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ICF runs before BPSectionOrderer. When a section is ICF'ed, it seems that the original sections are marked as not live, but are still kept around. Prior to this patch, those ICF'ed sections would be passed to BP and ordered before being skipped when writing the output. Now, these sections are no longer passed to BP, saving runtime and possibly improving BP's output. In a large binary, I found that the number of sections ordered using BP decreased, while the number of duplicate sections drastically decreased as expected. ``` Functions for startup: 50755 -> 50520 Functions for compression: 165734 -> 105328 Duplicate functions: 1827231 -> 55230 ```
99 lines
3.6 KiB
C++
99 lines
3.6 KiB
C++
//===- BPSectionOrderer.cpp -----------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#include "BPSectionOrderer.h"
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#include "InputFiles.h"
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#include "InputSection.h"
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#include "SymbolTable.h"
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#include "Symbols.h"
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#include "lld/Common/BPSectionOrdererBase.inc"
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#include "llvm/Support/Endian.h"
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using namespace llvm;
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using namespace lld::elf;
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namespace {
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struct BPOrdererELF;
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}
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template <> struct lld::BPOrdererTraits<struct BPOrdererELF> {
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using Section = elf::InputSectionBase;
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using Defined = elf::Defined;
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};
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namespace {
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struct BPOrdererELF : lld::BPOrderer<BPOrdererELF> {
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DenseMap<const InputSectionBase *, Defined *> secToSym;
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static uint64_t getSize(const Section &sec) { return sec.getSize(); }
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static bool isCodeSection(const Section &sec) {
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return sec.flags & ELF::SHF_EXECINSTR;
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}
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ArrayRef<Defined *> getSymbols(const Section &sec) {
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auto it = secToSym.find(&sec);
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if (it == secToSym.end())
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return {};
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return ArrayRef(it->second);
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}
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static void
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getSectionHashes(const Section &sec, SmallVectorImpl<uint64_t> &hashes,
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const DenseMap<const void *, uint64_t> §ionToIdx) {
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constexpr unsigned windowSize = 4;
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// Calculate content hashes: k-mers and the last k-1 bytes.
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ArrayRef<uint8_t> data = sec.content();
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if (data.size() >= windowSize)
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for (size_t i = 0; i <= data.size() - windowSize; ++i)
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hashes.push_back(support::endian::read32le(data.data() + i));
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for (uint8_t byte : data.take_back(windowSize - 1))
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hashes.push_back(byte);
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llvm::sort(hashes);
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hashes.erase(std::unique(hashes.begin(), hashes.end()), hashes.end());
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}
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static StringRef getSymName(const Defined &sym) { return sym.getName(); }
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static uint64_t getSymValue(const Defined &sym) { return sym.value; }
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static uint64_t getSymSize(const Defined &sym) { return sym.size; }
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};
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} // namespace
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DenseMap<const InputSectionBase *, int> elf::runBalancedPartitioning(
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Ctx &ctx, StringRef profilePath, bool forFunctionCompression,
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bool forDataCompression, bool compressionSortStartupFunctions,
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bool verbose) {
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// Collect candidate sections and associated symbols.
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SmallVector<InputSectionBase *> sections;
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DenseMap<CachedHashStringRef, std::set<unsigned>> rootSymbolToSectionIdxs;
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BPOrdererELF orderer;
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auto addSection = [&](Symbol &sym) {
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auto *d = dyn_cast<Defined>(&sym);
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if (!d)
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return;
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auto *sec = dyn_cast_or_null<InputSection>(d->section);
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// Skip empty, discarded, ICF folded sections. Skipping ICF folded sections
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// reduces duplicate detection work in BPSectionOrderer.
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if (!sec || sec->size == 0 || !sec->isLive() || sec->repl != sec ||
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!orderer.secToSym.try_emplace(sec, d).second)
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return;
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rootSymbolToSectionIdxs[CachedHashStringRef(getRootSymbol(sym.getName()))]
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.insert(sections.size());
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sections.emplace_back(sec);
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};
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for (Symbol *sym : ctx.symtab->getSymbols())
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addSection(*sym);
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for (ELFFileBase *file : ctx.objectFiles)
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for (Symbol *sym : file->getLocalSymbols())
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addSection(*sym);
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return orderer.computeOrder(profilePath, forFunctionCompression,
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forDataCompression,
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compressionSortStartupFunctions, verbose,
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sections, rootSymbolToSectionIdxs);
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}
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