| 1 | // Obstack-related utilities. |
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| 2 | // Copyright (C) 2020-2023 Free Software Foundation, Inc. |
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| 3 | // |
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| 4 | // This file is part of GCC. |
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| 5 | // |
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| 6 | // GCC is free software; you can redistribute it and/or modify it under |
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| 7 | // the terms of the GNU General Public License as published by the Free |
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| 8 | // Software Foundation; either version 3, or (at your option) any later |
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| 9 | // version. |
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| 10 | // |
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| 11 | // GCC is distributed in the hope that it will be useful, but WITHOUT ANY |
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| 12 | // WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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| 13 | // FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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| 14 | // for more details. |
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| 15 | // |
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| 16 | // You should have received a copy of the GNU General Public License |
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| 17 | // along with GCC; see the file COPYING3. If not see |
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| 18 | // <http://www.gnu.org/licenses/>. |
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| 19 | |
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| 20 | #ifndef GCC_OBSTACK_UTILS_H |
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| 21 | #define GCC_OBSTACK_UTILS_H |
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| 22 | |
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| 23 | // This RAII class automatically frees memory allocated on an obstack, |
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| 24 | // unless told not to via keep (). It automatically converts to an |
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| 25 | // obstack, so it can (optionally) be used in place of the obstack |
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| 26 | // to make the scoping clearer. For example: |
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| 27 | // |
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| 28 | // obstack_watermark watermark (ob); |
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| 29 | // auto *ptr1 = XOBNEW (watermark, struct1); |
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| 30 | // if (...) |
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| 31 | // // Frees ptr1. |
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| 32 | // return false; |
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| 33 | // |
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| 34 | // auto *ptr2 = XOBNEW (watermark, struct2); |
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| 35 | // if (...) |
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| 36 | // // Frees ptr1 and ptr2. |
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| 37 | // return false; |
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| 38 | // |
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| 39 | // // Retains ptr1 and ptr2. |
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| 40 | // watermark.keep (); |
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| 41 | // |
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| 42 | // auto *ptr3 = XOBNEW (watermark, struct3); |
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| 43 | // if (...) |
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| 44 | // // Frees ptr3. |
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| 45 | // return false; |
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| 46 | // |
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| 47 | // // Retains ptr3 (in addition to ptr1 and ptr2 above). |
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| 48 | // watermark.keep (); |
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| 49 | // return true; |
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| 50 | // |
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| 51 | // The move constructor makes it possible to transfer ownership to a caller: |
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| 52 | // |
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| 53 | // obstack_watermark |
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| 54 | // foo () |
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| 55 | // { |
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| 56 | // obstack_watermark watermark (ob); |
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| 57 | // ... |
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| 58 | // return watermark; |
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| 59 | // } |
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| 60 | // |
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| 61 | // void |
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| 62 | // bar () |
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| 63 | // { |
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| 64 | // // Inherit ownership of everything that foo allocated. |
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| 65 | // obstack_watermark watermark = foo (); |
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| 66 | // ... |
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| 67 | // } |
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| 68 | class obstack_watermark |
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| 69 | { |
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| 70 | public: |
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| 71 | obstack_watermark (obstack *ob) : m_obstack (ob) { keep (); } |
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| 72 | constexpr obstack_watermark (obstack_watermark &&) = default; |
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| 73 | ~obstack_watermark () { obstack_free (m_obstack, m_start); } |
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| 74 | |
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| 75 | operator obstack *() const { return m_obstack; } |
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| 76 | void keep () { m_start = XOBNEWVAR (m_obstack, char, 0); } |
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| 77 | |
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| 78 | private: |
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| 79 | DISABLE_COPY_AND_ASSIGN (obstack_watermark); |
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| 80 | |
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| 81 | protected: |
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| 82 | obstack *m_obstack; |
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| 83 | char *m_start; |
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| 84 | }; |
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| 85 | |
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| 86 | #endif |
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| 87 | |
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