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diff --git a/lib/Target/WebAssembly/WebAssemblyOptimizeLiveIntervals.cpp b/lib/Target/WebAssembly/WebAssemblyOptimizeLiveIntervals.cpp
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index 000000000000..473de7ddae7e
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+++ b/lib/Target/WebAssembly/WebAssemblyOptimizeLiveIntervals.cpp
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+//===--- WebAssemblyOptimizeLiveIntervals.cpp - LiveInterval processing ---===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// \brief Optimize LiveIntervals for use in a post-RA context.
+//
+/// LiveIntervals normally runs before register allocation when the code is
+/// only recently lowered out of SSA form, so it's uncommon for registers to
+/// have multiple defs, and then they do, the defs are usually closely related.
+/// Later, after coalescing, tail duplication, and other optimizations, it's
+/// more common to see registers with multiple unrelated defs. This pass
+/// updates LiveIntervalAnalysis to distribute the value numbers across separate
+/// LiveIntervals.
+///
+//===----------------------------------------------------------------------===//
+
+#include "WebAssembly.h"
+#include "WebAssemblySubtarget.h"
+#include "llvm/CodeGen/LiveIntervalAnalysis.h"
+#include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
+#include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+using namespace llvm;
+
+#define DEBUG_TYPE "wasm-optimize-live-intervals"
+
+namespace {
+class WebAssemblyOptimizeLiveIntervals final : public MachineFunctionPass {
+  const char *getPassName() const override {
+    return "WebAssembly Optimize Live Intervals";
+  }
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.setPreservesCFG();
+    AU.addRequired<LiveIntervals>();
+    AU.addPreserved<MachineBlockFrequencyInfo>();
+    AU.addPreserved<SlotIndexes>();
+    AU.addPreserved<LiveIntervals>();
+    AU.addPreservedID(LiveVariablesID);
+    AU.addPreservedID(MachineDominatorsID);
+    MachineFunctionPass::getAnalysisUsage(AU);
+  }
+
+  bool runOnMachineFunction(MachineFunction &MF) override;
+
+public:
+  static char ID; // Pass identification, replacement for typeid
+  WebAssemblyOptimizeLiveIntervals() : MachineFunctionPass(ID) {}
+};
+} // end anonymous namespace
+
+char WebAssemblyOptimizeLiveIntervals::ID = 0;
+FunctionPass *llvm::createWebAssemblyOptimizeLiveIntervals() {
+  return new WebAssemblyOptimizeLiveIntervals();
+}
+
+bool WebAssemblyOptimizeLiveIntervals::runOnMachineFunction(MachineFunction &MF) {
+  DEBUG(dbgs() << "********** Optimize LiveIntervals **********\n"
+                  "********** Function: "
+               << MF.getName() << '\n');
+
+  MachineRegisterInfo &MRI = MF.getRegInfo();
+  LiveIntervals &LIS = getAnalysis<LiveIntervals>();
+
+  // We don't preserve SSA form.
+  MRI.leaveSSA();
+
+  assert(MRI.tracksLiveness() &&
+         "OptimizeLiveIntervals expects liveness");
+
+  // Split multiple-VN LiveIntervals into multiple LiveIntervals.
+  SmallVector<LiveInterval*, 4> SplitLIs;
+  for (unsigned i = 0, e = MRI.getNumVirtRegs(); i < e; ++i) {
+    unsigned Reg = TargetRegisterInfo::index2VirtReg(i);
+    if (MRI.reg_nodbg_empty(Reg))
+      continue;
+
+    LIS.splitSeparateComponents(LIS.getInterval(Reg), SplitLIs);
+    SplitLIs.clear();
+  }
+
+  // In PrepareForLiveIntervals, we conservatively inserted IMPLICIT_DEF
+  // instructions to satisfy LiveIntervals' requirement that all uses be
+  // dominated by defs. Now that LiveIntervals has computed which of these
+  // defs are actually needed and which are dead, remove the dead ones.
+  for (auto MII = MF.begin()->begin(), MIE = MF.begin()->end(); MII != MIE; ) {
+    MachineInstr *MI = &*MII++;
+    if (MI->isImplicitDef() && MI->getOperand(0).isDead()) {
+      LiveInterval &LI = LIS.getInterval(MI->getOperand(0).getReg());
+      LIS.removeVRegDefAt(LI, LIS.getInstructionIndex(*MI).getRegSlot());
+      LIS.RemoveMachineInstrFromMaps(*MI);
+      MI->eraseFromParent();
+    }
+  }
+
+  return false;
+}