[lld] [LLD][ELF] add bp-* options in ELF (PR #120514)

[Fangrui Song via llvm-commits]

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@@ -0,0 +1,134 @@
+//===- BPSectionOrderer.h -------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+///
+/// This file uses Balanced Partitioning to order sections to improve startup
+/// time and compressed size.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLD_ELF_BPSECTION_ORDERER_H
+#define LLD_ELF_BPSECTION_ORDERER_H
+
+#include "InputFiles.h"
+#include "InputSection.h"
+#include "Relocations.h"
+#include "Symbols.h"
+#include "lld/Common/BPSectionOrdererBase.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/BinaryFormat/ELF.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/xxhash.h"
+
+namespace lld::elf {
+
+class InputSection;
+
+class BPSymbolELF : public BPSymbol {
+  const Symbol *sym;
+
+public:
+  explicit BPSymbolELF(const Symbol *s) : sym(s) {}
+
+  llvm::StringRef getName() const override { return sym->getName(); }
+
+  const Defined *asDefined() const {
+    return llvm::dyn_cast_or_null<Defined>(sym);
+  }
+
+  std::optional<uint64_t> getValue() const override {
+    if (auto *d = asDefined())
+      return d->value;
+    return {};
+  }
+
+  std::optional<uint64_t> getSize() const override {
+    if (auto *d = asDefined())
+      return d->size;
+    return {};
+  }
+
+  InputSectionBase *getInputSection() const {
+    if (auto *d = asDefined())
+      return llvm::dyn_cast_or_null<InputSectionBase>(d->section);
+    return nullptr;
+  }
+
+  const Symbol *getSymbol() const { return sym; }
+};
+
+class BPSectionELF : public BPSectionBase {
+  const InputSectionBase *isec;
+  std::unique_ptr<BPSymbolELF> symbol;
+
+public:
+  explicit BPSectionELF(const InputSectionBase *sec,
+                        std::unique_ptr<BPSymbolELF> sym)
+      : isec(sec), symbol(std::move(sym)) {}
+
+  const void *getSection() const override { return isec; }
+
+  uint64_t getSize() const override { return isec->getSize(); }
+
+  bool isCodeSection() const override {
+    return isec->flags & llvm::ELF::SHF_EXECINSTR;
+  }
+
+  bool hasValidData() const override {
+    return isec && !isec->content().empty();
+  }
+
+  SmallVector<std::unique_ptr<BPSymbol>> getSymbols() const override {
+    SmallVector<std::unique_ptr<BPSymbol>> symbols;
+    if (auto *d = symbol->asDefined())
+      symbols.emplace_back(std::make_unique<BPSymbolELF>(d));
+    return symbols;
+  }
+
+  std::optional<StringRef>
+  getResolvedLinkageName(llvm::StringRef name) const override {
+    return {};
+  }
+
+  void getSectionHashes(llvm::SmallVectorImpl<uint64_t> &hashes,
+                        const llvm::DenseMap<const void *, uint64_t>
+                            &sectionToIdx) const override {
+    constexpr unsigned windowSize = 4;
+
+    // Calculate content hashes
+    size_t size = isec->content().size();
+    for (size_t i = 0; i < size; i++) {
+      auto window = isec->content().drop_front(i).take_front(windowSize);
+      hashes.push_back(xxHash64(window));
----------------
MaskRay wrote:

I am surprised that `xxHash64` doesn't need to be qualified.

This complex function should be moved toto BPSectionOrderer.cpp

why take_front windowSize?

https://github.com/llvm/llvm-project/pull/120514