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diff --git a/llvm/lib/CodeGen/MachineFunctionSplitter.cpp b/llvm/lib/CodeGen/MachineFunctionSplitter.cpp
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+++ b/llvm/lib/CodeGen/MachineFunctionSplitter.cpp
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+//===-- MachineFunctionSplitter.cpp - Split machine functions //-----------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// \file
+// Uses profile information to split out cold blocks.
+//
+// This pass splits out cold machine basic blocks from the parent function. This
+// implementation leverages the basic block section framework. Blocks marked
+// cold by this pass are grouped together in a separate section prefixed with
+// ".text.unlikely.*". The linker can then group these together as a cold
+// section. The split part of the function is a contiguous region identified by
+// the symbol "foo.cold". Grouping all cold blocks across functions together
+// decreases fragmentation and improves icache and itlb utilization. Note that
+// the overall changes to the binary size are negligible; only a small number of
+// additional jump instructions may be introduced.
+//
+// For the original RFC of this pass please see
+// https://groups.google.com/d/msg/llvm-dev/RUegaMg-iqc/wFAVxa6fCgAJ
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/ProfileSummaryInfo.h"
+#include "llvm/CodeGen/BasicBlockSectionUtils.h"
+#include "llvm/CodeGen/MachineBasicBlock.h"
+#include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineModuleInfo.h"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Module.h"
+#include "llvm/InitializePasses.h"
+#include "llvm/Support/CommandLine.h"
+
+using namespace llvm;
+
+static cl::opt<unsigned>
+    PercentileCutoff("mfs-psi-cutoff",
+                     cl::desc("Percentile profile summary cutoff used to "
+                              "determine cold blocks. Unused if set to zero."),
+                     cl::init(0), cl::Hidden);
+
+static cl::opt<unsigned> ColdCountThreshold(
+    "mfs-count-threshold",
+    cl::desc(
+        "Minimum number of times a block must be executed to be retained."),
+    cl::init(1), cl::Hidden);
+
+namespace {
+
+class MachineFunctionSplitter : public MachineFunctionPass {
+public:
+  static char ID;
+  MachineFunctionSplitter() : MachineFunctionPass(ID) {
+    initializeMachineFunctionSplitterPass(*PassRegistry::getPassRegistry());
+  }
+
+  StringRef getPassName() const override {
+    return "Machine Function Splitter Transformation";
+  }
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override;
+
+  bool runOnMachineFunction(MachineFunction &F) override;
+};
+} // end anonymous namespace
+
+static bool isColdBlock(MachineBasicBlock &MBB,
+                        const MachineBlockFrequencyInfo *MBFI,
+                        ProfileSummaryInfo *PSI) {
+  Optional<uint64_t> Count = MBFI->getBlockProfileCount(&MBB);
+  if (!Count.hasValue())
+    return true;
+
+  if (PercentileCutoff > 0) {
+    return PSI->isColdCountNthPercentile(PercentileCutoff, *Count);
+  }
+  return (*Count < ColdCountThreshold);
+}
+
+bool MachineFunctionSplitter::runOnMachineFunction(MachineFunction &MF) {
+  // TODO: We only target functions with profile data. Static information may
+  // also be considered but we don't see performance improvements yet.
+  if (!MF.getFunction().hasProfileData())
+    return false;
+
+  // TODO: We don't split functions where a section attribute has been set
+  // since the split part may not be placed in a contiguous region. It may also
+  // be more beneficial to augment the linker to ensure contiguous layout of
+  // split functions within the same section as specified by the attribute.
+  if (!MF.getFunction().getSection().empty())
+    return false;
+
+  // We don't want to proceed further for cold functions
+  // or functions of unknown hotness. Lukewarm functions have no prefix.
+  Optional<StringRef> SectionPrefix = MF.getFunction().getSectionPrefix();
+  if (SectionPrefix.hasValue() &&
+      (SectionPrefix.getValue().equals(".unlikely") ||
+       SectionPrefix.getValue().equals(".unknown"))) {
+    return false;
+  }
+
+  // Renumbering blocks here preserves the order of the blocks as
+  // sortBasicBlocksAndUpdateBranches uses the numeric identifier to sort
+  // blocks. Preserving the order of blocks is essential to retaining decisions
+  // made by prior passes such as MachineBlockPlacement.
+  MF.RenumberBlocks();
+  MF.setBBSectionsType(BasicBlockSection::Preset);
+  auto *MBFI = &getAnalysis<MachineBlockFrequencyInfo>();
+  auto *PSI = &getAnalysis<ProfileSummaryInfoWrapperPass>().getPSI();
+
+  for (auto &MBB : MF) {
+    // FIXME: We retain the entry block and conservatively keep all landing pad
+    // blocks as part of the original function. Once D73739 is submitted, we can
+    // improve the handling of ehpads.
+    if ((MBB.pred_empty() || MBB.isEHPad()))
+      continue;
+    if (isColdBlock(MBB, MBFI, PSI))
+      MBB.setSectionID(MBBSectionID::ColdSectionID);
+  }
+
+  auto Comparator = [](const MachineBasicBlock &X, const MachineBasicBlock &Y) {
+    return X.getSectionID().Type < Y.getSectionID().Type;
+  };
+  llvm::sortBasicBlocksAndUpdateBranches(MF, Comparator);
+
+  return true;
+}
+
+void MachineFunctionSplitter::getAnalysisUsage(AnalysisUsage &AU) const {
+  AU.addRequired<MachineModuleInfoWrapperPass>();
+  AU.addRequired<MachineBlockFrequencyInfo>();
+  AU.addRequired<ProfileSummaryInfoWrapperPass>();
+}
+
+char MachineFunctionSplitter::ID = 0;
+INITIALIZE_PASS(MachineFunctionSplitter, "machine-function-splitter",
+                "Split machine functions using profile information", false,
+                false)
+
+MachineFunctionPass *llvm::createMachineFunctionSplitterPass() {
+  return new MachineFunctionSplitter();
+}