include/llvm/ADT/IntEqClasses.h

   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