Add MemoryAccess creation and PHI creation APIs to MemorySSA

[• dberlin]

(it looks like clang-format fixed some whitespace in the unittest, i'll fix formatting separately and rebase prior to commit)

[george.burgess.iv]

Looks good overall -- just a few nits.

include/llvm/Transforms/Utils/MemorySSA.h

553

createMemoryAccessInBB, maybe? Naming is hard.

557

///

lib/Transforms/Utils/MemorySSA.cpp

588

Please remove this newline

594

Bring this out of the loop + clear on each iteration, please.

601

Varying compare-against-null styles?

[• dberlin]

• Update for review comments

[• dberlin]

Update to fix nits

[george.burgess.iv]

LGTM. Thanks for the patch!

include/llvm/Transforms/Utils/MemorySSA.h

public:
 
   /// \brief Return the number of incoming edges
   unsigned getNumIncomingValues() const { return getNumOperands(); }
 
   /// \brief Return incoming value number x
   MemoryAccess *getIncomingValue(unsigned I) const { return getOperand(I); }
   void setIncomingValue(unsigned I, MemoryAccess *V) {
     assert(V && "PHI node got a null value!");
-    assert(getType() == V->getType() &&
-           "All operands to PHI node must be the same type as the PHI node!");
     setOperand(I, V);
   }
   static unsigned getOperandNumForIncomingValue(unsigned I) { return I; }
   static unsigned getIncomingValueNumForOperand(unsigned I) { return I; }
 
   /// \brief Return incoming basic block number @p i.
   BasicBlock *getIncomingBlock(unsigned I) const { return block_begin()[I]; }
 
public:
   /// \brief Return the list of MemoryAccess's for a given basic block.
   ///
   /// This list is not modifiable by the user.
   const AccessList *getBlockAccesses(const BasicBlock *BB) const {
     auto It = PerBlockAccesses.find(BB);
     return It == PerBlockAccesses.end() ? nullptr : It->second.get();
   }
 
+  /// \brief Create an empty MemoryPhi in MemorySSA
+  MemoryPhi *createMemoryPhi(BasicBlock *BB);
+
+  enum InsertionPlace { Beginning, End };
+
+  /// \brief Create a MemoryAccess in MemorySSA at a specified point in a block,
+  /// with a specified clobbering definition.
+  ///
+  /// Returns the new MemoryAccess.
+  /// This should be called when a memory instruction is created that is being
+  /// used to replace an existing memory instruction. It will *not* create PHI
+  /// nodes, or verify the clobbering definition. The insertion place is used
+  /// solely to determine where in the memoryssa access lists the instruction
+  /// will be placed. The caller is expected to keep ordering the same as
+  /// instructions.
+  /// It will return the new MemoryAccess.
+  MemoryAccess *createMemoryAccessInBB(Instruction *I, MemoryAccess *Definition,
+                                       const BasicBlock *BB,
+                                       InsertionPlace Point);
+  /// \brief Create a MemoryAccess in MemorySSA before or after an existing
+  /// MemoryAccess.
+  ///
+  /// Returns the new MemoryAccess.
+  /// This should be called when a memory instruction is created that is being
+  /// used to replace an existing memory instruction. It will *not* create PHI
+  /// nodes, or verify the clobbering definition.  The clobbering definition
+  /// must be non-null.
+  MemoryAccess *createMemoryAccessBefore(Instruction *I,
+                                         MemoryAccess *Definition,
+                                         MemoryAccess *InsertPt);
+  MemoryAccess *createMemoryAccessAfter(Instruction *I,
+                                        MemoryAccess *Definition,
+                                        MemoryAccess *InsertPt);
+
   /// \brief Remove a MemoryAccess from MemorySSA, including updating all
   /// definitions and uses.
   /// This should be called when a memory instruction that has a MemoryAccess
   /// associated with it is erased from the program.  For example, if a store or
   /// load is simply erased (not replaced), removeMemoryAccess should be called
   /// on the MemoryAccess for that store/load.
   void removeMemoryAccess(MemoryAccess *);
 
-  enum InsertionPlace { Beginning, End };
-
   /// \brief Given two memory accesses in the same basic block, determine
   /// whether MemoryAccess \p A dominates MemoryAccess \p B.
   bool locallyDominates(const MemoryAccess *A, const MemoryAccess *B) const;
 
   /// \brief Verify that MemorySSA is self consistent (IE definitions dominate
   /// all uses, uses appear in the right places).  This is used by unit tests.
   void verifyMemorySSA() const;
 
 protected:
   // Used by Memory SSA annotater, dumpers, and wrapper pass
   friend class MemorySSAAnnotatedWriter;
   friend class MemorySSAPrinterLegacyPass;
   void verifyDefUses(Function &F) const;
   void verifyDomination(Function &F) const;
+  void verifyOrdering(Function &F) const;
 
 private:
   void verifyUseInDefs(MemoryAccess *, MemoryAccess *) const;
   using AccessMap = DenseMap<const BasicBlock *, std::unique_ptr<AccessList>>;
 
   void
   determineInsertionPoint(const SmallPtrSetImpl<BasicBlock *> &DefiningBlocks);
   void computeDomLevels(DenseMap<DomTreeNode *, unsigned> &DomLevels);
   void markUnreachableAsLiveOnEntry(BasicBlock *BB);
   bool dominatesUse(const MemoryAccess *, const MemoryAccess *) const;
   MemoryUseOrDef *createNewAccess(Instruction *);
+  MemoryUseOrDef *createDefinedAccess(Instruction *, MemoryAccess *);
   MemoryAccess *findDominatingDef(BasicBlock *, enum InsertionPlace);
   void removeFromLookups(MemoryAccess *);
 
   MemoryAccess *renameBlock(BasicBlock *, MemoryAccess *);
   void renamePass(DomTreeNode *, MemoryAccess *IncomingVal,
                   SmallPtrSet<BasicBlock *, 16> &Visited);
-  AccessList *getOrCreateAccessList(BasicBlock *);
+  AccessList *getOrCreateAccessList(const BasicBlock *);
   AliasAnalysis *AA;
   DominatorTree *DT;
   Function &F;
 
   // Memory SSA mappings
   DenseMap<const Value *, MemoryAccess *> ValueToMemoryAccess;
   AccessMap PerBlockAccesses;
   std::unique_ptr<MemoryAccess> LiveOnEntryDef;

lib/Transforms/Utils/MemorySSA.cpp

 
 MemorySSA::~MemorySSA() {
   // Drop all our references
   for (const auto &Pair : PerBlockAccesses)
     for (MemoryAccess &MA : *Pair.second)
       MA.dropAllReferences();
 }
 
-MemorySSA::AccessList *MemorySSA::getOrCreateAccessList(BasicBlock *BB) {
+MemorySSA::AccessList *MemorySSA::getOrCreateAccessList(const BasicBlock *BB) {
   auto Res = PerBlockAccesses.insert(std::make_pair(BB, nullptr));
 
   if (Res.second)
     Res.first->second = make_unique<AccessList>();
   return Res.first->second.get();
 }
 
 MemorySSAWalker *MemorySSA::getWalker() {
MemorySSAWalker *MemorySSA::getWalker() {
   IDFs.setLiveInBlocks(LiveInBlocks);
   SmallVector<BasicBlock *, 32> IDFBlocks;
   IDFs.calculate(IDFBlocks);
 
   // Now place MemoryPhi nodes.
   for (auto &BB : IDFBlocks) {
     // Insert phi node
     AccessList *Accesses = getOrCreateAccessList(BB);
-    MemoryPhi *Phi = new MemoryPhi(F.getContext(), BB, NextID++);
+    MemoryPhi *Phi = new MemoryPhi(BB->getContext(), BB, NextID++);
     ValueToMemoryAccess.insert(std::make_pair(BB, Phi));
     // Phi's always are placed at the front of the block.
     Accesses->push_front(Phi);
   }
 
   // Now do regular SSA renaming on the MemoryDef/MemoryUse. Visited will get
   // filled in with all blocks.
   SmallPtrSet<BasicBlock *, 16> Visited;
MemorySSAWalker *MemorySSA::getWalker() {
   // somewhere.
   for (auto &BB : F)
     if (!Visited.count(&BB))
       markUnreachableAsLiveOnEntry(&BB);
 
   return Walker.get();
 }
 
+MemoryPhi *MemorySSA::createMemoryPhi(BasicBlock *BB) {
+  assert(!getMemoryAccess(BB) && "MemoryPhi already exists for this BB");
+  AccessList *Accesses = getOrCreateAccessList(BB);
+  MemoryPhi *Phi = new MemoryPhi(BB->getContext(), BB, NextID++);
+  ValueToMemoryAccess.insert(std::make_pair(BB, Phi));
+  // Phi's always are placed at the front of the block.
+  Accesses->push_front(Phi);
+  return Phi;
+}
+
+MemoryUseOrDef *MemorySSA::createDefinedAccess(Instruction *I,
+                                               MemoryAccess *Definition) {
+  assert(!isa<PHINode>(I) && "Cannot create a defined access for a PHI");
+  MemoryUseOrDef *NewAccess = createNewAccess(I);
+  assert(
+      NewAccess != nullptr &&
+      "Tried to create a memory access for a non-memory touching instruction");
+  NewAccess->setDefiningAccess(Definition);
+  return NewAccess;
+}
+
+MemoryAccess *MemorySSA::createMemoryAccessInBB(Instruction *I,
+                                                MemoryAccess *Definition,
+                                                const BasicBlock *BB,
+                                                InsertionPlace Point) {
+  MemoryUseOrDef *NewAccess = createDefinedAccess(I, Definition);
+  auto *Accesses = getOrCreateAccessList(BB);
+  if (Point == Beginning) {
+    // It goes after any phi nodes
+    auto AI = std::find_if(
+        Accesses->begin(), Accesses->end(),
+        [](const MemoryAccess &MA) { return !isa<MemoryPhi>(MA); });
+
+    Accesses->insert(AI, NewAccess);
+  } else {
+    Accesses->push_back(NewAccess);
+  }
+
+  return NewAccess;
+}
+MemoryAccess *MemorySSA::createMemoryAccessBefore(Instruction *I,
+                                                  MemoryAccess *Definition,
+                                                  MemoryAccess *InsertPt) {
+  assert(I->getParent() == InsertPt->getBlock() &&
+         "New and old access must be in the same block");
+  MemoryUseOrDef *NewAccess = createDefinedAccess(I, Definition);
+  auto *Accesses = getOrCreateAccessList(InsertPt->getBlock());
+  Accesses->insert(AccessList::iterator(InsertPt), NewAccess);
+  return NewAccess;
+}
+
+MemoryAccess *MemorySSA::createMemoryAccessAfter(Instruction *I,
+                                                 MemoryAccess *Definition,
+                                                 MemoryAccess *InsertPt) {
+  assert(I->getParent() == InsertPt->getBlock() &&
+         "New and old access must be in the same block");
+  MemoryUseOrDef *NewAccess = createDefinedAccess(I, Definition);
+  auto *Accesses = getOrCreateAccessList(InsertPt->getBlock());
+  Accesses->insertAfter(AccessList::iterator(InsertPt), NewAccess);
+  return NewAccess;
+}
+
 /// \brief Helper function to create new memory accesses
 MemoryUseOrDef *MemorySSA::createNewAccess(Instruction *I) {
   // The assume intrinsic has a control dependency which we model by claiming
   // that it writes arbitrarily. Ignore that fake memory dependency here.
   // FIXME: Replace this special casing with a more accurate modelling of
   // assume's control dependency.
   if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I))
     if (II->getIntrinsicID() == Intrinsic::assume)

 void MemorySSA::dump() const {
   MemorySSAAnnotatedWriter Writer(this);
   F.print(dbgs(), &Writer);
 }
 
 void MemorySSA::verifyMemorySSA() const {
   verifyDefUses(F);
   verifyDomination(F);
+  verifyOrdering(F);
+}
+
+/// \brief Verify that the order and existence of MemoryAccesses matches the
+/// order and existence of memory affecting instructions.
+void MemorySSA::verifyOrdering(Function &F) const {
+  // Walk all the blocks, comparing what the lookups think and what the access
+  // lists think, as well as the order in the blocks vs the order in the access
+  // lists.
+  SmallVector<MemoryAccess *, 32> ActualAccesses;
+  for (BasicBlock &B : F) {
+    const AccessList *AL = getBlockAccesses(&B);
+    MemoryAccess *Phi = getMemoryAccess(&B);
+    if (Phi)
+      ActualAccesses.push_back(Phi);
+    for (Instruction &I : B) {
+      MemoryAccess *MA = getMemoryAccess(&I);
+      assert((!MA || AL) && "We have memory affecting instructions "
+                            "in this block but they are not in the "
+                            "access list");
+      if (MA)
+        ActualAccesses.push_back(MA);
+    }
+    // Either we hit the assert, really have no accesses, or we have both
+    // accesses and an access list
+    if (!AL)
+      continue;
+    assert(AL->size() == ActualAccesses.size() &&
+           "We don't have the same number of accesses in the block as on the "
+           "access list");
+    auto ALI = AL->begin();
+    auto AAI = ActualAccesses.begin();
+    while (ALI != AL->end() && AAI != ActualAccesses.end()) {
+      assert(&*ALI == *AAI && "Not the same accesses in the same order");
+      ++ALI;
+      ++AAI;
+    }
+    ActualAccesses.clear();
+  }
 }
 
 /// \brief Verify the domination properties of MemorySSA by checking that each
 /// definition dominates all of its uses.
 void MemorySSA::verifyDomination(Function &F) const {
   for (BasicBlock &B : F) {
     // Phi nodes are attached to basic blocks
     if (MemoryPhi *MP = getMemoryAccess(&B)) {

 }
 
 /// \brief Verify the immediate use information, by walking all the memory
 /// accesses and verifying that, for each use, it appears in the
 /// appropriate def's use list
 void MemorySSA::verifyDefUses(Function &F) const {
   for (BasicBlock &B : F) {
     // Phi nodes are attached to basic blocks
-    if (MemoryPhi *Phi = getMemoryAccess(&B))
+    if (MemoryPhi *Phi = getMemoryAccess(&B)) {
+      assert(Phi->getNumOperands() ==
+                 std::distance(pred_begin(&B), pred_end(&B)) &&
+             "Incomplete MemoryPhi Node");
       for (unsigned I = 0, E = Phi->getNumIncomingValues(); I != E; ++I)
         verifyUseInDefs(Phi->getIncomingValue(I), Phi);
+    }
 
     for (Instruction &I : B) {
       if (MemoryAccess *MA = getMemoryAccess(&I)) {
         assert(isa<MemoryUseOrDef>(MA) &&
                "Found a phi node not attached to a bb");
         verifyUseInDefs(cast<MemoryUseOrDef>(MA)->getDefiningAccess(), MA);
       }
     }

unittests/Transforms/Utils/MemorySSA.cpp

 //===- MemorySSA.cpp - Unit tests for MemorySSA ---------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
-#include "llvm/IR/DataLayout.h"
 #include "llvm/Transforms/Utils/MemorySSA.h"
 #include "llvm/Analysis/AliasAnalysis.h"
 #include "llvm/Analysis/BasicAliasAnalysis.h"
 #include "llvm/IR/BasicBlock.h"
+#include "llvm/IR/DataLayout.h"
 #include "llvm/IR/Dominators.h"
 #include "llvm/IR/IRBuilder.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/LLVMContext.h"
 #include "gtest/gtest.h"
 
 using namespace llvm;
 
void setupAnalyses() {
     Analyses.reset(new TestAnalyses(*this));
   }
 
 public:
   MemorySSATest()
       : M("MemorySSATest", C), B(C), DL(DLString), TLI(TLII), F(nullptr) {}
 };
 
+TEST_F(MemorySSATest, CreateALoadAndPhi) {
+  // We create a diamond where there is a store on one side, and then after
+  // running memory ssa, create a load after the merge point, and use it to test
+  // updating by creating an access for the load and a memoryphi.
+  F = Function::Create(
+      FunctionType::get(B.getVoidTy(), {B.getInt8PtrTy()}, false),
+      GlobalValue::ExternalLinkage, "F", &M);
+  BasicBlock *Entry(BasicBlock::Create(C, "", F));
+  BasicBlock *Left(BasicBlock::Create(C, "", F));
+  BasicBlock *Right(BasicBlock::Create(C, "", F));
+  BasicBlock *Merge(BasicBlock::Create(C, "", F));
+  B.SetInsertPoint(Entry);
+  B.CreateCondBr(B.getTrue(), Left, Right);
+  B.SetInsertPoint(Left);
+  Argument *PointerArg = &*F->arg_begin();
+  StoreInst *StoreInst = B.CreateStore(B.getInt8(16), PointerArg);
+  BranchInst::Create(Merge, Left);
+  BranchInst::Create(Merge, Right);
+
+  setupAnalyses();
+  MemorySSA &MSSA = Analyses->MSSA;
+  // Add the load
+  B.SetInsertPoint(Merge);
+  LoadInst *LoadInst = B.CreateLoad(PointerArg);
+  // Should be no phi to start
+  EXPECT_EQ(MSSA.getMemoryAccess(Merge), nullptr);
+
+  // Create the phi
+  MemoryPhi *MP = MSSA.createMemoryPhi(Merge);
+  MemoryDef *StoreAccess = cast<MemoryDef>(MSSA.getMemoryAccess(StoreInst));
+  MP->addIncoming(StoreAccess, Left);
+  MP->addIncoming(MSSA.getLiveOnEntryDef(), Right);
+
+  // Create the load memory acccess
+  MemoryUse *LoadAccess = cast<MemoryUse>(
+      MSSA.createMemoryAccessInBB(LoadInst, MP, Merge, MemorySSA::Beginning));
+  MemoryAccess *DefiningAccess = LoadAccess->getDefiningAccess();
+  EXPECT_TRUE(isa<MemoryPhi>(DefiningAccess));
+  MSSA.verifyMemorySSA();
+}
+
+TEST_F(MemorySSATest, RemoveAPhi) {
+  // We create a diamond where there is a store on one side, and then a load
+  // after the merge point.  This enables us to test a bunch of different
+  // removal cases.
+  F = Function::Create(
+      FunctionType::get(B.getVoidTy(), {B.getInt8PtrTy()}, false),
+      GlobalValue::ExternalLinkage, "F", &M);
+  BasicBlock *Entry(BasicBlock::Create(C, "", F));
+  BasicBlock *Left(BasicBlock::Create(C, "", F));
+  BasicBlock *Right(BasicBlock::Create(C, "", F));
+  BasicBlock *Merge(BasicBlock::Create(C, "", F));
+  B.SetInsertPoint(Entry);
+  B.CreateCondBr(B.getTrue(), Left, Right);
+  B.SetInsertPoint(Left);
+  Argument *PointerArg = &*F->arg_begin();
+  StoreInst *StoreInst = B.CreateStore(B.getInt8(16), PointerArg);
+  BranchInst::Create(Merge, Left);
+  BranchInst::Create(Merge, Right);
+  B.SetInsertPoint(Merge);
+  LoadInst *LoadInst = B.CreateLoad(PointerArg);
+
+  setupAnalyses();
+  MemorySSA &MSSA = Analyses->MSSA;
+  // Before, the load will be a use of a phi<store, liveonentry>.
+  MemoryUse *LoadAccess = cast<MemoryUse>(MSSA.getMemoryAccess(LoadInst));
+  MemoryDef *StoreAccess = cast<MemoryDef>(MSSA.getMemoryAccess(StoreInst));
+  MemoryAccess *DefiningAccess = LoadAccess->getDefiningAccess();
+  EXPECT_TRUE(isa<MemoryPhi>(DefiningAccess));
+  // Kill the store
+  MSSA.removeMemoryAccess(StoreAccess);
+  MemoryPhi *MP = cast<MemoryPhi>(DefiningAccess);
+  // Verify the phi ended up as liveonentry, liveonentry
+  for (auto &Op : MP->incoming_values())
+    EXPECT_TRUE(MSSA.isLiveOnEntryDef(cast<MemoryAccess>(Op.get())));
+  // Replace the phi uses with the live on entry def
+  MP->replaceAllUsesWith(MSSA.getLiveOnEntryDef());
+  // Verify the load is now defined by liveOnEntryDef
+  EXPECT_TRUE(MSSA.isLiveOnEntryDef(LoadAccess->getDefiningAccess()));
+  // Remove the PHI
+  MSSA.removeMemoryAccess(MP);
+  MSSA.verifyMemorySSA();
+}
+
 TEST_F(MemorySSATest, RemoveMemoryAccess) {
   // We create a diamond where there is a store on one side, and then a load
   // after the merge point.  This enables us to test a bunch of different
   // removal cases.
   F = Function::Create(
       FunctionType::get(B.getVoidTy(), {B.getInt8PtrTy()}, false),
       GlobalValue::ExternalLinkage, "F", &M);
   BasicBlock *Entry(BasicBlock::Create(C, "", F));

 // ; 1 = MemoryDef(liveOnEntry)
 //   store i8 0, i8* %A
 // ; 2 = MemoryDef(1)
 //   store i8 1, i8* %A
 // ; 3 = MemoryDef(2)
 //   store i8 2, i8* %A
 // }
 TEST_F(MemorySSATest, TestTripleStore) {
-  F = Function::Create(
-      FunctionType::get(B.getVoidTy(), {}, false),
+  F = Function::Create(FunctionType::get(B.getVoidTy(), {}, false),
                        GlobalValue::ExternalLinkage, "F", &M);
   B.SetInsertPoint(BasicBlock::Create(C, "", F));
   Type *Int8 = Type::getInt8Ty(C);
   Value *Alloca = B.CreateAlloca(Int8, ConstantInt::get(Int8, 1), "A");
   StoreInst *S1 = B.CreateStore(ConstantInt::get(Int8, 0), Alloca);
   StoreInst *S2 = B.CreateStore(ConstantInt::get(Int8, 1), Alloca);
   StoreInst *S3 = B.CreateStore(ConstantInt::get(Int8, 2), Alloca);
 
   setupAnalyses();
TEST_F(MemorySSATest, TestTripleStore) {
   }
 }
 
 // ...And fixing the above bug made it obvious that, when walking, MemorySSA's
 // walker was caching the initial node it walked. This was fine (albeit
 // mostly redundant) unless the initial node being walked is a clobber for the
 // query. In that case, we'd cache that the node clobbered itself.
 TEST_F(MemorySSATest, TestStoreAndLoad) {
-  F = Function::Create(
-      FunctionType::get(B.getVoidTy(), {}, false),
+  F = Function::Create(FunctionType::get(B.getVoidTy(), {}, false),
                        GlobalValue::ExternalLinkage, "F", &M);
   B.SetInsertPoint(BasicBlock::Create(C, "", F));
   Type *Int8 = Type::getInt8Ty(C);
   Value *Alloca = B.CreateAlloca(Int8, ConstantInt::get(Int8, 1), "A");
   Instruction *SI = B.CreateStore(ConstantInt::get(Int8, 0), Alloca);
   Instruction *LI = B.CreateLoad(Alloca);
 
   setupAnalyses();
   MemorySSA &MSSA = Analyses->MSSA;

 // ...A query to getClobberingMemoryAccess(MemoryAccess*, MemoryLocation) would
 // hand back the store (correctly). A later call to
 // getClobberingMemoryAccess(const Instruction*) would also hand back the store
 // (incorrectly; it should return liveOnEntry).
 //
 // This test checks that repeated calls to either function returns what they're
 // meant to.
 TEST_F(MemorySSATest, TestStoreDoubleQuery) {
-  F = Function::Create(
-      FunctionType::get(B.getVoidTy(), {}, false),
+  F = Function::Create(FunctionType::get(B.getVoidTy(), {}, false),
                        GlobalValue::ExternalLinkage, "F", &M);
   B.SetInsertPoint(BasicBlock::Create(C, "", F));
   Type *Int8 = Type::getInt8Ty(C);
   Value *Alloca = B.CreateAlloca(Int8, ConstantInt::get(Int8, 1), "A");
   StoreInst *SI = B.CreateStore(ConstantInt::get(Int8, 0), Alloca);
 
   setupAnalyses();
   MemorySSA &MSSA = Analyses->MSSA;
   MemorySSAWalker *Walker = Analyses->Walker;
 
   MemoryAccess *StoreAccess = MSSA.getMemoryAccess(SI);
   MemoryLocation StoreLoc = MemoryLocation::get(SI);
-  MemoryAccess *Clobber = Walker->getClobberingMemoryAccess(StoreAccess, StoreLoc);
+  MemoryAccess *Clobber =
+      Walker->getClobberingMemoryAccess(StoreAccess, StoreLoc);
   MemoryAccess *LiveOnEntry = Walker->getClobberingMemoryAccess(SI);
 
   EXPECT_EQ(Clobber, StoreAccess);
   EXPECT_TRUE(MSSA.isLiveOnEntryDef(LiveOnEntry));
 
   // Try again (with entries in the cache already) for good measure...
   Clobber = Walker->getClobberingMemoryAccess(StoreAccess, StoreLoc);
   LiveOnEntry = Walker->getClobberingMemoryAccess(SI);
   EXPECT_EQ(Clobber, StoreAccess);
   EXPECT_TRUE(MSSA.isLiveOnEntryDef(LiveOnEntry));
 }