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 /// \file
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.
51   void clear() {
52     EC.clear();
53     NumClasses = 0;
54   }
55 
56   /// Join the equivalence classes of a and b. After joining classes,
57   /// findLeader(a) == findLeader(b). This requires an uncompressed map.
58   /// Returns the new leader.
59   unsigned 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.
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