1 //===-- llvm/ADT/IntEqClasses.h - Equiv. Classes of Integers ----*- 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 // Equivalence classes for small integers. This is a mapping of the integers
10 // 0 .. N-1 into M equivalence classes numbered 0 .. M-1.
11 //
12 // Initially each integer has its own equivalence class. Classes are joined by
13 // passing a representative member of each class to join().
14 //
15 // Once the classes are built, compress() will number them 0 .. M-1 and prevent
16 // further changes.
17 //
18 //===----------------------------------------------------------------------===//
19 
20 #ifndef LLVM_ADT_INTEQCLASSES_H
21 #define LLVM_ADT_INTEQCLASSES_H
22 
23 #include "llvm/ADT/SmallVector.h"
24 
25 namespace llvm {
26 
27 class IntEqClasses {
28   /// EC - When uncompressed, map each integer to a smaller member of its
29   /// equivalence class. The class leader is the smallest member and maps to
30   /// itself.
31   ///
32   /// When compressed, EC[i] is the equivalence class of i.
33   SmallVector<unsigned, 8> EC;
34 
35   /// NumClasses - The number of equivalence classes when compressed, or 0 when
36   /// uncompressed.
37   unsigned NumClasses;
38 
39 public:
40   /// IntEqClasses - Create an equivalence class mapping for 0 .. N-1.
41   IntEqClasses(unsigned N = 0) : NumClasses(0) { grow(N); }
42 
43   /// grow - Increase capacity to hold 0 .. N-1, putting new integers in unique
44   /// equivalence classes.
45   /// This requires an uncompressed map.
46   void grow(unsigned N);
47 
48   /// clear - Clear all classes so that grow() will assign a unique class to
49   /// every integer.
50   void clear() {
51     EC.clear();
52     NumClasses = 0;
53   }
54 
55   /// Join the equivalence classes of a and b. After joining classes,
56   /// findLeader(a) == findLeader(b). This requires an uncompressed map.
57   /// Returns the new leader.
58   unsigned join(unsigned a, unsigned b);
59 
60   /// findLeader - Compute the leader of a's equivalence class. This is the
61   /// smallest member of the class.
62   /// This requires an uncompressed map.
63   unsigned findLeader(unsigned a) const;
64 
65   /// compress - Compress equivalence classes by numbering them 0 .. M.
66   /// This makes the equivalence class map immutable.
67   void compress();
68 
69   /// getNumClasses - Return the number of equivalence classes after compress()
70   /// was called.
71   unsigned getNumClasses() const { return NumClasses; }
72 
73   /// operator[] - Return a's equivalence class number, 0 .. getNumClasses()-1.
74   /// This requires a compressed map.
75   unsigned operator[](unsigned a) const {
76     assert(NumClasses && "operator[] called before compress()");
77     return EC[a];
78   }
79 
80   /// uncompress - Change back to the uncompressed representation that allows
81   /// editing.
82   void uncompress();
83 };
84 
85 } // End llvm namespace
86 
87 #endif
88