1 files changed, 285 insertions, 170 deletions
diff --git a/contrib/llvm/lib/Transforms/Scalar/LoopUnswitch.cpp b/contrib/llvm/lib/Transforms/Scalar/LoopUnswitch.cpp
index cbc563b..95d7f8a 100644
--- a/contrib/llvm/lib/Transforms/Scalar/LoopUnswitch.cpp
+++ b/contrib/llvm/lib/Transforms/Scalar/LoopUnswitch.cpp
@@ -30,6 +30,7 @@
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/GlobalsModRef.h"
 #include "llvm/Analysis/AssumptionCache.h"
 #include "llvm/Analysis/CodeMetrics.h"
 #include "llvm/Analysis/InstructionSimplify.h"
@@ -37,6 +38,10 @@
 #include "llvm/Analysis/LoopPass.h"
 #include "llvm/Analysis/ScalarEvolution.h"
 #include "llvm/Analysis/TargetTransformInfo.h"
+#include "llvm/Analysis/BlockFrequencyInfoImpl.h"
+#include "llvm/Analysis/BlockFrequencyInfo.h"
+#include "llvm/Analysis/BranchProbabilityInfo.h"
+#include "llvm/Support/BranchProbability.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/Dominators.h"
@@ -70,6 +75,19 @@ static cl::opt<unsigned>
 Threshold("loop-unswitch-threshold", cl::desc("Max loop size to unswitch"),
           cl::init(100), cl::Hidden);
 
+static cl::opt<bool>
+LoopUnswitchWithBlockFrequency("loop-unswitch-with-block-frequency",
+    cl::init(false), cl::Hidden,
+    cl::desc("Enable the use of the block frequency analysis to access PGO "
+             "heuristics to minimize code growth in cold regions."));
+
+static cl::opt<unsigned>
+ColdnessThreshold("loop-unswitch-coldness-threshold", cl::init(1), cl::Hidden,
+    cl::desc("Coldness threshold in percentage. The loop header frequency "
+             "(relative to the entry frequency) is compared with this "
+             "threshold to determine if non-trivial unswitching should be "
+             "enabled."));
+
 namespace {
 
   class LUAnalysisCache {
@@ -148,12 +166,19 @@ namespace {
     LPPassManager *LPM;
     AssumptionCache *AC;
 
-    // LoopProcessWorklist - Used to check if second loop needs processing
-    // after RewriteLoopBodyWithConditionConstant rewrites first loop.
+    // Used to check if second loop needs processing after
+    // RewriteLoopBodyWithConditionConstant rewrites first loop.
     std::vector<Loop*> LoopProcessWorklist;
 
     LUAnalysisCache BranchesInfo;
 
+    bool EnabledPGO;
+
+    // BFI and ColdEntryFreq are only used when PGO and
+    // LoopUnswitchWithBlockFrequency are enabled.
+    BlockFrequencyInfo BFI;
+    BlockFrequency ColdEntryFreq;
+
     bool OptimizeForSize;
     bool redoLoop;
 
@@ -192,9 +217,11 @@ namespace {
       AU.addPreserved<LoopInfoWrapperPass>();
       AU.addRequiredID(LCSSAID);
       AU.addPreservedID(LCSSAID);
+      AU.addRequired<DominatorTreeWrapperPass>();
       AU.addPreserved<DominatorTreeWrapperPass>();
-      AU.addPreserved<ScalarEvolution>();
+      AU.addPreserved<ScalarEvolutionWrapperPass>();
       AU.addRequired<TargetTransformInfoWrapperPass>();
+      AU.addPreserved<GlobalsAAWrapperPass>();
     }
 
   private:
@@ -210,7 +237,10 @@ namespace {
 
     /// Split all of the edges from inside the loop to their exit blocks.
     /// Update the appropriate Phi nodes as we do so.
-    void SplitExitEdges(Loop *L, const SmallVectorImpl<BasicBlock *> &ExitBlocks);
+    void SplitExitEdges(Loop *L,
+                        const SmallVectorImpl<BasicBlock *> &ExitBlocks);
+
+    bool TryTrivialLoopUnswitch(bool &Changed);
 
     bool UnswitchIfProfitable(Value *LoopCond, Constant *Val,
                               TerminatorInst *TI = nullptr);
@@ -229,9 +259,6 @@ namespace {
                                         TerminatorInst *TI);
 
     void SimplifyCode(std::vector<Instruction*> &Worklist, Loop *L);
-    bool IsTrivialUnswitchCondition(Value *Cond, Constant **Val = nullptr,
-                                    BasicBlock **LoopExit = nullptr);
-
   };
 }
 
@@ -367,9 +394,8 @@ Pass *llvm::createLoopUnswitchPass(bool Os) {
   return new LoopUnswitch(Os);
 }
 
-/// FindLIVLoopCondition - Cond is a condition that occurs in L.  If it is
-/// invariant in the loop, or has an invariant piece, return the invariant.
-/// Otherwise, return null.
+/// Cond is a condition that occurs in L. If it is invariant in the loop, or has
+/// an invariant piece, return the invariant. Otherwise, return null.
 static Value *FindLIVLoopCondition(Value *Cond, Loop *L, bool &Changed) {
 
   // We started analyze new instruction, increment scanned instructions counter.
@@ -411,11 +437,23 @@ bool LoopUnswitch::runOnLoop(Loop *L, LPPassManager &LPM_Ref) {
       *L->getHeader()->getParent());
   LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
   LPM = &LPM_Ref;
-  DominatorTreeWrapperPass *DTWP =
-      getAnalysisIfAvailable<DominatorTreeWrapperPass>();
-  DT = DTWP ? &DTWP->getDomTree() : nullptr;
+  DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
   currentLoop = L;
   Function *F = currentLoop->getHeader()->getParent();
+
+  EnabledPGO = F->getEntryCount().hasValue();
+
+  if (LoopUnswitchWithBlockFrequency && EnabledPGO) {
+    BranchProbabilityInfo BPI(*F, *LI);
+    BFI.calculate(*L->getHeader()->getParent(), BPI, *LI);
+
+    // Use BranchProbability to compute a minimum frequency based on
+    // function entry baseline frequency. Loops with headers below this
+    // frequency are considered as cold.
+    const BranchProbability ColdProb(ColdnessThreshold, 100);
+    ColdEntryFreq = BlockFrequency(BFI.getEntryFreq()) * ColdProb;
+  }
+
   bool Changed = false;
   do {
     assert(currentLoop->isLCSSAForm(*DT));
@@ -423,16 +461,13 @@ bool LoopUnswitch::runOnLoop(Loop *L, LPPassManager &LPM_Ref) {
     Changed |= processCurrentLoop();
   } while(redoLoop);
 
-  if (Changed) {
-    // FIXME: Reconstruct dom info, because it is not preserved properly.
-    if (DT)
-      DT->recalculate(*F);
-  }
+  // FIXME: Reconstruct dom info, because it is not preserved properly.
+  if (Changed)
+    DT->recalculate(*F);
   return Changed;
 }
 
-/// processCurrentLoop - Do actual work and unswitch loop if possible
-/// and profitable.
+/// Do actual work and unswitch loop if possible and profitable.
 bool LoopUnswitch::processCurrentLoop() {
   bool Changed = false;
 
@@ -452,14 +487,48 @@ bool LoopUnswitch::processCurrentLoop() {
 
   LLVMContext &Context = loopHeader->getContext();
 
-  // Probably we reach the quota of branches for this loop. If so
-  // stop unswitching.
+  // Analyze loop cost, and stop unswitching if loop content can not be duplicated.
   if (!BranchesInfo.countLoop(
           currentLoop, getAnalysis<TargetTransformInfoWrapperPass>().getTTI(
                            *currentLoop->getHeader()->getParent()),
           AC))
     return false;
 
+  // Try trivial unswitch first before loop over other basic blocks in the loop.
+  if (TryTrivialLoopUnswitch(Changed)) {
+    return true;
+  }
+
+  // Do not unswitch loops containing convergent operations, as we might be
+  // making them control dependent on the unswitch value when they were not
+  // before.
+  // FIXME: This could be refined to only bail if the convergent operation is
+  // not already control-dependent on the unswitch value.
+  for (const auto BB : currentLoop->blocks()) {
+    for (auto &I : *BB) {
+      auto CS = CallSite(&I);
+      if (!CS) continue;
+      if (CS.hasFnAttr(Attribute::Convergent))
+        return false;
+    }
+  }
+
+  // Do not do non-trivial unswitch while optimizing for size.
+  // FIXME: Use Function::optForSize().
+  if (OptimizeForSize ||
+      loopHeader->getParent()->hasFnAttribute(Attribute::OptimizeForSize))
+    return false;
+
+  if (LoopUnswitchWithBlockFrequency && EnabledPGO) {
+    // Compute the weighted frequency of the hottest block in the
+    // loop (loopHeader in this case since inner loops should be
+    // processed before outer loop). If it is less than ColdFrequency,
+    // we should not unswitch.
+    BlockFrequency LoopEntryFreq = BFI.getBlockFreq(loopHeader);
+    if (LoopEntryFreq < ColdEntryFreq)
+      return false;
+  }
+
   // Loop over all of the basic blocks in the loop.  If we find an interior
   // block that is branching on a loop-invariant condition, we can unswitch this
   // loop.
@@ -528,8 +597,8 @@ bool LoopUnswitch::processCurrentLoop() {
   return Changed;
 }
 
-/// isTrivialLoopExitBlock - Check to see if all paths from BB exit the
-/// loop with no side effects (including infinite loops).
+/// Check to see if all paths from BB exit the loop with no side effects
+/// (including infinite loops).
 ///
 /// If true, we return true and set ExitBB to the block we
 /// exit through.
@@ -566,9 +635,9 @@ static bool isTrivialLoopExitBlockHelper(Loop *L, BasicBlock *BB,
   return true;
 }
 
-/// isTrivialLoopExitBlock - Return true if the specified block unconditionally
-/// leads to an exit from the specified loop, and has no side-effects in the
-/// process.  If so, return the block that is exited to, otherwise return null.
+/// Return true if the specified block unconditionally leads to an exit from
+/// the specified loop, and has no side-effects in the process. If so, return
+/// the block that is exited to, otherwise return null.
 static BasicBlock *isTrivialLoopExitBlock(Loop *L, BasicBlock *BB) {
   std::set<BasicBlock*> Visited;
   Visited.insert(L->getHeader());  // Branches to header make infinite loops.
@@ -578,105 +647,11 @@ static BasicBlock *isTrivialLoopExitBlock(Loop *L, BasicBlock *BB) {
   return nullptr;
 }
 
-/// IsTrivialUnswitchCondition - Check to see if this unswitch condition is
-/// trivial: that is, that the condition controls whether or not the loop does
-/// anything at all.  If this is a trivial condition, unswitching produces no
-/// code duplications (equivalently, it produces a simpler loop and a new empty
-/// loop, which gets deleted).
-///
-/// If this is a trivial condition, return true, otherwise return false.  When
-/// returning true, this sets Cond and Val to the condition that controls the
-/// trivial condition: when Cond dynamically equals Val, the loop is known to
-/// exit.  Finally, this sets LoopExit to the BB that the loop exits to when
-/// Cond == Val.
-///
-bool LoopUnswitch::IsTrivialUnswitchCondition(Value *Cond, Constant **Val,
-                                       BasicBlock **LoopExit) {
-  BasicBlock *Header = currentLoop->getHeader();
-  TerminatorInst *HeaderTerm = Header->getTerminator();
-  LLVMContext &Context = Header->getContext();
-
-  BasicBlock *LoopExitBB = nullptr;
-  if (BranchInst *BI = dyn_cast<BranchInst>(HeaderTerm)) {
-    // If the header block doesn't end with a conditional branch on Cond, we
-    // can't handle it.
-    if (!BI->isConditional() || BI->getCondition() != Cond)
-      return false;
-
-    // Check to see if a successor of the branch is guaranteed to
-    // exit through a unique exit block without having any
-    // side-effects.  If so, determine the value of Cond that causes it to do
-    // this.
-    if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop,
-                                             BI->getSuccessor(0)))) {
-      if (Val) *Val = ConstantInt::getTrue(Context);
-    } else if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop,
-                                                    BI->getSuccessor(1)))) {
-      if (Val) *Val = ConstantInt::getFalse(Context);
-    }
-  } else if (SwitchInst *SI = dyn_cast<SwitchInst>(HeaderTerm)) {
-    // If this isn't a switch on Cond, we can't handle it.
-    if (SI->getCondition() != Cond) return false;
-
-    // Check to see if a successor of the switch is guaranteed to go to the
-    // latch block or exit through a one exit block without having any
-    // side-effects.  If so, determine the value of Cond that causes it to do
-    // this.
-    // Note that we can't trivially unswitch on the default case or
-    // on already unswitched cases.
-    for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
-         i != e; ++i) {
-      BasicBlock *LoopExitCandidate;
-      if ((LoopExitCandidate = isTrivialLoopExitBlock(currentLoop,
-                                               i.getCaseSuccessor()))) {
-        // Okay, we found a trivial case, remember the value that is trivial.
-        ConstantInt *CaseVal = i.getCaseValue();
-
-        // Check that it was not unswitched before, since already unswitched
-        // trivial vals are looks trivial too.
-        if (BranchesInfo.isUnswitched(SI, CaseVal))
-          continue;
-        LoopExitBB = LoopExitCandidate;
-        if (Val) *Val = CaseVal;
-        break;
-      }
-    }
-  }
-
-  // If we didn't find a single unique LoopExit block, or if the loop exit block
-  // contains phi nodes, this isn't trivial.
-  if (!LoopExitBB || isa<PHINode>(LoopExitBB->begin()))
-    return false;   // Can't handle this.
-
-  if (LoopExit) *LoopExit = LoopExitBB;
-
-  // We already know that nothing uses any scalar values defined inside of this
-  // loop.  As such, we just have to check to see if this loop will execute any
-  // side-effecting instructions (e.g. stores, calls, volatile loads) in the
-  // part of the loop that the code *would* execute.  We already checked the
-  // tail, check the header now.
-  for (BasicBlock::iterator I = Header->begin(), E = Header->end(); I != E; ++I)
-    if (I->mayHaveSideEffects())
-      return false;
-  return true;
-}
-
-/// UnswitchIfProfitable - We have found that we can unswitch currentLoop when
-/// LoopCond == Val to simplify the loop.  If we decide that this is profitable,
+/// We have found that we can unswitch currentLoop when LoopCond == Val to
+/// simplify the loop.  If we decide that this is profitable,
 /// unswitch the loop, reprocess the pieces, then return true.
 bool LoopUnswitch::UnswitchIfProfitable(Value *LoopCond, Constant *Val,
                                         TerminatorInst *TI) {
-  Function *F = loopHeader->getParent();
-  Constant *CondVal = nullptr;
-  BasicBlock *ExitBlock = nullptr;
-
-  if (IsTrivialUnswitchCondition(LoopCond, &CondVal, &ExitBlock)) {
-    // If the condition is trivial, always unswitch. There is no code growth
-    // for this case.
-    UnswitchTrivialCondition(currentLoop, LoopCond, CondVal, ExitBlock, TI);
-    return true;
-  }
-
   // Check to see if it would be profitable to unswitch current loop.
   if (!BranchesInfo.CostAllowsUnswitching()) {
     DEBUG(dbgs() << "NOT unswitching loop %"
@@ -687,32 +662,27 @@ bool LoopUnswitch::UnswitchIfProfitable(Value *LoopCond, Constant *Val,
     return false;
   }
 
-  // Do not do non-trivial unswitch while optimizing for size.
-  if (OptimizeForSize || F->hasFnAttribute(Attribute::OptimizeForSize))
-    return false;
-
   UnswitchNontrivialCondition(LoopCond, Val, currentLoop, TI);
   return true;
 }
 
-/// CloneLoop - Recursively clone the specified loop and all of its children,
+/// Recursively clone the specified loop and all of its children,
 /// mapping the blocks with the specified map.
 static Loop *CloneLoop(Loop *L, Loop *PL, ValueToValueMapTy &VM,
                        LoopInfo *LI, LPPassManager *LPM) {
-  Loop *New = new Loop();
-  LPM->insertLoop(New, PL);
+  Loop &New = LPM->addLoop(PL);
 
   // Add all of the blocks in L to the new loop.
   for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
        I != E; ++I)
     if (LI->getLoopFor(*I) == L)
-      New->addBasicBlockToLoop(cast<BasicBlock>(VM[*I]), *LI);
+      New.addBasicBlockToLoop(cast<BasicBlock>(VM[*I]), *LI);
 
   // Add all of the subloops to the new loop.
   for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I)
-    CloneLoop(*I, New, VM, LI, LPM);
+    CloneLoop(*I, &New, VM, LI, LPM);
 
-  return New;
+  return &New;
 }
 
 static void copyMetadata(Instruction *DstInst, const Instruction *SrcInst,
@@ -744,15 +714,15 @@ static void copyMetadata(Instruction *DstInst, const Instruction *SrcInst,
         }
       }
       // fallthrough.
+    case LLVMContext::MD_make_implicit:
     case LLVMContext::MD_dbg:
       DstInst->setMetadata(MD.first, MD.second);
     }
   }
 }
 
-/// EmitPreheaderBranchOnCondition - Emit a conditional branch on two values
-/// if LIC == Val, branch to TrueDst, otherwise branch to FalseDest.  Insert the
-/// code immediately before InsertPt.
+/// Emit a conditional branch on two values if LIC == Val, branch to TrueDst,
+/// otherwise branch to FalseDest. Insert the code immediately before InsertPt.
 void LoopUnswitch::EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val,
                                                   BasicBlock *TrueDest,
                                                   BasicBlock *FalseDest,
@@ -782,11 +752,11 @@ void LoopUnswitch::EmitPreheaderBranchOnCondition(Value *LIC, Constant *Val,
   SplitCriticalEdge(BI, 1, Options);
 }
 
-/// UnswitchTrivialCondition - Given a loop that has a trivial unswitchable
-/// condition in it (a cond branch from its header block to its latch block,
-/// where the path through the loop that doesn't execute its body has no
-/// side-effects), unswitch it.  This doesn't involve any code duplication, just
-/// moving the conditional branch outside of the loop and updating loop info.
+/// Given a loop that has a trivial unswitchable condition in it (a cond branch
+/// from its header block to its latch block, where the path through the loop
+/// that doesn't execute its body has no side-effects), unswitch it. This
+/// doesn't involve any code duplication, just moving the conditional branch
+/// outside of the loop and updating loop info.
 void LoopUnswitch::UnswitchTrivialCondition(Loop *L, Value *Cond, Constant *Val,
                                             BasicBlock *ExitBlock,
                                             TerminatorInst *TI) {
@@ -810,7 +780,7 @@ void LoopUnswitch::UnswitchTrivialCondition(Loop *L, Value *Cond, Constant *Val,
   // without actually branching to it (the exit block should be dominated by the
   // loop header, not the preheader).
   assert(!L->contains(ExitBlock) && "Exit block is in the loop?");
-  BasicBlock *NewExit = SplitBlock(ExitBlock, ExitBlock->begin(), DT, LI);
+  BasicBlock *NewExit = SplitBlock(ExitBlock, &ExitBlock->front(), DT, LI);
 
   // Okay, now we have a position to branch from and a position to branch to,
   // insert the new conditional branch.
@@ -829,8 +799,155 @@ void LoopUnswitch::UnswitchTrivialCondition(Loop *L, Value *Cond, Constant *Val,
   ++NumTrivial;
 }
 
-/// SplitExitEdges - Split all of the edges from inside the loop to their exit
-/// blocks.  Update the appropriate Phi nodes as we do so.
+/// Check if the first non-constant condition starting from the loop header is
+/// a trivial unswitch condition: that is, a condition controls whether or not
+/// the loop does anything at all. If it is a trivial condition, unswitching
+/// produces no code duplications (equivalently, it produces a simpler loop and
+/// a new empty loop, which gets deleted). Therefore always unswitch trivial
+/// condition.
+bool LoopUnswitch::TryTrivialLoopUnswitch(bool &Changed) {
+  BasicBlock *CurrentBB = currentLoop->getHeader();
+  TerminatorInst *CurrentTerm = CurrentBB->getTerminator();
+  LLVMContext &Context = CurrentBB->getContext();
+
+  // If loop header has only one reachable successor (currently via an
+  // unconditional branch or constant foldable conditional branch, but
+  // should also consider adding constant foldable switch instruction in
+  // future), we should keep looking for trivial condition candidates in
+  // the successor as well. An alternative is to constant fold conditions
+  // and merge successors into loop header (then we only need to check header's
+  // terminator). The reason for not doing this in LoopUnswitch pass is that
+  // it could potentially break LoopPassManager's invariants. Folding dead
+  // branches could either eliminate the current loop or make other loops
+  // unreachable. LCSSA form might also not be preserved after deleting
+  // branches. The following code keeps traversing loop header's successors
+  // until it finds the trivial condition candidate (condition that is not a
+  // constant). Since unswitching generates branches with constant conditions,
+  // this scenario could be very common in practice.
+  SmallSet<BasicBlock*, 8> Visited;
+
+  while (true) {
+    // If we exit loop or reach a previous visited block, then
+    // we can not reach any trivial condition candidates (unfoldable
+    // branch instructions or switch instructions) and no unswitch
+    // can happen. Exit and return false.
+    if (!currentLoop->contains(CurrentBB) || !Visited.insert(CurrentBB).second)
+      return false;
+
+    // Check if this loop will execute any side-effecting instructions (e.g.
+    // stores, calls, volatile loads) in the part of the loop that the code
+    // *would* execute. Check the header first.
+    for (Instruction &I : *CurrentBB)
+      if (I.mayHaveSideEffects())
+        return false;
+
+    // FIXME: add check for constant foldable switch instructions.
+    if (BranchInst *BI = dyn_cast<BranchInst>(CurrentTerm)) {
+      if (BI->isUnconditional()) {
+        CurrentBB = BI->getSuccessor(0);
+      } else if (BI->getCondition() == ConstantInt::getTrue(Context)) {
+        CurrentBB = BI->getSuccessor(0);
+      } else if (BI->getCondition() == ConstantInt::getFalse(Context)) {
+        CurrentBB = BI->getSuccessor(1);
+      } else {
+        // Found a trivial condition candidate: non-foldable conditional branch.
+        break;
+      }
+    } else {
+      break;
+    }
+
+    CurrentTerm = CurrentBB->getTerminator();
+  }
+
+  // CondVal is the condition that controls the trivial condition.
+  // LoopExitBB is the BasicBlock that loop exits when meets trivial condition.
+  Constant *CondVal = nullptr;
+  BasicBlock *LoopExitBB = nullptr;
+
+  if (BranchInst *BI = dyn_cast<BranchInst>(CurrentTerm)) {
+    // If this isn't branching on an invariant condition, we can't unswitch it.
+    if (!BI->isConditional())
+      return false;
+
+    Value *LoopCond = FindLIVLoopCondition(BI->getCondition(),
+                                           currentLoop, Changed);
+
+    // Unswitch only if the trivial condition itself is an LIV (not
+    // partial LIV which could occur in and/or)
+    if (!LoopCond || LoopCond != BI->getCondition())
+      return false;
+
+    // Check to see if a successor of the branch is guaranteed to
+    // exit through a unique exit block without having any
+    // side-effects.  If so, determine the value of Cond that causes
+    // it to do this.
+    if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop,
+                                             BI->getSuccessor(0)))) {
+      CondVal = ConstantInt::getTrue(Context);
+    } else if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop,
+                                                    BI->getSuccessor(1)))) {
+      CondVal = ConstantInt::getFalse(Context);
+    }
+
+    // If we didn't find a single unique LoopExit block, or if the loop exit
+    // block contains phi nodes, this isn't trivial.
+    if (!LoopExitBB || isa<PHINode>(LoopExitBB->begin()))
+      return false;   // Can't handle this.
+
+    UnswitchTrivialCondition(currentLoop, LoopCond, CondVal, LoopExitBB,
+                             CurrentTerm);
+    ++NumBranches;
+    return true;
+  } else if (SwitchInst *SI = dyn_cast<SwitchInst>(CurrentTerm)) {
+    // If this isn't switching on an invariant condition, we can't unswitch it.
+    Value *LoopCond = FindLIVLoopCondition(SI->getCondition(),
+                                           currentLoop, Changed);
+
+    // Unswitch only if the trivial condition itself is an LIV (not
+    // partial LIV which could occur in and/or)
+    if (!LoopCond || LoopCond != SI->getCondition())
+      return false;
+
+    // Check to see if a successor of the switch is guaranteed to go to the
+    // latch block or exit through a one exit block without having any
+    // side-effects.  If so, determine the value of Cond that causes it to do
+    // this.
+    // Note that we can't trivially unswitch on the default case or
+    // on already unswitched cases.
+    for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
+         i != e; ++i) {
+      BasicBlock *LoopExitCandidate;
+      if ((LoopExitCandidate = isTrivialLoopExitBlock(currentLoop,
+                                               i.getCaseSuccessor()))) {
+        // Okay, we found a trivial case, remember the value that is trivial.
+        ConstantInt *CaseVal = i.getCaseValue();
+
+        // Check that it was not unswitched before, since already unswitched
+        // trivial vals are looks trivial too.
+        if (BranchesInfo.isUnswitched(SI, CaseVal))
+          continue;
+        LoopExitBB = LoopExitCandidate;
+        CondVal = CaseVal;
+        break;
+      }
+    }
+
+    // If we didn't find a single unique LoopExit block, or if the loop exit
+    // block contains phi nodes, this isn't trivial.
+    if (!LoopExitBB || isa<PHINode>(LoopExitBB->begin()))
+      return false;   // Can't handle this.
+
+    UnswitchTrivialCondition(currentLoop, LoopCond, CondVal, LoopExitBB,
+                             nullptr);
+    ++NumSwitches;
+    return true;
+  }
+  return false;
+}
+
+/// Split all of the edges from inside the loop to their exit blocks.
+/// Update the appropriate Phi nodes as we do so.
 void LoopUnswitch::SplitExitEdges(Loop *L,
                                const SmallVectorImpl<BasicBlock *> &ExitBlocks){
 
@@ -841,15 +958,14 @@ void LoopUnswitch::SplitExitEdges(Loop *L,
 
     // Although SplitBlockPredecessors doesn't preserve loop-simplify in
     // general, if we call it on all predecessors of all exits then it does.
-    SplitBlockPredecessors(ExitBlock, Preds, ".us-lcssa",
-                           /*AliasAnalysis*/ nullptr, DT, LI,
+    SplitBlockPredecessors(ExitBlock, Preds, ".us-lcssa", DT, LI,
                            /*PreserveLCSSA*/ true);
   }
 }
 
-/// UnswitchNontrivialCondition - We determined that the loop is profitable
-/// to unswitch when LIC equal Val.  Split it into loop versions and test the
-/// condition outside of either loop.  Return the loops created as Out1/Out2.
+/// We determined that the loop is profitable to unswitch when LIC equal Val.
+/// Split it into loop versions and test the condition outside of either loop.
+/// Return the loops created as Out1/Out2.
 void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val,
                                                Loop *L, TerminatorInst *TI) {
   Function *F = loopHeader->getParent();
@@ -858,8 +974,8 @@ void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val,
         << " blocks] in Function " << F->getName()
         << " when '" << *Val << "' == " << *LIC << "\n");
 
-  if (ScalarEvolution *SE = getAnalysisIfAvailable<ScalarEvolution>())
-    SE->forgetLoop(L);
+  if (auto *SEWP = getAnalysisIfAvailable<ScalarEvolutionWrapperPass>())
+    SEWP->getSE().forgetLoop(L);
 
   LoopBlocks.clear();
   NewBlocks.clear();
@@ -901,8 +1017,9 @@ void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val,
 
   // Splice the newly inserted blocks into the function right before the
   // original preheader.
-  F->getBasicBlockList().splice(NewPreheader, F->getBasicBlockList(),
-                                NewBlocks[0], F->end());
+  F->getBasicBlockList().splice(NewPreheader->getIterator(),
+                                F->getBasicBlockList(),
+                                NewBlocks[0]->getIterator(), F->end());
 
   // FIXME: We could register any cloned assumptions instead of clearing the
   // whole function's cache.
@@ -944,7 +1061,7 @@ void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val,
 
     if (LandingPadInst *LPad = NewExit->getLandingPadInst()) {
       PHINode *PN = PHINode::Create(LPad->getType(), 0, "",
-                                    ExitSucc->getFirstInsertionPt());
+                                    &*ExitSucc->getFirstInsertionPt());
 
       for (pred_iterator I = pred_begin(ExitSucc), E = pred_end(ExitSucc);
            I != E; ++I) {
@@ -960,7 +1077,8 @@ void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val,
   for (unsigned i = 0, e = NewBlocks.size(); i != e; ++i)
     for (BasicBlock::iterator I = NewBlocks[i]->begin(),
            E = NewBlocks[i]->end(); I != E; ++I)
-      RemapInstruction(I, VMap,RF_NoModuleLevelChanges|RF_IgnoreMissingEntries);
+      RemapInstruction(&*I, VMap,
+                       RF_NoModuleLevelChanges | RF_IgnoreMissingEntries);
 
   // Rewrite the original preheader to select between versions of the loop.
   BranchInst *OldBR = cast<BranchInst>(loopPreheader->getTerminator());
@@ -994,8 +1112,7 @@ void LoopUnswitch::UnswitchNontrivialCondition(Value *LIC, Constant *Val,
     RewriteLoopBodyWithConditionConstant(NewLoop, LICHandle, Val, true);
 }
 
-/// RemoveFromWorklist - Remove all instances of I from the worklist vector
-/// specified.
+/// Remove all instances of I from the worklist vector specified.
 static void RemoveFromWorklist(Instruction *I,
                                std::vector<Instruction*> &Worklist) {
 
@@ -1003,7 +1120,7 @@ static void RemoveFromWorklist(Instruction *I,
                  Worklist.end());
 }
 
-/// ReplaceUsesOfWith - When we find that I really equals V, remove I from the
+/// When we find that I really equals V, remove I from the
 /// program, replacing all uses with V and update the worklist.
 static void ReplaceUsesOfWith(Instruction *I, Value *V,
                               std::vector<Instruction*> &Worklist,
@@ -1025,9 +1142,9 @@ static void ReplaceUsesOfWith(Instruction *I, Value *V,
   ++NumSimplify;
 }
 
-// RewriteLoopBodyWithConditionConstant - We know either that the value LIC has
-// the value specified by Val in the specified loop, or we know it does NOT have
-// that value.  Rewrite any uses of LIC or of properties correlated to it.
+/// We know either that the value LIC has the value specified by Val in the
+/// specified loop, or we know it does NOT have that value.
+/// Rewrite any uses of LIC or of properties correlated to it.
 void LoopUnswitch::RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
                                                         Constant *Val,
                                                         bool IsEqual) {
@@ -1138,18 +1255,16 @@ void LoopUnswitch::RewriteLoopBodyWithConditionConstant(Loop *L, Value *LIC,
     // domtree here -- instead we force it to do a full recomputation
     // after the pass is complete -- but we do need to inform it of
     // new blocks.
-    if (DT)
-      DT->addNewBlock(Abort, NewSISucc);
+    DT->addNewBlock(Abort, NewSISucc);
   }
 
   SimplifyCode(Worklist, L);
 }
 
-/// SimplifyCode - Okay, now that we have simplified some instructions in the
-/// loop, walk over it and constant prop, dce, and fold control flow where
-/// possible.  Note that this is effectively a very simple loop-structure-aware
-/// optimizer.  During processing of this loop, L could very well be deleted, so
-/// it must not be used.
+/// Now that we have simplified some instructions in the loop, walk over it and
+/// constant prop, dce, and fold control flow where possible. Note that this is
+/// effectively a very simple loop-structure-aware optimizer. During processing
+/// of this loop, L could very well be deleted, so it must not be used.
 ///
 /// FIXME: When the loop optimizer is more mature, separate this out to a new
 /// pass.
@@ -1207,8 +1322,8 @@ void LoopUnswitch::SimplifyCode(std::vector<Instruction*> &Worklist, Loop *L) {
         Succ->replaceAllUsesWith(Pred);
 
         // Move all of the successor contents from Succ to Pred.
-        Pred->getInstList().splice(BI, Succ->getInstList(), Succ->begin(),
-                                   Succ->end());
+        Pred->getInstList().splice(BI->getIterator(), Succ->getInstList(),
+                                   Succ->begin(), Succ->end());
         LPM->deleteSimpleAnalysisValue(BI, L);
         BI->eraseFromParent();
         RemoveFromWorklist(BI, Worklist);