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| 1 | //===-- IntervalSet.h -------------------------------------------*- 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 | #ifndef FORTRAN_LOWER_INTERVALSET_H |
| 10 | #define FORTRAN_LOWER_INTERVALSET_H |
| 11 | |
| 12 | #include <cassert> |
| 13 | #include <map> |
| 14 | |
| 15 | namespace Fortran::lower { |
| 16 | |
| 17 | //===----------------------------------------------------------------------===// |
| 18 | // Interval set |
| 19 | //===----------------------------------------------------------------------===// |
| 20 | |
| 21 | /// Interval set to keep track of intervals, merging them when they overlap one |
| 22 | /// another. Used to refine the pseudo-offset ranges of the front-end symbols |
| 23 | /// into groups of aliasing variables. |
| 24 | struct IntervalSet { |
| 25 | using MAP = std::map<std::size_t, std::size_t>; |
| 26 | using Iterator = MAP::const_iterator; |
| 27 | |
| 28 | // Handles the merging of overlapping intervals correctly, efficiently. |
| 29 | void merge(std::size_t lo, std::size_t up) { |
| 30 | assert(lo <= up); |
| 31 | if (empty()) { |
| 32 | m.insert({lo, up}); |
| 33 | return; |
| 34 | } |
| 35 | auto i = m.lower_bound(lo); |
| 36 | // i->first >= lo |
| 37 | if (i == begin()) { |
| 38 | if (up < i->first) { |
| 39 | // [lo..up] < i->first |
| 40 | m.insert({lo, up}); |
| 41 | return; |
| 42 | } |
| 43 | // up >= i->first |
| 44 | if (i->second > up) |
| 45 | up = i->second; |
| 46 | fuse(lo, up, i); |
| 47 | return; |
| 48 | } |
| 49 | auto i1 = i; |
| 50 | if (i == end() || i->first > lo) |
| 51 | i = std::prev(i); |
| 52 | // i->first <= lo |
| 53 | if (i->second >= up) { |
| 54 | // i->first <= lo && up <= i->second, keep i |
| 55 | return; |
| 56 | } |
| 57 | // i->second < up |
| 58 | if (i->second < lo) { |
| 59 | if (i1 == end() || i1->first > up) { |
| 60 | // i < [lo..up] < i1 |
| 61 | m.insert({lo, up}); |
| 62 | return; |
| 63 | } |
| 64 | // i < [lo..up], i1->first <= up --> [lo..up] union [i1..?] |
| 65 | i = i1; |
| 66 | } else { |
| 67 | // i->first <= lo, lo <= i->second --> [i->first..up] union [i..?] |
| 68 | lo = i->first; |
| 69 | } |
| 70 | fuse(lo, up, i); |
| 71 | } |
| 72 | |
| 73 | Iterator find(std::size_t pt) const { |
| 74 | auto i = m.lower_bound(pt); |
| 75 | if (i != end() && i->first == pt) |
| 76 | return i; |
| 77 | if (i == begin()) |
| 78 | return end(); |
| 79 | i = std::prev(i); |
| 80 | if (i->second < pt) |
| 81 | return end(); |
| 82 | return i; |
| 83 | } |
| 84 | |
| 85 | Iterator begin() const { return m.begin(); } |
| 86 | Iterator end() const { return m.end(); } |
| 87 | bool empty() const { return m.empty(); } |
| 88 | std::size_t size() const { return m.size(); } |
| 89 | |
| 90 | private: |
| 91 | // Find and fuse overlapping sets. |
| 92 | void fuse(std::size_t lo, std::size_t up, Iterator i) { |
| 93 | auto j = m.upper_bound(up); |
| 94 | // up < j->first |
| 95 | std::size_t cu = std::prev(j)->second; |
| 96 | // cu < j->first |
| 97 | if (cu > up) |
| 98 | up = cu; |
| 99 | m.erase(i, j); |
| 100 | // merge [i .. j) with [i->first, max(up, cu)] |
| 101 | m.insert({lo, up}); |
| 102 | } |
| 103 | |
| 104 | MAP m{}; |
| 105 | }; |
| 106 | |
| 107 | } // namespace Fortran::lower |
| 108 | |
| 109 | #endif // FORTRAN_LOWER_INTERVALSET_H |
| 110 |
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