[lld] [lld][ELF] Extend profile guided function ordering to ELF binaries (PR #117514)

[Ellis Hoag via llvm-commits]

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@@ -0,0 +1,383 @@
+//===- BPSectionOrdererBase.cpp---------------------------------------*- C++
+//-*-===//
+//
+// 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 "lld/Common/BPSectionOrdererBase.h"
+#include "lld/Common/ErrorHandler.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/DenseSet.h"
+#include "llvm/ADT/SetVector.h"
+#include "llvm/ADT/SmallSet.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/StringMap.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/ProfileData/InstrProfReader.h"
+#include "llvm/Support/BalancedPartitioning.h"
+#include "llvm/Support/TimeProfiler.h"
+#include "llvm/Support/VirtualFileSystem.h"
+#include "llvm/Support/xxhash.h"
+
+#define DEBUG_TYPE "bp-section-orderer"
+using namespace llvm;
+using UtilityNodes = SmallVector<BPFunctionNode::UtilityNodeT>;
+
+namespace lld {
+
+static SmallVector<std::pair<unsigned, UtilityNodes>> getUnsForCompression(
+    ArrayRef<const BPSectionBase *> sections,
+    const DenseMap<const BPSectionBase *, uint64_t> &sectionToIdx,
+    ArrayRef<unsigned> sectionIdxs,
+    DenseMap<unsigned, SmallVector<unsigned>> *duplicateSectionIdxs,
+    BPFunctionNode::UtilityNodeT &maxUN) {
+  TimeTraceScope timeScope("Build nodes for compression");
+
+  SmallVector<std::pair<unsigned, SmallVector<uint64_t>>> sectionHashes;
+  sectionHashes.reserve(sectionIdxs.size());
+  SmallVector<uint64_t> hashes;
+
+  for (unsigned sectionIdx : sectionIdxs) {
+    const auto *isec = sections[sectionIdx];
+    isec->getSectionHash(hashes, sectionToIdx);
+    sectionHashes.emplace_back(sectionIdx, std::move(hashes));
+    hashes.clear();
+  }
+
+  DenseMap<uint64_t, unsigned> hashFrequency;
+  for (auto &[sectionIdx, hashes] : sectionHashes)
+    for (auto hash : hashes)
+      ++hashFrequency[hash];
+
+  if (duplicateSectionIdxs) {
+    // Merge section that are nearly identical
----------------
ellishg wrote:

```suggestion
    // Merge sections that are nearly identical
```

https://github.com/llvm/llvm-project/pull/117514