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diff --git a/contrib/llvm/lib/Transforms/Scalar/LowerGuardIntrinsic.cpp b/contrib/llvm/lib/Transforms/Scalar/LowerGuardIntrinsic.cpp
new file mode 100644
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+++ b/contrib/llvm/lib/Transforms/Scalar/LowerGuardIntrinsic.cpp
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+//===- LowerGuardIntrinsic.cpp - Lower the guard intrinsic ---------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass lowers the llvm.experimental.guard intrinsic to a conditional call
+// to @llvm.experimental.deoptimize.  Once this happens, the guard can no longer
+// be widened.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/IR/BasicBlock.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/InstIterator.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/Intrinsics.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/MDBuilder.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Pass.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
+
+using namespace llvm;
+
+static cl::opt<uint32_t> PredicatePassBranchWeight(
+    "guards-predicate-pass-branch-weight", cl::Hidden, cl::init(1 << 20),
+    cl::desc("The probability of a guard failing is assumed to be the "
+             "reciprocal of this value (default = 1 << 20)"));
+
+namespace {
+struct LowerGuardIntrinsic : public FunctionPass {
+  static char ID;
+  LowerGuardIntrinsic() : FunctionPass(ID) {
+    initializeLowerGuardIntrinsicPass(*PassRegistry::getPassRegistry());
+  }
+
+  bool runOnFunction(Function &F) override;
+};
+}
+
+static void MakeGuardControlFlowExplicit(Function *DeoptIntrinsic,
+                                         CallInst *CI) {
+  OperandBundleDef DeoptOB(*CI->getOperandBundle(LLVMContext::OB_deopt));
+  SmallVector<Value *, 4> Args(std::next(CI->arg_begin()), CI->arg_end());
+
+  auto *CheckBB = CI->getParent();
+  auto *DeoptBlockTerm =
+      SplitBlockAndInsertIfThen(CI->getArgOperand(0), CI, true);
+
+  auto *CheckBI = cast<BranchInst>(CheckBB->getTerminator());
+
+  // SplitBlockAndInsertIfThen inserts control flow that branches to
+  // DeoptBlockTerm if the condition is true.  We want the opposite.
+  CheckBI->swapSuccessors();
+
+  CheckBI->getSuccessor(0)->setName("guarded");
+  CheckBI->getSuccessor(1)->setName("deopt");
+
+  if (auto *MD = CI->getMetadata(LLVMContext::MD_make_implicit))
+    CheckBI->setMetadata(LLVMContext::MD_make_implicit, MD);
+
+  MDBuilder MDB(CI->getContext());
+  CheckBI->setMetadata(LLVMContext::MD_prof,
+                       MDB.createBranchWeights(PredicatePassBranchWeight, 1));
+
+  IRBuilder<> B(DeoptBlockTerm);
+  auto *DeoptCall = B.CreateCall(DeoptIntrinsic, Args, {DeoptOB}, "");
+
+  if (DeoptIntrinsic->getReturnType()->isVoidTy()) {
+    B.CreateRetVoid();
+  } else {
+    DeoptCall->setName("deoptcall");
+    B.CreateRet(DeoptCall);
+  }
+
+  DeoptCall->setCallingConv(CI->getCallingConv());
+  DeoptBlockTerm->eraseFromParent();
+}
+
+bool LowerGuardIntrinsic::runOnFunction(Function &F) {
+  // Check if we can cheaply rule out the possibility of not having any work to
+  // do.
+  auto *GuardDecl = F.getParent()->getFunction(
+      Intrinsic::getName(Intrinsic::experimental_guard));
+  if (!GuardDecl || GuardDecl->use_empty())
+    return false;
+
+  SmallVector<CallInst *, 8> ToLower;
+  for (auto &I : instructions(F))
+    if (auto *CI = dyn_cast<CallInst>(&I))
+      if (auto *F = CI->getCalledFunction())
+        if (F->getIntrinsicID() == Intrinsic::experimental_guard)
+          ToLower.push_back(CI);
+
+  if (ToLower.empty())
+    return false;
+
+  auto *DeoptIntrinsic = Intrinsic::getDeclaration(
+      F.getParent(), Intrinsic::experimental_deoptimize, {F.getReturnType()});
+  DeoptIntrinsic->setCallingConv(GuardDecl->getCallingConv());
+
+  for (auto *CI : ToLower) {
+    MakeGuardControlFlowExplicit(DeoptIntrinsic, CI);
+    CI->eraseFromParent();
+  }
+
+  return true;
+}
+
+char LowerGuardIntrinsic::ID = 0;
+INITIALIZE_PASS(LowerGuardIntrinsic, "lower-guard-intrinsic",
+                "Lower the guard intrinsic to normal control flow", false,
+                false)
+
+Pass *llvm::createLowerGuardIntrinsicPass() {
+  return new LowerGuardIntrinsic();
+}