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//===- MarkLive.cpp -------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "COFFLinkerContext.h"
#include "Chunks.h"
#include "Symbols.h"
#include "lld/Common/Timer.h"
#include "llvm/Support/TimeProfiler.h"
namespace lld::coff {
// Set live bit on for each reachable chunk. Unmarked (unreachable)
// COMDAT chunks will be ignored by Writer, so they will be excluded
// from the final output.
void markLive(COFFLinkerContext &ctx) {
llvm::TimeTraceScope timeScope("Mark live");
ScopedTimer t(ctx.gcTimer);
// We build up a worklist of sections which have been marked as live. We only
// push into the worklist when we discover an unmarked section, and we mark
// as we push, so sections never appear twice in the list.
SmallVector<SectionChunk *, 256> worklist;
// COMDAT section chunks are dead by default. Add non-COMDAT chunks. Do not
// traverse DWARF sections. They are live, but they should not keep other
// sections alive.
for (Chunk *c : ctx.driver.getChunks())
if (auto *sc = dyn_cast<SectionChunk>(c))
if (sc->live && !sc->isDWARF())
worklist.push_back(sc);
auto enqueue = [&](SectionChunk *c) {
if (c->live)
return;
c->live = true;
worklist.push_back(c);
};
std::function<void(Symbol *)> addSym;
auto addImportFile = [&](ImportFile *file) {
file->live = true;
if (file->impchkThunk && file->impchkThunk->exitThunk)
addSym(file->impchkThunk->exitThunk);
};
addSym = [&](Symbol *s) {
Defined *b = s->getDefined();
if (!b)
return;
if (auto *sym = dyn_cast<DefinedRegular>(b)) {
enqueue(sym->getChunk());
} else if (auto *sym = dyn_cast<DefinedImportData>(b)) {
addImportFile(sym->file);
} else if (auto *sym = dyn_cast<DefinedImportThunk>(b)) {
addImportFile(sym->wrappedSym->file);
sym->getChunk()->live = true;
}
};
// Add GC root chunks.
for (Symbol *b : ctx.config.gcroot)
addSym(b);
while (!worklist.empty()) {
SectionChunk *sc = worklist.pop_back_val();
assert(sc->live && "We mark as live when pushing onto the worklist!");
// Mark all symbols listed in the relocation table for this section.
for (Symbol *b : sc->symbols())
if (b)
addSym(b);
// Mark associative sections if any.
for (SectionChunk &c : sc->children())
enqueue(&c);
// Mark EC entry thunks.
if (Defined *entryThunk = sc->getEntryThunk())
addSym(entryThunk);
}
}
}
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