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1 //===- MarkLive.cpp -------------------------------------------------------===//
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2 //
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3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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4 // See https://llvm.org/LICENSE.txt for license information.
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5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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6 //
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7 //===----------------------------------------------------------------------===//
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8
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9 #include "Chunks.h"
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10 #include "Symbols.h"
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11 #include "lld/Common/Timer.h"
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12 #include "llvm/ADT/STLExtras.h"
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13 #include <vector>
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14
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15 namespace lld {
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16 namespace coff {
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17
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18 static Timer gctimer("GC", Timer::root());
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19
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20 // Set live bit on for each reachable chunk. Unmarked (unreachable)
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21 // COMDAT chunks will be ignored by Writer, so they will be excluded
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22 // from the final output.
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23 void markLive(ArrayRef<Chunk *> chunks) {
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24 ScopedTimer t(gctimer);
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25
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26 // We build up a worklist of sections which have been marked as live. We only
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27 // push into the worklist when we discover an unmarked section, and we mark
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28 // as we push, so sections never appear twice in the list.
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29 SmallVector<SectionChunk *, 256> worklist;
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30
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173
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31 // COMDAT section chunks are dead by default. Add non-COMDAT chunks. Do not
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32 // traverse DWARF sections. They are live, but they should not keep other
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33 // sections alive.
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34 for (Chunk *c : chunks)
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35 if (auto *sc = dyn_cast<SectionChunk>(c))
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36 if (sc->live && !sc->isDWARF())
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37 worklist.push_back(sc);
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38
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39 auto enqueue = [&](SectionChunk *c) {
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40 if (c->live)
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41 return;
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42 c->live = true;
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43 worklist.push_back(c);
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44 };
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45
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46 auto addSym = [&](Symbol *b) {
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47 if (auto *sym = dyn_cast<DefinedRegular>(b))
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48 enqueue(sym->getChunk());
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49 else if (auto *sym = dyn_cast<DefinedImportData>(b))
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50 sym->file->live = true;
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51 else if (auto *sym = dyn_cast<DefinedImportThunk>(b))
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52 sym->wrappedSym->file->live = sym->wrappedSym->file->thunkLive = true;
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53 };
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54
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55 // Add GC root chunks.
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56 for (Symbol *b : config->gcroot)
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57 addSym(b);
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58
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59 while (!worklist.empty()) {
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60 SectionChunk *sc = worklist.pop_back_val();
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61 assert(sc->live && "We mark as live when pushing onto the worklist!");
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62
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63 // Mark all symbols listed in the relocation table for this section.
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64 for (Symbol *b : sc->symbols())
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65 if (b)
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66 addSym(b);
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67
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68 // Mark associative sections if any.
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69 for (SectionChunk &c : sc->children())
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70 enqueue(&c);
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71 }
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72 }
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73
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74 }
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75 }
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