasses(0) { grow(N); }
43 
44   /// grow - Increase capacity to hold 0 .. N-1, putting new integers in unique
45   /// equivalence classes.
46   /// This requires an uncompressed map.
47   void grow(unsigned N);
48 
49   /// clear - Clear all classes so that grow() will assign a unique class to
50   /// every integer.
clear()51   void clear() {
52     EC.clear();
53     NumClasses = 0;
54   }
55 
56   /// join - Join the equivalence classes of a and b. After joining classes,
57   /// findLeader(a) == findLeader(b).
58   /// This requires an uncompressed map.
59   void join(unsigned a, unsigned b);
60 
61   /// findLeader - Compute the leader of a's equivalence class. This is the
62   /// smallest member of the class.
63   /// This requires an uncompressed map.
64   unsigned findLeader(unsigned a) const;
65 
66   /// compress - Compress equivalence classes by numbering them 0 .. M.
67   /// This makes the equivalence class map immutable.
68   void compress();
69 
70   /// getNumClasses - Return the number of equivalence classes after compress()
71   /// was called.
getNumClasses()72   unsigned getNumClasses() const { return NumClasses; }
73 
74   /// operator[] - Return a's equivalence class number, 0 .. getNumClasses()-1.
75   /// This requires a compressed map.
76   unsigned operator[](unsigned a) const {
77     assert(NumClasses && "operator[] called before compress()");
78     return EC[a];
79   }
80 
81   /// uncompress - Change back to the uncompressed representation that allows
82   /// editing.
83   void uncompress();
84 };
85 
86 } // End llvm namespace
87 
88 #endif
89