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//===- ICF.cpp ------------------------------------------------------------===//
//
// The LLVM Linker
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// Implements ICF (Identical COMDAT Folding)
//
//===----------------------------------------------------------------------===//
#include "Chunks.h"
#include <tuple>
#include <unordered_set>
#include <vector>
namespace lld {
namespace coff {
namespace {
struct Hasher {
size_t operator()(const SectionChunk *C) const { return C->getHash(); }
};
struct Equals {
bool operator()(const SectionChunk *A, const SectionChunk *B) const {
return A->equals(B);
}
};
} // anonymous namespace
// Merge identical COMDAT sections.
// Two sections are considered as identical when their section headers,
// contents and relocations are all the same.
void doICF(const std::vector<Chunk *> &Chunks) {
std::unordered_set<SectionChunk *, Hasher, Equals> Set;
bool Redo;
do {
Set.clear();
Redo = false;
for (Chunk *C : Chunks) {
auto *SC = dyn_cast<SectionChunk>(C);
if (!SC || !SC->isCOMDAT() || !SC->isLive())
continue;
auto P = Set.insert(SC);
bool Inserted = P.second;
if (Inserted)
continue;
SectionChunk *Existing = *P.first;
SC->replaceWith(Existing);
// By merging sections, two relocations that originally pointed to
// different locations can now point to the same location.
// So, repeat the process until a convegence is obtained.
Redo = true;
}
} while (Redo);
}
} // namespace coff
} // namespace lld
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