diff --git a/llvm/lib/IR/CMakeLists.txt b/llvm/lib/IR/CMakeLists.txt
index 11259cb..1cc229d 100644
--- a/llvm/lib/IR/CMakeLists.txt
+++ b/llvm/lib/IR/CMakeLists.txt
@@ -43,6 +43,7 @@
   Pass.cpp
   PassManager.cpp
   PassRegistry.cpp
+  SafepointIRVerifier.cpp
   ProfileSummary.cpp
   Statepoint.cpp
   Type.cpp
diff --git a/llvm/lib/IR/Core.cpp b/llvm/lib/IR/Core.cpp
index 4ff0261..192a565 100644
--- a/llvm/lib/IR/Core.cpp
+++ b/llvm/lib/IR/Core.cpp
@@ -50,6 +50,7 @@
   initializePrintModulePassWrapperPass(Registry);
   initializePrintFunctionPassWrapperPass(Registry);
   initializePrintBasicBlockPassPass(Registry);
+  initializeSafepointIRVerifierPass(Registry);
   initializeVerifierLegacyPassPass(Registry);
 }
 
diff --git a/llvm/lib/IR/SafepointIRVerifier.cpp b/llvm/lib/IR/SafepointIRVerifier.cpp
new file mode 100644
index 0000000..52ca16b
--- /dev/null
+++ b/llvm/lib/IR/SafepointIRVerifier.cpp
@@ -0,0 +1,358 @@
+//===-- SafepointIRVerifier.cpp - Verify gc.statepoint invariants ---------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// Run a sanity check on the IR to ensure that Safepoints - if they've been
+// inserted - were inserted correctly.  In particular, look for use of
+// non-relocated values after a safepoint.  It's primary use is to check the
+// correctness of safepoint insertion immediately after insertion, but it can
+// also be used to verify that later transforms have not found a way to break
+// safepoint semenatics.
+//
+// In its current form, this verify checks a property which is sufficient, but
+// not neccessary for correctness.  There are some cases where an unrelocated
+// pointer can be used after the safepoint.  Consider this example:
+//
+//    a = ...
+//    b = ...
+//    (a',b') = safepoint(a,b)
+//    c = cmp eq a b
+//    br c, ..., ....
+//
+// Because it is valid to reorder 'c' above the safepoint, this is legal.  In
+// practice, this is a somewhat uncommon transform, but CodeGenPrep does create
+// idioms like this.  Today, the verifier would report a spurious failure on
+// this case.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/DenseSet.h"
+#include "llvm/ADT/SetOperations.h"
+#include "llvm/ADT/SetVector.h"
+#include "llvm/IR/BasicBlock.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/Intrinsics.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/Value.h"
+#include "llvm/IR/SafepointIRVerifier.h"
+#include "llvm/IR/Statepoint.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/raw_ostream.h"
+
+#define DEBUG_TYPE "safepoint-ir-verifier"
+
+using namespace llvm;
+
+/// This option is used for writing test cases.  Instead of crashing the program
+/// when verification fails, report a message to the console (for FileCheck
+/// usage) and continue execution as if nothing happened.
+static cl::opt<bool> PrintOnly("safepoint-ir-verifier-print-only",
+                               cl::init(false));
+
+static void Verify(const Function &F, const DominatorTree &DT);
+
+struct SafepointIRVerifier : public FunctionPass {
+  static char ID; // Pass identification, replacement for typeid
+  DominatorTree DT;
+  SafepointIRVerifier() : FunctionPass(ID) {
+    initializeSafepointIRVerifierPass(*PassRegistry::getPassRegistry());
+  }
+
+  bool runOnFunction(Function &F) override {
+    DT.recalculate(F);
+    Verify(F, DT);
+    return false; // no modifications
+  }
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.setPreservesAll();
+  }
+
+  StringRef getPassName() const override { return "safepoint verifier"; }
+};
+
+void llvm::verifySafepointIR(Function &F) {
+  SafepointIRVerifier pass;
+  pass.runOnFunction(F);
+}
+
+char SafepointIRVerifier::ID = 0;
+
+FunctionPass *llvm::createSafepointIRVerifierPass() {
+  return new SafepointIRVerifier();
+}
+
+INITIALIZE_PASS_BEGIN(SafepointIRVerifier, "verify-safepoint-ir",
+                      "Safepoint IR Verifier", false, true)
+INITIALIZE_PASS_END(SafepointIRVerifier, "verify-safepoint-ir",
+                    "Safepoint IR Verifier", false, true)
+
+static bool isGCPointerType(Type *T) {
+  if (auto *PT = dyn_cast<PointerType>(T))
+    // For the sake of this example GC, we arbitrarily pick addrspace(1) as our
+    // GC managed heap.  We know that a pointer into this heap needs to be
+    // updated and that no other pointer does.
+    return (1 == PT->getAddressSpace());
+  return false;
+}
+
+static bool containsGCPtrType(Type *Ty) {
+  if (isGCPointerType(Ty))
+    return true;
+  if (VectorType *VT = dyn_cast<VectorType>(Ty))
+    return isGCPointerType(VT->getScalarType());
+  if (ArrayType *AT = dyn_cast<ArrayType>(Ty))
+    return containsGCPtrType(AT->getElementType());
+  if (StructType *ST = dyn_cast<StructType>(Ty))
+    return std::any_of(ST->subtypes().begin(), ST->subtypes().end(),
+                       containsGCPtrType);
+  return false;
+}
+
+// Debugging aid -- prints a [Begin, End) range of values.
+template<typename IteratorTy>
+static void PrintValueSet(raw_ostream &OS, IteratorTy Begin, IteratorTy End) {
+  OS << "[ ";
+  while (Begin != End) {
+    OS << **Begin << " ";
+    ++Begin;
+  }
+  OS << "]";
+}
+
+/// The verifier algorithm is phrased in terms of availability.  The set of
+/// values "available" at a given point in the control flow graph is the set of
+/// correctly relocated value at that point, and is a subset of the set of
+/// definitions dominating that point.
+
+/// State we compute and track per basic block.
+struct BasicBlockState {
+  // Set of values available coming in, before the phi nodes
+  DenseSet<const Value *> AvailableIn;
+
+  // Set of values available going out
+  DenseSet<const Value *> AvailableOut;
+
+  // AvailableOut minus AvailableIn.
+  // All elements are Instructions
+  DenseSet<const Value *> Contribution;
+
+  // True if this block contains a safepoint and thus AvailableIn does not
+  // contribute to AvailableOut.
+  bool Cleared = false;
+};
+
+
+/// Gather all the definitions dominating the start of BB into Result.  This is
+/// simply the Defs introduced by every dominating basic block and the function
+/// arguments.
+static void GatherDominatingDefs(const BasicBlock *BB,
+                                 DenseSet<const Value *> &Result,
+                                 const DominatorTree &DT,
+                    DenseMap<const BasicBlock *, BasicBlockState *> &BlockMap) {
+  DomTreeNode *DTN = DT[const_cast<BasicBlock *>(BB)];
+
+  while (DTN->getIDom()) {
+    DTN = DTN->getIDom();
+    const auto &Defs = BlockMap[DTN->getBlock()]->Contribution;
+    Result.insert(Defs.begin(), Defs.end());
+    // If this block is 'Cleared', then nothing LiveIn to this block can be
+    // available after this block completes.  Note: This turns out to be 
+    // really important for reducing memory consuption of the initial available
+    // sets and thus peak memory usage by this verifier.
+    if (BlockMap[DTN->getBlock()]->Cleared)
+      return;
+  }
+
+  for (const Argument &A : BB->getParent()->args())
+    if (containsGCPtrType(A.getType()))
+      Result.insert(&A);
+}
+
+/// Model the effect of an instruction on the set of available values.
+static void TransferInstruction(const Instruction &I, bool &Cleared,
+                              DenseSet<const Value *> &Available) {
+  if (isStatepoint(I)) {
+    Cleared = true;
+    Available.clear();
+  } else if (containsGCPtrType(I.getType()))
+    Available.insert(&I);
+}
+
+/// Compute the AvailableOut set for BB, based on the
+/// BasicBlockState BBS, which is the BasicBlockState for BB. FirstPass is set
+/// when the verifier runs for the first time computing the AvailableOut set
+/// for BB.
+static void TransferBlock(const BasicBlock *BB,
+                          BasicBlockState &BBS, bool FirstPass) {
+
+  const DenseSet<const Value *> &AvailableIn = BBS.AvailableIn; 
+  DenseSet<const Value *> &AvailableOut  = BBS.AvailableOut;
+
+  if (BBS.Cleared) {
+    // AvailableOut does not change no matter how the input changes, just
+    // leave it be.  We need to force this calculation the first time so that
+    // we have a AvailableOut at all.
+    if (FirstPass) {
+      AvailableOut = BBS.Contribution;
+    }
+  } else {
+    // Otherwise, we need to reduce the AvailableOut set by things which are no
+    // longer in our AvailableIn
+    DenseSet<const Value *> Temp = BBS.Contribution;
+    set_union(Temp, AvailableIn);
+    AvailableOut = std::move(Temp);
+  }
+
+  DEBUG(dbgs() << "Transfered block " << BB->getName() << " from ";
+        PrintValueSet(dbgs(), AvailableIn.begin(), AvailableIn.end());
+        dbgs() << " to ";
+        PrintValueSet(dbgs(), AvailableOut.begin(), AvailableOut.end());
+        dbgs() << "\n";);
+}
+
+/// Return true if V is exclusively derived off a constant base, i.e. all
+/// operands of non-unary operators (phi/select) are derived off a constant
+/// base.
+static bool
+isExclusivelyConstantDerivedRecursive(const Value *V,
+                                      DenseSet<const Value *> &Visited) {
+  if (!Visited.insert(V).second)
+    return true;
+
+  if (isa<Constant>(V))
+    return true;
+
+  if (const auto *CI = dyn_cast<CastInst>(V))
+    return isExclusivelyConstantDerivedRecursive(CI->stripPointerCasts(),
+                                                 Visited);
+
+  if (const auto *GEP = dyn_cast<GetElementPtrInst>(V))
+    return isExclusivelyConstantDerivedRecursive(GEP->getPointerOperand(),
+                                                 Visited);
+
+  // All operands of the phi and select nodes should be derived off a constant
+  // base.
+  if (const auto *PN = dyn_cast<PHINode>(V)) {
+    return all_of(PN->incoming_values(), [&](const Value *InV) {
+      return isExclusivelyConstantDerivedRecursive(InV, Visited);
+    });
+  }
+
+  if (const auto *SI = dyn_cast<SelectInst>(V))
+    return isExclusivelyConstantDerivedRecursive(SI->getTrueValue(), Visited) &&
+           isExclusivelyConstantDerivedRecursive(SI->getFalseValue(), Visited);
+
+  return false;
+}
+
+static bool isExclusivelyConstantDerived(const Value *V) {
+  DenseSet<const Value*> Visited;
+  return isExclusivelyConstantDerivedRecursive(V, Visited);
+}
+
+static void Verify(const Function &F, const DominatorTree &DT) {
+  SpecificBumpPtrAllocator<BasicBlockState> BSAllocator;
+  DenseMap<const BasicBlock *, BasicBlockState *> BlockMap;
+ 
+  DEBUG(dbgs() << "Verifying gc pointers in function: " << F.getName() << "\n");
+  if (PrintOnly)
+    dbgs() << "Verifying gc pointers in function: " << F.getName() << "\n";
+
+
+  for (const BasicBlock &BB : F) {
+    BasicBlockState *BBS = new(BSAllocator.Allocate()) BasicBlockState;
+    for (const auto &I : BB)
+      TransferInstruction(I, BBS->Cleared, BBS->Contribution);
+    BlockMap[&BB] = BBS;
+  }
+
+  for (auto &BBI : BlockMap) {
+    GatherDominatingDefs(BBI.first, BBI.second->AvailableIn, DT, BlockMap);
+    TransferBlock(BBI.first, *BBI.second, true);
+  }
+
+  SetVector<const BasicBlock *> Worklist;
+  for (auto &BBI : BlockMap)
+    Worklist.insert(BBI.first);
+
+  // This loop iterates the AvailableIn and AvailableOut sets to a fixed point.
+  // The AvailableIn and AvailableOut sets decrease as we iterate.
+  while (!Worklist.empty()) {
+    const BasicBlock *BB = Worklist.pop_back_val();
+    BasicBlockState *BBS = BlockMap[BB];
+
+    size_t OldInCount = BBS->AvailableIn.size();
+    for (const BasicBlock *PBB : predecessors(BB))
+      set_intersect(BBS->AvailableIn, BlockMap[PBB]->AvailableOut);
+
+    if (OldInCount == BBS->AvailableIn.size())
+      continue;
+
+    assert(OldInCount > BBS->AvailableIn.size() && "invariant!");
+
+    size_t OldOutCount = BBS->AvailableOut.size();
+    TransferBlock(BB, *BBS, false);
+    if (OldOutCount != BBS->AvailableOut.size()) {
+      assert(OldOutCount > BBS->AvailableOut.size() && "invariant!");
+      Worklist.insert(succ_begin(BB), succ_end(BB));
+    }
+  }
+
+  // We now have all the information we need to decide if the use of a heap
+  // reference is legal or not, given our safepoint semantics.
+
+  bool AnyInvalidUses = false;
+
+  auto ReportInvalidUse = [&AnyInvalidUses](const Value &V,
+                                            const Instruction &I) {
+    errs() << "Illegal use of unrelocated value found!\n";
+    errs() << "Def: " << V << "\n";
+    errs() << "Use: " << I << "\n";
+    if (!PrintOnly)
+      abort();
+    AnyInvalidUses = true;
+  };
+
+  for (const BasicBlock &BB : F) {
+    // We destructively modify AvailableIn as we traverse the block instruction
+    // by instruction.
+    DenseSet<const Value *> &AvailableSet = BlockMap[&BB]->AvailableIn;
+    for (const Instruction &I : BB) {
+      if (const PHINode *PN = dyn_cast<PHINode>(&I)) {
+        if (containsGCPtrType(PN->getType()))
+          for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
+            const BasicBlock *InBB = PN->getIncomingBlock(i);
+            const Value *InValue = PN->getIncomingValue(i);
+
+            if (!isExclusivelyConstantDerived(InValue) &&
+                !BlockMap[InBB]->AvailableOut.count(InValue))
+              ReportInvalidUse(*InValue, *PN);
+          }
+      } else {
+        for (const Value *V : I.operands())
+          if (containsGCPtrType(V->getType()) &&
+              !isExclusivelyConstantDerived(V) && !AvailableSet.count(V))
+            ReportInvalidUse(*V, I);
+      }
+
+      bool Cleared = false;
+      TransferInstruction(I, Cleared, AvailableSet);
+      (void)Cleared;
+    }
+  }
+
+  if (PrintOnly && !AnyInvalidUses) {
+    dbgs() << "No illegal uses found by SafepointIRVerifier in: " << F.getName()
+           << "\n";
+  }
+}