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diff --git a/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp b/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp
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index 0000000000000..e9671ee07e69c
--- /dev/null
+++ b/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp
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+//===-- WebAssemblyCFGStackify.cpp - CFG Stackification -------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// \brief This file implements a CFG stacking pass.
+///
+/// This pass reorders the blocks in a function to put them into a reverse
+/// post-order [0], with special care to keep the order as similar as possible
+/// to the original order, and to keep loops contiguous even in the case of
+/// split backedges.
+///
+/// Then, it inserts BLOCK and LOOP markers to mark the start of scopes, since
+/// scope boundaries serve as the labels for WebAssembly's control transfers.
+///
+/// This is sufficient to convert arbitrary CFGs into a form that works on
+/// WebAssembly, provided that all loops are single-entry.
+///
+/// [0] https://en.wikipedia.org/wiki/Depth-first_search#Vertex_orderings
+///
+//===----------------------------------------------------------------------===//
+
+#include "WebAssembly.h"
+#include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
+#include "WebAssemblySubtarget.h"
+#include "llvm/ADT/SCCIterator.h"
+#include "llvm/ADT/SetVector.h"
+#include "llvm/CodeGen/MachineDominators.h"
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/CodeGen/MachineInstrBuilder.h"
+#include "llvm/CodeGen/MachineLoopInfo.h"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+using namespace llvm;
+
+#define DEBUG_TYPE "wasm-cfg-stackify"
+
+namespace {
+class WebAssemblyCFGStackify final : public MachineFunctionPass {
+  const char *getPassName() const override {
+    return "WebAssembly CFG Stackify";
+  }
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.setPreservesCFG();
+    AU.addRequired<MachineDominatorTree>();
+    AU.addPreserved<MachineDominatorTree>();
+    AU.addRequired<MachineLoopInfo>();
+    AU.addPreserved<MachineLoopInfo>();
+    MachineFunctionPass::getAnalysisUsage(AU);
+  }
+
+  bool runOnMachineFunction(MachineFunction &MF) override;
+
+public:
+  static char ID; // Pass identification, replacement for typeid
+  WebAssemblyCFGStackify() : MachineFunctionPass(ID) {}
+};
+} // end anonymous namespace
+
+char WebAssemblyCFGStackify::ID = 0;
+FunctionPass *llvm::createWebAssemblyCFGStackify() {
+  return new WebAssemblyCFGStackify();
+}
+
+static void EliminateMultipleEntryLoops(MachineFunction &MF,
+                                        const MachineLoopInfo &MLI) {
+  SmallPtrSet<MachineBasicBlock *, 8> InSet;
+  for (scc_iterator<MachineFunction *> I = scc_begin(&MF), E = scc_end(&MF);
+       I != E; ++I) {
+    const std::vector<MachineBasicBlock *> &CurrentSCC = *I;
+
+    // Skip trivial SCCs.
+    if (CurrentSCC.size() == 1)
+      continue;
+
+    InSet.insert(CurrentSCC.begin(), CurrentSCC.end());
+    MachineBasicBlock *Header = nullptr;
+    for (MachineBasicBlock *MBB : CurrentSCC) {
+      for (MachineBasicBlock *Pred : MBB->predecessors()) {
+        if (InSet.count(Pred))
+          continue;
+        if (!Header) {
+          Header = MBB;
+          break;
+        }
+        // TODO: Implement multiple-entry loops.
+        report_fatal_error("multiple-entry loops are not supported yet");
+      }
+    }
+    assert(MLI.isLoopHeader(Header));
+
+    InSet.clear();
+  }
+}
+
+namespace {
+/// Post-order traversal stack entry.
+struct POStackEntry {
+  MachineBasicBlock *MBB;
+  SmallVector<MachineBasicBlock *, 0> Succs;
+
+  POStackEntry(MachineBasicBlock *MBB, MachineFunction &MF,
+               const MachineLoopInfo &MLI);
+};
+} // end anonymous namespace
+
+static bool LoopContains(const MachineLoop *Loop,
+                         const MachineBasicBlock *MBB) {
+  return Loop ? Loop->contains(MBB) : true;
+}
+
+POStackEntry::POStackEntry(MachineBasicBlock *MBB, MachineFunction &MF,
+                           const MachineLoopInfo &MLI)
+    : MBB(MBB), Succs(MBB->successors()) {
+  // RPO is not a unique form, since at every basic block with multiple
+  // successors, the DFS has to pick which order to visit the successors in.
+  // Sort them strategically (see below).
+  MachineLoop *Loop = MLI.getLoopFor(MBB);
+  MachineFunction::iterator Next = next(MachineFunction::iterator(MBB));
+  MachineBasicBlock *LayoutSucc = Next == MF.end() ? nullptr : &*Next;
+  std::stable_sort(
+      Succs.begin(), Succs.end(),
+      [=, &MLI](const MachineBasicBlock *A, const MachineBasicBlock *B) {
+        if (A == B)
+          return false;
+
+        // Keep loops contiguous by preferring the block that's in the same
+        // loop.
+        bool LoopContainsA = LoopContains(Loop, A);
+        bool LoopContainsB = LoopContains(Loop, B);
+        if (LoopContainsA && !LoopContainsB)
+          return true;
+        if (!LoopContainsA && LoopContainsB)
+          return false;
+
+        // Minimize perturbation by preferring the block which is the immediate
+        // layout successor.
+        if (A == LayoutSucc)
+          return true;
+        if (B == LayoutSucc)
+          return false;
+
+        // TODO: More sophisticated orderings may be profitable here.
+
+        return false;
+      });
+}
+
+/// Return the "bottom" block of a loop. This differs from
+/// MachineLoop::getBottomBlock in that it works even if the loop is
+/// discontiguous.
+static MachineBasicBlock *LoopBottom(const MachineLoop *Loop) {
+  MachineBasicBlock *Bottom = Loop->getHeader();
+  for (MachineBasicBlock *MBB : Loop->blocks())
+    if (MBB->getNumber() > Bottom->getNumber())
+      Bottom = MBB;
+  return Bottom;
+}
+
+/// Sort the blocks in RPO, taking special care to make sure that loops are
+/// contiguous even in the case of split backedges.
+///
+/// TODO: Determine whether RPO is actually worthwhile, or whether we should
+/// move to just a stable-topological-sort-based approach that would preserve
+/// more of the original order.
+static void SortBlocks(MachineFunction &MF, const MachineLoopInfo &MLI) {
+  // Note that we do our own RPO rather than using
+  // "llvm/ADT/PostOrderIterator.h" because we want control over the order that
+  // successors are visited in (see above). Also, we can sort the blocks in the
+  // MachineFunction as we go.
+  SmallPtrSet<MachineBasicBlock *, 16> Visited;
+  SmallVector<POStackEntry, 16> Stack;
+
+  MachineBasicBlock *EntryBlock = &*MF.begin();
+  Visited.insert(EntryBlock);
+  Stack.push_back(POStackEntry(EntryBlock, MF, MLI));
+
+  for (;;) {
+    POStackEntry &Entry = Stack.back();
+    SmallVectorImpl<MachineBasicBlock *> &Succs = Entry.Succs;
+    if (!Succs.empty()) {
+      MachineBasicBlock *Succ = Succs.pop_back_val();
+      if (Visited.insert(Succ).second)
+        Stack.push_back(POStackEntry(Succ, MF, MLI));
+      continue;
+    }
+
+    // Put the block in its position in the MachineFunction.
+    MachineBasicBlock &MBB = *Entry.MBB;
+    MBB.moveBefore(&*MF.begin());
+
+    // Branch instructions may utilize a fallthrough, so update them if a
+    // fallthrough has been added or removed.
+    if (!MBB.empty() && MBB.back().isTerminator() && !MBB.back().isBranch() &&
+        !MBB.back().isBarrier())
+      report_fatal_error(
+          "Non-branch terminator with fallthrough cannot yet be rewritten");
+    if (MBB.empty() || !MBB.back().isTerminator() || MBB.back().isBranch())
+      MBB.updateTerminator();
+
+    Stack.pop_back();
+    if (Stack.empty())
+      break;
+  }
+
+  // Now that we've sorted the blocks in RPO, renumber them.
+  MF.RenumberBlocks();
+
+#ifndef NDEBUG
+  SmallSetVector<MachineLoop *, 8> OnStack;
+
+  // Insert a sentinel representing the degenerate loop that starts at the
+  // function entry block and includes the entire function as a "loop" that
+  // executes once.
+  OnStack.insert(nullptr);
+
+  for (auto &MBB : MF) {
+    assert(MBB.getNumber() >= 0 && "Renumbered blocks should be non-negative.");
+
+    MachineLoop *Loop = MLI.getLoopFor(&MBB);
+    if (Loop && &MBB == Loop->getHeader()) {
+      // Loop header. The loop predecessor should be sorted above, and the other
+      // predecessors should be backedges below.
+      for (auto Pred : MBB.predecessors())
+        assert(
+            (Pred->getNumber() < MBB.getNumber() || Loop->contains(Pred)) &&
+            "Loop header predecessors must be loop predecessors or backedges");
+      assert(OnStack.insert(Loop) && "Loops should be declared at most once.");
+    } else {
+      // Not a loop header. All predecessors should be sorted above.
+      for (auto Pred : MBB.predecessors())
+        assert(Pred->getNumber() < MBB.getNumber() &&
+               "Non-loop-header predecessors should be topologically sorted");
+      assert(OnStack.count(MLI.getLoopFor(&MBB)) &&
+             "Blocks must be nested in their loops");
+    }
+    while (OnStack.size() > 1 && &MBB == LoopBottom(OnStack.back()))
+      OnStack.pop_back();
+  }
+  assert(OnStack.pop_back_val() == nullptr &&
+         "The function entry block shouldn't actually be a loop header");
+  assert(OnStack.empty() &&
+         "Control flow stack pushes and pops should be balanced.");
+#endif
+}
+
+/// Test whether Pred has any terminators explicitly branching to MBB, as
+/// opposed to falling through. Note that it's possible (eg. in unoptimized
+/// code) for a branch instruction to both branch to a block and fallthrough
+/// to it, so we check the actual branch operands to see if there are any
+/// explicit mentions.
+static bool ExplicitlyBranchesTo(MachineBasicBlock *Pred, MachineBasicBlock *MBB) {
+  for (MachineInstr &MI : Pred->terminators())
+    for (MachineOperand &MO : MI.explicit_operands())
+      if (MO.isMBB() && MO.getMBB() == MBB)
+        return true;
+  return false;
+}
+
+/// Insert a BLOCK marker for branches to MBB (if needed).
+static void PlaceBlockMarker(MachineBasicBlock &MBB, MachineFunction &MF,
+                             SmallVectorImpl<MachineBasicBlock *> &ScopeTops,
+                             const WebAssemblyInstrInfo &TII,
+                             const MachineLoopInfo &MLI,
+                             MachineDominatorTree &MDT) {
+  // First compute the nearest common dominator of all forward non-fallthrough
+  // predecessors so that we minimize the time that the BLOCK is on the stack,
+  // which reduces overall stack height.
+  MachineBasicBlock *Header = nullptr;
+  bool IsBranchedTo = false;
+  int MBBNumber = MBB.getNumber();
+  for (MachineBasicBlock *Pred : MBB.predecessors())
+    if (Pred->getNumber() < MBBNumber) {
+      Header = Header ? MDT.findNearestCommonDominator(Header, Pred) : Pred;
+      if (ExplicitlyBranchesTo(Pred, &MBB))
+        IsBranchedTo = true;
+    }
+  if (!Header)
+    return;
+  if (!IsBranchedTo)
+    return;
+
+  assert(&MBB != &MF.front() && "Header blocks shouldn't have predecessors");
+  MachineBasicBlock *LayoutPred = &*prev(MachineFunction::iterator(&MBB));
+
+  // If the nearest common dominator is inside a more deeply nested context,
+  // walk out to the nearest scope which isn't more deeply nested.
+  for (MachineFunction::iterator I(LayoutPred), E(Header); I != E; --I) {
+    if (MachineBasicBlock *ScopeTop = ScopeTops[I->getNumber()]) {
+      if (ScopeTop->getNumber() > Header->getNumber()) {
+        // Skip over an intervening scope.
+        I = next(MachineFunction::iterator(ScopeTop));
+      } else {
+        // We found a scope level at an appropriate depth.
+        Header = ScopeTop;
+        break;
+      }
+    }
+  }
+
+  // If there's a loop which ends just before MBB which contains Header, we can
+  // reuse its label instead of inserting a new BLOCK.
+  for (MachineLoop *Loop = MLI.getLoopFor(LayoutPred);
+       Loop && Loop->contains(LayoutPred); Loop = Loop->getParentLoop())
+    if (Loop && LoopBottom(Loop) == LayoutPred && Loop->contains(Header))
+      return;
+
+  // Decide where in Header to put the BLOCK.
+  MachineBasicBlock::iterator InsertPos;
+  MachineLoop *HeaderLoop = MLI.getLoopFor(Header);
+  if (HeaderLoop && MBB.getNumber() > LoopBottom(HeaderLoop)->getNumber()) {
+    // Header is the header of a loop that does not lexically contain MBB, so
+    // the BLOCK needs to be above the LOOP.
+    InsertPos = Header->begin();
+  } else {
+    // Otherwise, insert the BLOCK as late in Header as we can, but before the
+    // beginning of the local expression tree and any nested BLOCKs.
+    InsertPos = Header->getFirstTerminator();
+    while (InsertPos != Header->begin() &&
+           prev(InsertPos)->definesRegister(WebAssembly::EXPR_STACK) &&
+           prev(InsertPos)->getOpcode() != WebAssembly::LOOP)
+      --InsertPos;
+  }
+
+  // Add the BLOCK.
+  BuildMI(*Header, InsertPos, DebugLoc(), TII.get(WebAssembly::BLOCK))
+      .addMBB(&MBB);
+
+  // Track the farthest-spanning scope that ends at this point.
+  int Number = MBB.getNumber();
+  if (!ScopeTops[Number] ||
+      ScopeTops[Number]->getNumber() > Header->getNumber())
+    ScopeTops[Number] = Header;
+}
+
+/// Insert a LOOP marker for a loop starting at MBB (if it's a loop header).
+static void PlaceLoopMarker(MachineBasicBlock &MBB, MachineFunction &MF,
+                            SmallVectorImpl<MachineBasicBlock *> &ScopeTops,
+                            const WebAssemblyInstrInfo &TII,
+                            const MachineLoopInfo &MLI) {
+  MachineLoop *Loop = MLI.getLoopFor(&MBB);
+  if (!Loop || Loop->getHeader() != &MBB)
+    return;
+
+  // The operand of a LOOP is the first block after the loop. If the loop is the
+  // bottom of the function, insert a dummy block at the end.
+  MachineBasicBlock *Bottom = LoopBottom(Loop);
+  auto Iter = next(MachineFunction::iterator(Bottom));
+  if (Iter == MF.end()) {
+    MachineBasicBlock *Label = MF.CreateMachineBasicBlock();
+    // Give it a fake predecessor so that AsmPrinter prints its label.
+    Label->addSuccessor(Label);
+    MF.push_back(Label);
+    Iter = next(MachineFunction::iterator(Bottom));
+  }
+  MachineBasicBlock *AfterLoop = &*Iter;
+  BuildMI(MBB, MBB.begin(), DebugLoc(), TII.get(WebAssembly::LOOP))
+      .addMBB(AfterLoop);
+
+  // Emit a special no-op telling the asm printer that we need a label to close
+  // the loop scope, even though the destination is only reachable by
+  // fallthrough.
+  if (!Bottom->back().isBarrier())
+    BuildMI(*Bottom, Bottom->end(), DebugLoc(), TII.get(WebAssembly::LOOP_END));
+
+  assert((!ScopeTops[AfterLoop->getNumber()] ||
+          ScopeTops[AfterLoop->getNumber()]->getNumber() < MBB.getNumber()) &&
+         "With RPO we should visit the outer-most loop for a block first.");
+  if (!ScopeTops[AfterLoop->getNumber()])
+    ScopeTops[AfterLoop->getNumber()] = &MBB;
+}
+
+/// Insert LOOP and BLOCK markers at appropriate places.
+static void PlaceMarkers(MachineFunction &MF, const MachineLoopInfo &MLI,
+                         const WebAssemblyInstrInfo &TII,
+                         MachineDominatorTree &MDT) {
+  // For each block whose label represents the end of a scope, record the block
+  // which holds the beginning of the scope. This will allow us to quickly skip
+  // over scoped regions when walking blocks. We allocate one more than the
+  // number of blocks in the function to accommodate for the possible fake block
+  // we may insert at the end.
+  SmallVector<MachineBasicBlock *, 8> ScopeTops(MF.getNumBlockIDs() + 1);
+
+  for (auto &MBB : MF) {
+    // Place the LOOP for MBB if MBB is the header of a loop.
+    PlaceLoopMarker(MBB, MF, ScopeTops, TII, MLI);
+
+    // Place the BLOCK for MBB if MBB is branched to from above.
+    PlaceBlockMarker(MBB, MF, ScopeTops, TII, MLI, MDT);
+  }
+}
+
+#ifndef NDEBUG
+static bool
+IsOnStack(const SmallVectorImpl<std::pair<MachineBasicBlock *, bool>> &Stack,
+          const MachineBasicBlock *MBB) {
+  for (const auto &Pair : Stack)
+    if (Pair.first == MBB)
+      return true;
+  return false;
+}
+#endif
+
+bool WebAssemblyCFGStackify::runOnMachineFunction(MachineFunction &MF) {
+  DEBUG(dbgs() << "********** CFG Stackifying **********\n"
+                  "********** Function: "
+               << MF.getName() << '\n');
+
+  const auto &MLI = getAnalysis<MachineLoopInfo>();
+  auto &MDT = getAnalysis<MachineDominatorTree>();
+  const auto &TII = *MF.getSubtarget<WebAssemblySubtarget>().getInstrInfo();
+
+  // RPO sorting needs all loops to be single-entry.
+  EliminateMultipleEntryLoops(MF, MLI);
+
+  // Sort the blocks in RPO, with contiguous loops.
+  SortBlocks(MF, MLI);
+
+  // Place the BLOCK and LOOP markers to indicate the beginnings of scopes.
+  PlaceMarkers(MF, MLI, TII, MDT);
+
+#ifndef NDEBUG
+  // Verify that block and loop beginnings and endings are in LIFO order, and
+  // that all references to blocks are to blocks on the stack at the point of
+  // the reference.
+  SmallVector<std::pair<MachineBasicBlock *, bool>, 0> Stack;
+  for (auto &MBB : MF) {
+    while (!Stack.empty() && Stack.back().first == &MBB)
+      if (Stack.back().second) {
+        assert(Stack.size() >= 2);
+        Stack.pop_back();
+        Stack.pop_back();
+      } else {
+        assert(Stack.size() >= 1);
+        Stack.pop_back();
+      }
+    for (auto &MI : MBB)
+      switch (MI.getOpcode()) {
+      case WebAssembly::LOOP:
+        Stack.push_back(std::make_pair(&MBB, false));
+        Stack.push_back(std::make_pair(MI.getOperand(0).getMBB(), true));
+        break;
+      case WebAssembly::BLOCK:
+        Stack.push_back(std::make_pair(MI.getOperand(0).getMBB(), false));
+        break;
+      default:
+        // Verify that all referenced blocks are in scope. A reference to a
+        // block with a negative number is invalid, but can happen with inline
+        // asm, so we shouldn't assert on it, but instead let CodeGen properly
+        // fail on it.
+        for (const MachineOperand &MO : MI.explicit_operands())
+          if (MO.isMBB() && MO.getMBB()->getNumber() >= 0)
+            assert(IsOnStack(Stack, MO.getMBB()));
+        break;
+      }
+  }
+  assert(Stack.empty());
+#endif
+
+  return true;
+}