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//===-- llvm/ADT/IntEqClasses.h - Equiv. Classes of Integers ----*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
///
/// \file
/// Equivalence classes for small integers. This is a mapping of the integers
/// 0 .. N-1 into M equivalence classes numbered 0 .. M-1.
///
/// Initially each integer has its own equivalence class. Classes are joined by
/// passing a representative member of each class to join().
///
/// Once the classes are built, compress() will number them 0 .. M-1 and prevent
/// further changes.
///
//===----------------------------------------------------------------------===//
#ifndef LLVM_ADT_INTEQCLASSES_H
#define LLVM_ADT_INTEQCLASSES_H
#include "llvm/ADT/SmallVector.h"
namespace llvm {
class IntEqClasses {
/// EC - When uncompressed, map each integer to a smaller member of its
/// equivalence class. The class leader is the smallest member and maps to
/// itself.
///
/// When compressed, EC[i] is the equivalence class of i.
SmallVector<unsigned, 8> EC;
/// NumClasses - The number of equivalence classes when compressed, or 0 when
/// uncompressed.
unsigned NumClasses = 0;
public:
/// IntEqClasses - Create an equivalence class mapping for 0 .. N-1.
IntEqClasses(unsigned N = 0) { grow(N); }
/// grow - Increase capacity to hold 0 .. N-1, putting new integers in unique
/// equivalence classes.
/// This requires an uncompressed map.
void grow(unsigned N);
/// clear - Clear all classes so that grow() will assign a unique class to
/// every integer.
void clear() {
EC.clear();
NumClasses = 0;
}
/// Join the equivalence classes of a and b. After joining classes,
/// findLeader(a) == findLeader(b). This requires an uncompressed map.
/// Returns the new leader.
unsigned join(unsigned a, unsigned b);
/// findLeader - Compute the leader of a's equivalence class. This is the
/// smallest member of the class.
/// This requires an uncompressed map.
unsigned findLeader(unsigned a) const;
/// compress - Compress equivalence classes by numbering them 0 .. M.
/// This makes the equivalence class map immutable.
void compress();
/// getNumClasses - Return the number of equivalence classes after compress()
/// was called.
unsigned getNumClasses() const { return NumClasses; }
/// operator[] - Return a's equivalence class number, 0 .. getNumClasses()-1.
/// This requires a compressed map.
unsigned operator[](unsigned a) const {
assert(NumClasses && "operator[] called before compress()");
return EC[a];
}
/// uncompress - Change back to the uncompressed representation that allows
/// editing.
void uncompress();
};
} // End llvm namespace
#endif
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