diff --git a/llvm/lib/CodeGen/SelectOptimize.cpp b/llvm/lib/CodeGen/SelectOptimize.cpp
--- a/llvm/lib/CodeGen/SelectOptimize.cpp
+++ b/llvm/lib/CodeGen/SelectOptimize.cpp
@@ -10,34 +10,364 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/BlockFrequencyInfo.h"
+#include "llvm/Analysis/BranchProbabilityInfo.h"
+#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/OptimizationRemarkEmitter.h"
+#include "llvm/Analysis/ProfileSummaryInfo.h"
+#include "llvm/Analysis/TargetTransformInfo.h"
 #include "llvm/CodeGen/Passes.h"
+#include "llvm/CodeGen/TargetLowering.h"
+#include "llvm/CodeGen/TargetPassConfig.h"
+#include "llvm/CodeGen/TargetSchedule.h"
+#include "llvm/CodeGen/TargetSubtargetInfo.h"
+#include "llvm/IR/BasicBlock.h"
+#include "llvm/IR/Dominators.h"
 #include "llvm/IR/Function.h"
+#include "llvm/IR/Instruction.h"
 #include "llvm/InitializePasses.h"
 #include "llvm/Pass.h"
+#include "llvm/Target/TargetMachine.h"
+#include "llvm/Transforms/Utils/SizeOpts.h"
+#include <algorithm>
+#include <memory>
+#include <queue>
+#include <stack>
+#include <string>
 
 using namespace llvm;
 
+#define DEBUG_TYPE "select-optimize"
+
+STATISTIC(NumSelectOptAnalyzed,
+          "Number of select groups considered for conversion to branch");
+STATISTIC(NumSelectConvertedExpColdOperand,
+          "Number of select groups converted due to expensive cold operand");
+STATISTIC(NumSelectConvertedHighPred,
+          "Number of select groups converted due to high-predictability");
+STATISTIC(NumSelectUnPred,
+          "Number of select groups not converted due to unpredictability");
+
+static cl::opt<unsigned> ColdOperandThreshold(
+    "cold-operand-threshold",
+    cl::desc("Maximum frequency of path for an operand to be considered cold."),
+    cl::init(20), cl::Hidden);
+
 namespace {
 
 class SelectOptimize : public FunctionPass {
+  const TargetMachine *TM = nullptr;
+  const TargetSubtargetInfo *TSI;
+  const TargetLowering *TLI = nullptr;
+  const TargetTransformInfo *TTI = nullptr;
+  const LoopInfo *LI;
+  DominatorTree *DT;
+  std::unique_ptr<BlockFrequencyInfo> BFI;
+  std::unique_ptr<BranchProbabilityInfo> BPI;
+  ProfileSummaryInfo *PSI;
+  OptimizationRemarkEmitter *ORE;
+
 public:
   static char ID;
+
   SelectOptimize() : FunctionPass(ID) {
     initializeSelectOptimizePass(*PassRegistry::getPassRegistry());
   }
 
   bool runOnFunction(Function &F) override;
 
-  void getAnalysisUsage(AnalysisUsage &AU) const override {}
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.addRequired<ProfileSummaryInfoWrapperPass>();
+    AU.addRequired<TargetPassConfig>();
+    AU.addRequired<TargetTransformInfoWrapperPass>();
+    AU.addRequired<DominatorTreeWrapperPass>();
+    AU.addRequired<LoopInfoWrapperPass>();
+    AU.addRequired<OptimizationRemarkEmitterWrapperPass>();
+  }
+
+private:
+  // Select groups consist of consecutive select instructions with the same
+  // condition.
+  using SelectGroup = SmallVector<SelectInst *, 2>;
+  using SelectGroups = SmallVector<SelectGroup, 2>;
+
+  bool optimizeSelects(Function &F);
+  void optimizeSelectsBase(Function &F, SelectGroups &ProfSIGroups);
+  void optimizeSelectsInnerLoops(Function &F, SelectGroups &ProfSIGroups);
+  void convertProfitableSIGroups(SelectGroups &ProfSIGroups);
+  void collectSelectGroups(BasicBlock &BB, SelectGroups &SIGroups);
+  void findProfitableSIGroupsBase(SelectGroups &SIGroups,
+                                  SelectGroups &ProfSIGroups);
+  bool isConvertToBranchProfitableBase(const SmallVector<SelectInst *, 2> &ASI);
+  bool hasExpensiveColdOperand(const SmallVector<SelectInst *, 2> &ASI);
+  void getOneUseChain(Instruction *I, SmallVector<Instruction *, 2> &Chain);
+  bool isSelectHighlyPredictable(SelectInst *SI);
+  bool isExpensiveInst(Instruction *I);
+  bool isSelectKindSupported(SelectInst *SI);
 };
 } // namespace
 
 char SelectOptimize::ID = 0;
-INITIALIZE_PASS(SelectOptimize, "select-optimize", "Optimize selects", false,
-                false)
+
+INITIALIZE_PASS_BEGIN(SelectOptimize, DEBUG_TYPE, "Optimize selects", false,
+                      false)
+INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(ProfileSummaryInfoWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(TargetPassConfig)
+INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(OptimizationRemarkEmitterWrapperPass)
+INITIALIZE_PASS_END(SelectOptimize, DEBUG_TYPE, "Optimize selects", false,
+                    false)
 
 FunctionPass *llvm::createSelectOptimizePass() { return new SelectOptimize(); }
 
 bool SelectOptimize::runOnFunction(Function &F) {
+  TM = &getAnalysis<TargetPassConfig>().getTM<TargetMachine>();
+  TSI = TM->getSubtargetImpl(F);
+  TLI = TSI->getTargetLowering();
+
+  // If none of the select types is supported then skip this pass.
+  // This is an optimization pass. Legality issues will be handled by
+  // instruction selection.
+  if (!TLI->isSelectSupported(TargetLowering::ScalarValSelect) &&
+      !TLI->isSelectSupported(TargetLowering::ScalarCondVectorVal) &&
+      !TLI->isSelectSupported(TargetLowering::VectorMaskSelect))
+    return false;
+
+  // If even a predictable select is cheap, then a branch cannot be cheaper.
+  if (!TLI->isPredictableSelectExpensive())
+    return false;
+
+  TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
+  DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
+  LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
+  BPI.reset(new BranchProbabilityInfo(F, *LI));
+  BFI.reset(new BlockFrequencyInfo(F, *BPI, *LI));
+  PSI = &getAnalysis<ProfileSummaryInfoWrapperPass>().getPSI();
+  ORE = &getAnalysis<OptimizationRemarkEmitterWrapperPass>().getORE();
+
+  // When optimizing for size, selects are preferable over branches.
+  if (F.hasOptSize() || llvm::shouldOptimizeForSize(&F, PSI, BFI.get()))
+    return false;
+
+  return optimizeSelects(F);
+}
+
+bool SelectOptimize::optimizeSelects(Function &F) {
+  // Determine for which select groups it is profitable converting to branches.
+  SelectGroups ProfSIGroups;
+  // Base heuristics apply only to non-loops and outer loops.
+  optimizeSelectsBase(F, ProfSIGroups);
+  // Separate heuristics for inner-most loops.
+  optimizeSelectsInnerLoops(F, ProfSIGroups);
+
+  // Convert to branches the select groups that were deemed
+  // profitable-to-convert.
+  convertProfitableSIGroups(ProfSIGroups);
+
+  // Code modified if at least one select group was converted.
+  return !ProfSIGroups.empty();
+}
+
+void SelectOptimize::optimizeSelectsBase(Function &F,
+                                         SelectGroups &ProfSIGroups) {
+  // Collect all the select groups.
+  SelectGroups SIGroups;
+  for (BasicBlock &BB : F) {
+    // Base heuristics apply only to non-loops and outer loops.
+    Loop *L = LI->getLoopFor(&BB);
+    if (L && L->isInnermost())
+      continue;
+    collectSelectGroups(BB, SIGroups);
+  }
+
+  // Determine for which select groups it is profitable converting to branches.
+  findProfitableSIGroupsBase(SIGroups, ProfSIGroups);
+}
+
+void SelectOptimize::optimizeSelectsInnerLoops(Function &F,
+                                               SelectGroups &ProfSIGroups) {
   llvm_unreachable("Unimplemented");
 }
+
+void SelectOptimize::convertProfitableSIGroups(SelectGroups &ProfSIGroups) {
+  llvm_unreachable("Unimplemented");
+}
+
+void SelectOptimize::collectSelectGroups(BasicBlock &BB,
+                                         SelectGroups &SIGroups) {
+  BasicBlock::iterator BBIt = BB.begin();
+  while (BBIt != BB.end()) {
+    Instruction *I = &*BBIt++;
+    if (SelectInst *SI = dyn_cast<SelectInst>(I)) {
+      SelectGroup SIGroup;
+      SIGroup.push_back(SI);
+      while (BBIt != BB.end()) {
+        SelectInst *NI = dyn_cast<SelectInst>(&*BBIt);
+        if (NI && SI->getCondition() == NI->getCondition()) {
+          SIGroup.push_back(NI);
+          ++BBIt;
+        } else {
+          break;
+        }
+      }
+
+      // If the select type is not supported, no point optimizing it.
+      // Instruction selection will take care of it.
+      if (!isSelectKindSupported(SI))
+        continue;
+
+      SIGroups.push_back(SIGroup);
+    }
+  }
+}
+
+void SelectOptimize::findProfitableSIGroupsBase(SelectGroups &SIGroups,
+                                                SelectGroups &ProfSIGroups) {
+  for (SelectGroup &ASI : SIGroups) {
+    ++NumSelectOptAnalyzed;
+    if (isConvertToBranchProfitableBase(ASI))
+      ProfSIGroups.push_back(ASI);
+  }
+}
+
+bool SelectOptimize::isConvertToBranchProfitableBase(
+    const SmallVector<SelectInst *, 2> &ASI) {
+  SelectInst *SI = ASI.front();
+  OptimizationRemark OR(DEBUG_TYPE, "SelectOpti", SI);
+  OptimizationRemarkMissed ORmiss(DEBUG_TYPE, "SelectOpti", SI);
+
+  // If unpredictable, branch form is more profitable.
+  if (SI->getMetadata(LLVMContext::MD_unpredictable)) {
+    ++NumSelectUnPred;
+    ORmiss << "Not converted to branch because of unpredictable branch. ";
+    ORE->emit(ORmiss);
+    return false;
+  }
+
+  // If highly predictable, branch form is more profitable.
+  if (isSelectHighlyPredictable(SI)) {
+    ++NumSelectConvertedHighPred;
+    OR << "Converted to branch because of highly predictable branch. ";
+    ORE->emit(OR);
+    return true;
+  }
+
+  // Look for expensive operands in the cold operand's (if any) dependence
+  // chain of any of the selects in the group.
+  if (hasExpensiveColdOperand(ASI)) {
+    ++NumSelectConvertedExpColdOperand;
+    OR << "Converted to branch because of expensive cold operand.";
+    ORE->emit(OR);
+    return true;
+  }
+
+  ORmiss << "Not profitable to convert to branch (base heuristic).";
+  ORE->emit(ORmiss);
+  return false;
+}
+
+bool SelectOptimize::hasExpensiveColdOperand(
+    const SmallVector<SelectInst *, 2> &ASI) {
+  bool ColdOperand = false;
+  uint64_t TrueWeight, FalseWeight;
+  if (ASI.front()->extractProfMetadata(TrueWeight, FalseWeight)) {
+    uint64_t Min = std::min(TrueWeight, FalseWeight);
+    uint64_t Sum = TrueWeight + FalseWeight;
+    // Is there a path with frequency <ColdOperandThreshold% (default:20%) ?
+    ColdOperand = Sum * ColdOperandThreshold > 100 * Min;
+  }
+  if (!ColdOperand)
+    return false;
+  // Check if the cold path's dependence chain has an expensive operation for
+  // any of the selects of the group.
+  for (SelectInst *SI : ASI) {
+    Instruction *ColdI = nullptr;
+    if (TrueWeight < FalseWeight)
+      ColdI = dyn_cast<Instruction>(SI->getTrueValue());
+    else
+      ColdI = dyn_cast<Instruction>(SI->getFalseValue());
+    if (ColdI && ColdI->hasOneUse()) {
+      SmallVector<Instruction *, 2> ColdChain;
+      getOneUseChain(ColdI, ColdChain);
+      for (auto *ColdII : ColdChain)
+        if (isExpensiveInst(ColdII))
+          return true;
+    }
+  }
+  return false;
+}
+
+void SelectOptimize::getOneUseChain(Instruction *I,
+                                    SmallVector<Instruction *, 2> &Chain) {
+  std::queue<Instruction *> Worklist;
+  Worklist.push(I);
+  SmallPtrSet<Instruction *, 2> Visited;
+  const Loop *L = LI->getLoopFor(I->getParent());
+  while (!Worklist.empty()) {
+    Instruction *II = Worklist.front();
+    Worklist.pop();
+
+    if (Visited.count(II))
+      continue;
+    Visited.insert(II);
+
+    if (I != II && !II->hasOneUse())
+      continue;
+
+    // Avoid considering instructions in outer or independent loops, or non-loop
+    // instructions (instructions with potentially much less frequency than the
+    // operand of the select).
+    const Loop *LII = LI->getLoopFor(II->getParent());
+    if (L && L != LII && (!LII || !L->contains(LII)))
+      continue;
+
+    // Avoid phi nodes that are not part of a loop-carried dependence.
+    // Could source from a cold basic block.
+    if (isa<PHINode>(II)) {
+      if (!LII)
+        continue;
+      if (LII->getHeader() != II->getParent())
+        continue;
+    }
+
+    Chain.push_back(II);
+    for (unsigned k = 0; k < II->getNumOperands(); ++k)
+      if (auto *OpI = dyn_cast<Instruction>(II->getOperand(k)))
+        Worklist.push(OpI);
+  }
+}
+
+bool SelectOptimize::isSelectHighlyPredictable(SelectInst *SI) {
+  uint64_t TrueWeight, FalseWeight;
+  if (SI->extractProfMetadata(TrueWeight, FalseWeight)) {
+    uint64_t Max = std::max(TrueWeight, FalseWeight);
+    uint64_t Sum = TrueWeight + FalseWeight;
+    if (Sum != 0) {
+      auto Probability = BranchProbability::getBranchProbability(Max, Sum);
+      if (Probability > TTI->getPredictableBranchThreshold())
+        return true;
+    }
+  }
+  return false;
+}
+
+bool SelectOptimize::isExpensiveInst(Instruction *I) {
+  return TTI->getInstructionCost(I, TargetTransformInfo::TCK_Latency) >=
+         TargetTransformInfo::TCC_Expensive;
+}
+
+bool SelectOptimize::isSelectKindSupported(SelectInst *SI) {
+  bool VectorCond = !SI->getCondition()->getType()->isIntegerTy(1);
+  TargetLowering::SelectSupportKind SelectKind;
+  if (VectorCond)
+    SelectKind = TargetLowering::VectorMaskSelect;
+  else if (SI->getType()->isVectorTy())
+    SelectKind = TargetLowering::ScalarCondVectorVal;
+  else
+    SelectKind = TargetLowering::ScalarValSelect;
+  return TLI->isSelectSupported(SelectKind);
+}