1 //===- MarkLive.cpp -------------------------------------------------------===// 2 // 3 // The LLVM Linker 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 10 #include "Chunks.h" 11 #include "Symbols.h" 12 #include "lld/Common/Timer.h" 13 #include "llvm/ADT/STLExtras.h" 14 #include <vector> 15 16 namespace lld { 17 namespace coff { 18 19 static Timer GCTimer("GC", Timer::root()); 20 21 // Set live bit on for each reachable chunk. Unmarked (unreachable) 22 // COMDAT chunks will be ignored by Writer, so they will be excluded 23 // from the final output. 24 void markLive(ArrayRef<Chunk *> Chunks) { 25 ScopedTimer T(GCTimer); 26 27 // We build up a worklist of sections which have been marked as live. We only 28 // push into the worklist when we discover an unmarked section, and we mark 29 // as we push, so sections never appear twice in the list. 30 SmallVector<SectionChunk *, 256> Worklist; 31 32 // COMDAT section chunks are dead by default. Add non-COMDAT chunks. 33 for (Chunk *C : Chunks) 34 if (auto *SC = dyn_cast<SectionChunk>(C)) 35 if (SC->Live) 36 Worklist.push_back(SC); 37 38 auto Enqueue = [&](SectionChunk *C) { 39 if (C->Live) 40 return; 41 C->Live = true; 42 Worklist.push_back(C); 43 }; 44 45 auto AddSym = [&](Symbol *B) { 46 if (auto *Sym = dyn_cast<DefinedRegular>(B)) 47 Enqueue(Sym->getChunk()); 48 else if (auto *Sym = dyn_cast<DefinedImportData>(B)) 49 Sym->File->Live = true; 50 else if (auto *Sym = dyn_cast<DefinedImportThunk>(B)) 51 Sym->WrappedSym->File->Live = Sym->WrappedSym->File->ThunkLive = true; 52 }; 53 54 // Add GC root chunks. 55 for (Symbol *B : Config->GCRoot) 56 AddSym(B); 57 58 while (!Worklist.empty()) { 59 SectionChunk *SC = Worklist.pop_back_val(); 60 assert(SC->Live && "We mark as live when pushing onto the worklist!"); 61 62 // Mark all symbols listed in the relocation table for this section. 63 for (Symbol *B : SC->symbols()) 64 if (B) 65 AddSym(B); 66 67 // Mark associative sections if any. 68 for (SectionChunk *C : SC->children()) 69 Enqueue(C); 70 } 71 } 72 73 } 74 } 75