78 lines
2.2 KiB
C++
78 lines
2.2 KiB
C++
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//===-- llvm/ADT/IntEqClasses.cpp - Equivalence Classes of Integers -------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// Equivalence classes for small integers. This is a mapping of the integers
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// 0 .. N-1 into M equivalence classes numbered 0 .. M-1.
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//
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// Initially each integer has its own equivalence class. Classes are joined by
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// passing a representative member of each class to join().
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//
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// Once the classes are built, compress() will number them 0 .. M-1 and prevent
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// further changes.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/ADT/IntEqClasses.h"
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#include <cassert>
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using namespace llvm;
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void IntEqClasses::grow(unsigned N) {
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assert(NumClasses == 0 && "grow() called after compress().");
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EC.reserve(N);
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while (EC.size() < N)
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EC.push_back(EC.size());
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}
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unsigned IntEqClasses::join(unsigned a, unsigned b) {
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assert(NumClasses == 0 && "join() called after compress().");
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unsigned eca = EC[a];
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unsigned ecb = EC[b];
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// Update pointers while searching for the leaders, compressing the paths
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// incrementally. The larger leader will eventually be updated, joining the
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// classes.
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while (eca != ecb)
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if (eca < ecb) {
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EC[b] = eca;
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b = ecb;
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ecb = EC[b];
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} else {
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EC[a] = ecb;
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a = eca;
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eca = EC[a];
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}
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return eca;
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}
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unsigned IntEqClasses::findLeader(unsigned a) const {
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assert(NumClasses == 0 && "findLeader() called after compress().");
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while (a != EC[a])
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a = EC[a];
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return a;
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}
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void IntEqClasses::compress() {
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if (NumClasses)
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return;
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for (unsigned i = 0, e = EC.size(); i != e; ++i)
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EC[i] = (EC[i] == i) ? NumClasses++ : EC[EC[i]];
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}
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void IntEqClasses::uncompress() {
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if (!NumClasses)
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return;
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SmallVector<unsigned, 8> Leader;
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for (unsigned i = 0, e = EC.size(); i != e; ++i)
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if (EC[i] < Leader.size())
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EC[i] = Leader[EC[i]];
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else
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Leader.push_back(EC[i] = i);
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NumClasses = 0;
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}
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