[AA] Split up LocationSize::unknown()

[nikic]

Summary

Currently, we have some confusion in the codebase regarding the meaning of LocationSize::unknown(): Some parts (including most of BasicAA) assume that LocationSize::unknown() only allows accesses after the base pointer. Some parts (various callers of AA) assume that LocationSize::unknown() allows accesses both before and after the base pointer (but within the underlying object).

This patch splits up LocationSize::unknown() into LocationSize::afterPointer() and LocationSize::beforeOrAfterPointer() to make this completely unambiguous. I tried my best to determine which one is appropriate for all the existing uses.

The test changes in cs-cs.ll in particular illustrate a previously clearly incorrect AA result: We were effectively assuming that argmemonly functions were only allowed to access their arguments after the passed pointer, but not before it. I'm pretty sure that this was not intentional, and it's certainly not specified by LangRef that way.

[asbirlea]

• LocationSize::unknownMaybeNegative() seems somewhat ambiguous in isolation; unless I see the other name or have the context from this patch. I'm either keep LocationSize::unknown or make it even more verbose LocationSize::unknownPositiveOrNegative(). I think the most restrictive case ( LocationSize::unknownMaybeNegative() or renamed version) should be the default ~uint64_t(0), but don't feel strongly about it.
• clang-format

llvm/include/llvm/Analysis/MemoryLocation.h

286

Default to the most generic? unknownMaybeNegative

llvm/lib/Analysis/BasicAliasAnalysis.cpp

1340–1341

Could you clarify the TODO?

1592

This is not unknownMaybeNegative() because of the above check !cast<ConstantInt>(PVGEP->idx_begin())->isNegative() ?

I would set this to unknownMaybeNegative() and leave the TODO.

llvm/lib/Analysis/LoopAccessAnalysis.cpp

517

For checks in loops using AST, I'd use LocationSize::unknownMaybeNegative().

[jdoerfert]

The test changes in cs-cs.ll in particular illustrate a previously clearly incorrect AA result: We were effectively assuming that argmemonly functions were only allowed to access their arguments after the passed pointer, but not before it. I'm pretty sure that this was not intentional, and it's certainly not specified by LangRef that way.

I haven't looked at the patch yet but I agree with this.

[nikic]

In D91649#2401252, @asbirlea wrote:

• LocationSize::unknownMaybeNegative() seems somewhat ambiguous in isolation; unless I see the other name or have the context from this patch. I'm either keep LocationSize::unknown or make it even more verbose LocationSize::unknownPositiveOrNegative().

I'd like to not reuse the existing unknown() name, to force all users (including out of tree users) to make a decision one way or another. Not particularly attached to the names though. We could also drop the "unknown" prefix and make them LocationSize::nonNegative() and LocationSize::positiveOrNegative() for example.

Generally I'm not really fond of "negative" sizes as a concept, it just seemed like the most concise way to explain it. It would be more accurate to say that the size is always positive, but there may be a negative offset. So maybe LocationSize::nonNegative(), LocationSize::withNonNegativeOffset() and LocationSize::withAnyOffset(), where the first two are aliases but can be used according to desired semantics. Can't say I really like this either though.

Or maybe LocationSize::afterPointer() and LocationSize::beforeOrAfterPointer().

[asbirlea]

In D91649#2401902, @nikic wrote:

In D91649#2401252, @asbirlea wrote:

• LocationSize::unknownMaybeNegative() seems somewhat ambiguous in isolation; unless I see the other name or have the context from this patch. I'm either keep LocationSize::unknown or make it even more verbose LocationSize::unknownPositiveOrNegative().

I'd like to not reuse the existing unknown() name, to force all users (including out of tree users) to make a decision one way or another. Not particularly attached to the names though. We could also drop the "unknown" prefix and make them LocationSize::nonNegative() and LocationSize::positiveOrNegative() for example.

Generally I'm not really fond of "negative" sizes as a concept, it just seemed like the most concise way to explain it. It would be more accurate to say that the size is always positive, but there may be a negative offset. So maybe LocationSize::nonNegative(), LocationSize::withNonNegativeOffset() and LocationSize::withAnyOffset(), where the first two are aliases but can be used according to desired semantics. Can't say I really like this either though.

Or maybe LocationSize::afterPointer() and LocationSize::beforeOrAfterPointer().

Either of the options: LocationSize::withNonNegativeOffset() and LocationSize::withAnyOffset(), or LocationSize::afterPointer() and LocationSize::beforeOrAfterPointer()` are better IMO.
I don't have strong opinions either way as long as they're reasonably self explanatory, and these meet that criteria.

[nikic]

Rebase, address review.

Add MemoryLocation::getBasedOn() and MemoryLocation::getStartingFrom() helpers.

Still unsure about the naming for the LocationSize method.

[nikic]

llvm/include/llvm/Analysis/MemoryLocation.h

286

I have dropped this default entirely in https://github.com/llvm/llvm-project/commit/393b9e9db31a3f83bc8b813ee24b56bc8ed93a49. We should not assume one way or another.

llvm/lib/Analysis/BasicAliasAnalysis.cpp

1340–1341

This TODO is for D91482. I've just dropped the TODO entirely as I committed the hasValue() usage separately.

1592

That's right, I've expanded the TODO a bit. I think we should leave this at unknownNonNegative() for now, as changing it to unknownMaybeNegative() might technically regress results, so it seems like something to evaluate separately.

llvm/lib/Analysis/LoopAccessAnalysis.cpp

517

From cursory inspection, I didn't see any obvious requirement that the loads be increasing, so I agree that this should use unknownMaybeNegative().

[nikic]

Rename to LocationSize::afterPointer() and LocationSize::beforeOrAfterPointer().

[nikic]

Rename the MemoryLocation helpers as well. With the new LocationSize naming, it makes sense to call these MemoryLocation::getAfter() and MemoryLocation::getBeforeOrAfter().

[nikic]

Accept AATags in MemoryLocation::getAfter/getBeforeOrAfter helpers, which makes them usable in more cases.

[asbirlea]

One more comment, the others look good.

llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp

290

getBeforeOrAfter?

[nikic]

llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp

290

If I'm understanding the context here right, this function only deals with accesses for which hasAnalyzableMemoryWrite() returns true, i.e. strcpy, strncpy, strcat and strncat in this branch. These functions don't access memory before the passed pointer.

[asbirlea]

lgtm.
Please wait in case fhahn@ has additional comments.

[fhahn]

This looks like a great improvement, thanks!

llvm/lib/Analysis/BasicAliasAnalysis.cpp

1733

nit: may be before instead of may be below, as the function is called mayBeBeforePoitner?

llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp

290

yes, only known TLI functions should reach here.

llvm/include/llvm/Analysis/AliasAnalysis.h

public:
   /// A convenience wrapper around the primary \c alias interface.
   AliasResult alias(const Value *V1, LocationSize V1Size, const Value *V2,
                     LocationSize V2Size) {
     return alias(MemoryLocation(V1, V1Size), MemoryLocation(V2, V2Size));
   }
 
   /// A convenience wrapper around the primary \c alias interface.
   AliasResult alias(const Value *V1, const Value *V2) {
-    return alias(V1, LocationSize::unknown(), V2, LocationSize::unknown());
+    return alias(MemoryLocation::getBeforeOrAfter(V1),
+                 MemoryLocation::getBeforeOrAfter(V2));
   }
 
   /// A trivial helper function to check to see if the specified pointers are
   /// no-alias.
   bool isNoAlias(const MemoryLocation &LocA, const MemoryLocation &LocB) {
     return alias(LocA, LocB) == NoAlias;
   }
 
   /// A convenience wrapper around the \c isNoAlias helper interface.
   bool isNoAlias(const Value *V1, LocationSize V1Size, const Value *V2,
                  LocationSize V2Size) {
     return isNoAlias(MemoryLocation(V1, V1Size), MemoryLocation(V2, V2Size));
   }
 
   /// A convenience wrapper around the \c isNoAlias helper interface.
   bool isNoAlias(const Value *V1, const Value *V2) {
-    return isNoAlias(MemoryLocation(V1, LocationSize::unknown()),
-                     MemoryLocation(V2, LocationSize::unknown()));
+    return isNoAlias(MemoryLocation::getBeforeOrAfter(V1),
+                     MemoryLocation::getBeforeOrAfter(V2));
   }
 
   /// A trivial helper function to check to see if the specified pointers are
   /// must-alias.
   bool isMustAlias(const MemoryLocation &LocA, const MemoryLocation &LocB) {
     return alias(LocA, LocB) == MustAlias;
   }
 
   /// A convenience wrapper around the \c isMustAlias helper interface.
   bool isMustAlias(const Value *V1, const Value *V2) {
     return alias(V1, LocationSize::precise(1), V2, LocationSize::precise(1)) ==
            MustAlias;
   }
 
   /// Checks whether the given location points to constant memory, or if
   /// \p OrLocal is true whether it points to a local alloca.
   bool pointsToConstantMemory(const MemoryLocation &Loc, bool OrLocal = false);
 
   /// A convenience wrapper around the primary \c pointsToConstantMemory
   /// interface.
   bool pointsToConstantMemory(const Value *P, bool OrLocal = false) {
-    return pointsToConstantMemory(MemoryLocation(P, LocationSize::unknown()),
-                                  OrLocal);
+    return pointsToConstantMemory(MemoryLocation::getBeforeOrAfter(P), OrLocal);
   }
 
   /// @}
   //===--------------------------------------------------------------------===//
   /// \name Simple mod/ref information
   /// @{
 
   /// Get the ModRef info associated with a pointer argument of a call. The

llvm/include/llvm/Analysis/MemoryDependenceAnalysis.h

private:
   struct NonLocalPointerInfo {
     /// The pair of the block and the skip-first-block flag.
     BBSkipFirstBlockPair Pair;
     /// The results of the query for each relevant block.
     NonLocalDepInfo NonLocalDeps;
     /// The maximum size of the dereferences of the pointer.
     ///
     /// May be UnknownSize if the sizes are unknown.
-    LocationSize Size = LocationSize::unknown();
+    LocationSize Size = LocationSize::afterPointer();
     /// The AA tags associated with dereferences of the pointer.
     ///
     /// The members may be null if there are no tags or conflicting tags.
     AAMDNodes AATags;
 
     NonLocalPointerInfo() = default;
   };
 

llvm/include/llvm/Analysis/MemoryLocation.h

 //
 // ...Since we'll copy *up to* 4 bytes into %p, but we can't guarantee that
 // we'll ever actually do so.
 //
 // If asked to represent a pathologically large value, this will degrade to
 // None.
 class LocationSize {
   enum : uint64_t {
-    Unknown = ~uint64_t(0),
+    BeforeOrAfterPointer = ~uint64_t(0),
+    AfterPointer = BeforeOrAfterPointer - 1,
+    MapEmpty = BeforeOrAfterPointer - 2,
+    MapTombstone = BeforeOrAfterPointer - 3,
     ImpreciseBit = uint64_t(1) << 63,
-    MapEmpty = Unknown - 1,
-    MapTombstone = Unknown - 2,
 
     // The maximum value we can represent without falling back to 'unknown'.
     MaxValue = (MapTombstone - 1) & ~ImpreciseBit,
   };
 
   uint64_t Value;
 
   // Hack to support implicit construction. This should disappear when the
   // public LocationSize ctor goes away.
   enum DirectConstruction { Direct };
 
   constexpr LocationSize(uint64_t Raw, DirectConstruction): Value(Raw) {}
 
-  static_assert(Unknown & ImpreciseBit, "Unknown is imprecise by definition.");
+  static_assert(AfterPointer & ImpreciseBit,
+                "AfterPointer is imprecise by definition.");
+  static_assert(BeforeOrAfterPointer & ImpreciseBit,
+                "BeforeOrAfterPointer is imprecise by definition.");
+
 public:
   // FIXME: Migrate all users to construct via either `precise` or `upperBound`,
   // to make it more obvious at the callsite the kind of size that they're
   // providing.
   //
   // Since the overwhelming majority of users of this provide precise values,
   // this assumes the provided value is precise.
   constexpr LocationSize(uint64_t Raw)
-      : Value(Raw > MaxValue ? Unknown : Raw) {}
+      : Value(Raw > MaxValue ? AfterPointer : Raw) {}
 
   static LocationSize precise(uint64_t Value) { return LocationSize(Value); }
   static LocationSize precise(TypeSize Value) {
     if (Value.isScalable())
-      return unknown();
+      return afterPointer();
     return precise(Value.getFixedSize());
   }
 
   static LocationSize upperBound(uint64_t Value) {
     // You can't go lower than 0, so give a precise result.
     if (LLVM_UNLIKELY(Value == 0))
       return precise(0);
     if (LLVM_UNLIKELY(Value > MaxValue))
-      return unknown();
+      return afterPointer();
     return LocationSize(Value | ImpreciseBit, Direct);
   }
   static LocationSize upperBound(TypeSize Value) {
     if (Value.isScalable())
-      return unknown();
+      return afterPointer();
     return upperBound(Value.getFixedSize());
   }
 
-  constexpr static LocationSize unknown() {
-    return LocationSize(Unknown, Direct);
+  /// Any location after the base pointer (but still within the underlying
+  /// object).
+  constexpr static LocationSize afterPointer() {
+    return LocationSize(AfterPointer, Direct);
+  }
+
+  /// Any location before or after the base pointer (but still within the
+  /// underlying object).
+  constexpr static LocationSize beforeOrAfterPointer() {
+    return LocationSize(BeforeOrAfterPointer, Direct);
   }
 
   // Sentinel values, generally used for maps.
   constexpr static LocationSize mapTombstone() {
     return LocationSize(MapTombstone, Direct);
   }
   constexpr static LocationSize mapEmpty() {
     return LocationSize(MapEmpty, Direct);
   }
 
   // Returns a LocationSize that can correctly represent either `*this` or
   // `Other`.
   LocationSize unionWith(LocationSize Other) const {
     if (Other == *this)
       return *this;
 
-    if (!hasValue() || !Other.hasValue())
-      return unknown();
+    if (Value == BeforeOrAfterPointer || Other.Value == BeforeOrAfterPointer)
+      return beforeOrAfterPointer();
+    if (Value == AfterPointer || Other.Value == AfterPointer)
+      return afterPointer();
 
     return upperBound(std::max(getValue(), Other.getValue()));
   }
 
-  bool hasValue() const { return Value != Unknown; }
+  bool hasValue() const {
+    return Value != AfterPointer && Value != BeforeOrAfterPointer;
+  }
   uint64_t getValue() const {
     assert(hasValue() && "Getting value from an unknown LocationSize!");
     return Value & ~ImpreciseBit;
   }
 
   // Returns whether or not this value is precise. Note that if a value is
-  // precise, it's guaranteed to not be `unknown()`.
+  // precise, it's guaranteed to not be unknown.
   bool isPrecise() const {
     return (Value & ImpreciseBit) == 0;
   }
 
   // Convenience method to check if this LocationSize's value is 0.
   bool isZero() const { return hasValue() && getValue() == 0; }
 
+  /// Whether accesses before the base pointer are possible.
+  bool mayBeBeforePointer() const { return Value == BeforeOrAfterPointer; }
+
   bool operator==(const LocationSize &Other) const {
     return Value == Other.Value;
   }
 
   bool operator!=(const LocationSize &Other) const {
     return !(*this == Other);
   }
 
public:
   /// Return a location representing a particular argument of a call.
   static MemoryLocation getForArgument(const CallBase *Call, unsigned ArgIdx,
                                        const TargetLibraryInfo *TLI);
   static MemoryLocation getForArgument(const CallBase *Call, unsigned ArgIdx,
                                        const TargetLibraryInfo &TLI) {
     return getForArgument(Call, ArgIdx, &TLI);
   }
 
+  /// Return a location that may access any location after Ptr, while remaining
+  /// within the underlying object.
+  static MemoryLocation getAfter(const Value *Ptr,
+                                 const AAMDNodes &AATags = AAMDNodes()) {
+    return MemoryLocation(Ptr, LocationSize::afterPointer(), AATags);
+  }
+
+  /// Return a location that may access any location before or after Ptr, while
+  /// remaining within the underlying object.
+  static MemoryLocation
+  getBeforeOrAfter(const Value *Ptr, const AAMDNodes &AATags = AAMDNodes()) {
+    return MemoryLocation(Ptr, LocationSize::beforeOrAfterPointer(), AATags);
+  }
+
   // Return the exact size if the exact size is known at compiletime,
   // otherwise return MemoryLocation::UnknownSize.
   static uint64_t getSizeOrUnknown(const TypeSize &T) {
     return T.isScalable() ? UnknownSize : T.getFixedSize();
   }
 
-  MemoryLocation() : Ptr(nullptr), Size(LocationSize::unknown()), AATags() {}
+  MemoryLocation()
+      : Ptr(nullptr), Size(LocationSize::beforeOrAfterPointer()), AATags() {}
 
   explicit MemoryLocation(const Value *Ptr, LocationSize Size,
                           const AAMDNodes &AATags = AAMDNodes())
       : Ptr(Ptr), Size(Size), AATags(AATags) {}
 
   MemoryLocation getWithNewPtr(const Value *NewPtr) const {
     MemoryLocation Copy(*this);
     Copy.Ptr = NewPtr;

llvm/include/llvm/Analysis/MemorySSA.h

void fillInCurrentPair() {
     if (WalkingPhi && Location.Ptr) {
       // Mark size as unknown, if the location is not guaranteed to be
       // loop-invariant for any possible loop in the function. Setting the size
       // to unknown guarantees that any memory accesses that access locations
       // after the pointer are considered as clobbers, which is important to
       // catch loop carried dependences.
       if (Location.Ptr &&
           !IsGuaranteedLoopInvariant(const_cast<Value *>(Location.Ptr)))
-        CurrentPair.second = Location.getWithNewSize(LocationSize::unknown());
+        CurrentPair.second =
+            Location.getWithNewSize(LocationSize::beforeOrAfterPointer());
       PHITransAddr Translator(
           const_cast<Value *>(Location.Ptr),
           OriginalAccess->getBlock()->getModule()->getDataLayout(), nullptr);
 
       if (!Translator.PHITranslateValue(OriginalAccess->getBlock(),
                                         DefIterator.getPhiArgBlock(), DT,
                                         true)) {
         Value *TransAddr = Translator.getAddr();
         if (TransAddr != Location.Ptr) {
           CurrentPair.second = CurrentPair.second.getWithNewPtr(TransAddr);
 
           if (TransAddr &&
               !IsGuaranteedLoopInvariant(const_cast<Value *>(TransAddr)))
-            CurrentPair.second =
-                CurrentPair.second.getWithNewSize(LocationSize::unknown());
+            CurrentPair.second = CurrentPair.second.getWithNewSize(
+                LocationSize::beforeOrAfterPointer());
 
           if (PerformedPhiTranslation)
             *PerformedPhiTranslation = true;
         }
       }
     }
   }
 

llvm/include/llvm/LinkAllPasses.h

ForcePassLinking() {
       (void)new llvm::IntervalPartition();
       (void)new llvm::ScalarEvolutionWrapperPass();
       llvm::Function::Create(nullptr, llvm::GlobalValue::ExternalLinkage)->viewCFGOnly();
       llvm::RGPassManager RGM;
       llvm::TargetLibraryInfoImpl TLII;
       llvm::TargetLibraryInfo TLI(TLII);
       llvm::AliasAnalysis AA(TLI);
       llvm::AliasSetTracker X(AA);
-      X.add(nullptr, llvm::LocationSize::unknown(),
+      X.add(nullptr, llvm::LocationSize::beforeOrAfterPointer(),
             llvm::AAMDNodes()); // for -print-alias-sets
       (void) llvm::AreStatisticsEnabled();
       (void) llvm::sys::RunningOnValgrind();
     }
   } ForcePassLinking; // Force link by creating a global definition.
 }
 
 #endif

llvm/lib/Analysis/AliasAnalysisEvaluator.cpp

void AAEvaluator::runInternal(Function &F, AAResults &AA) {
   if (PrintAll || PrintNoAlias || PrintMayAlias || PrintPartialAlias ||
       PrintMustAlias || PrintNoModRef || PrintMod || PrintRef || PrintModRef)
     errs() << "Function: " << F.getName() << ": " << Pointers.size()
            << " pointers, " << Calls.size() << " call sites\n";
 
   // iterate over the worklist, and run the full (n^2)/2 disambiguations
   for (SetVector<Value *>::iterator I1 = Pointers.begin(), E = Pointers.end();
        I1 != E; ++I1) {
-    auto I1Size = LocationSize::unknown();
+    auto I1Size = LocationSize::afterPointer();
     Type *I1ElTy = cast<PointerType>((*I1)->getType())->getElementType();
     if (I1ElTy->isSized())
       I1Size = LocationSize::precise(DL.getTypeStoreSize(I1ElTy));
 
     for (SetVector<Value *>::iterator I2 = Pointers.begin(); I2 != I1; ++I2) {
-      auto I2Size = LocationSize::unknown();
+      auto I2Size = LocationSize::afterPointer();
       Type *I2ElTy = cast<PointerType>((*I2)->getType())->getElementType();
       if (I2ElTy->isSized())
         I2Size = LocationSize::precise(DL.getTypeStoreSize(I2ElTy));
 
       AliasResult AR = AA.alias(*I1, I1Size, *I2, I2Size);
       switch (AR) {
       case NoAlias:
         PrintResults(AR, PrintNoAlias, *I1, *I2, F.getParent());
for (SetVector<Value *>::iterator I1 = Stores.begin(), E = Stores.end();
         }
       }
     }
   }
 
   // Mod/ref alias analysis: compare all pairs of calls and values
   for (CallBase *Call : Calls) {
     for (auto Pointer : Pointers) {
-      auto Size = LocationSize::unknown();
+      auto Size = LocationSize::afterPointer();
       Type *ElTy = cast<PointerType>(Pointer->getType())->getElementType();
       if (ElTy->isSized())
         Size = LocationSize::precise(DL.getTypeStoreSize(ElTy));
 
       switch (AA.getModRefInfo(Call, Pointer, Size)) {
       case ModRefInfo::NoModRef:
         PrintModRefResults("NoModRef", PrintNoModRef, Call, Pointer,
                            F.getParent());

llvm/lib/Analysis/AliasSetTracker.cpp

void AliasSet::print(raw_ostream &OS) const {
   if (Forward)
     OS << " forwarding to " << (void*)Forward;
 
   if (!empty()) {
     OS << "Pointers: ";
     for (iterator I = begin(), E = end(); I != E; ++I) {
       if (I != begin()) OS << ", ";
       I.getPointer()->printAsOperand(OS << "(");
-      if (I.getSize() == LocationSize::unknown())
-        OS << ", unknown)";
+      if (I.getSize() == LocationSize::afterPointer())
+        OS << ", unknown after)";
+      else if (I.getSize() == LocationSize::beforeOrAfterPointer())
+        OS << ", unknown before-or-after)";
       else
         OS << ", " << I.getSize() << ")";
     }
   }
   if (!UnknownInsts.empty()) {
     OS << "\n    " << UnknownInsts.size() << " Unknown instructions: ";
     for (unsigned i = 0, e = UnknownInsts.size(); i != e; ++i) {
       if (i) OS << ", ";

llvm/lib/Analysis/BasicAliasAnalysis.cpp

for (auto CI = Call->data_operands_begin(), CE = Call->data_operands_end();
       // Call doesn't access memory through this operand, so we don't care
       // if it aliases with Object.
       if (Call->doesNotAccessMemory(OperandNo))
         continue;
 
       // If this is a no-capture pointer argument, see if we can tell that it
       // is impossible to alias the pointer we're checking.
       AliasResult AR = getBestAAResults().alias(
-          MemoryLocation(*CI, LocationSize::unknown()),
-          MemoryLocation(Object, LocationSize::unknown()), AAQI);
+          MemoryLocation::getBeforeOrAfter(*CI),
+          MemoryLocation::getBeforeOrAfter(Object), AAQI);
       if (AR != MustAlias)
         IsMustAlias = false;
       // Operand doesn't alias 'Object', continue looking for other aliases
       if (AR == NoAlias)
         continue;
       // Operand aliases 'Object', but call doesn't modify it. Strengthen
       // initial assumption and keep looking in case if there are more aliases.
       if (Call->onlyReadsMemory(OperandNo)) {
ModRefInfo BasicAAResult::getModRefInfo(const CallBase *Call,
   // modify any IR visible value.  This is only valid because we assume these
   // routines do not read values visible in the IR.  TODO: Consider special
   // casing realloc and strdup routines which access only their arguments as
   // well.  Or alternatively, replace all of this with inaccessiblememonly once
   // that's implemented fully.
   if (isMallocOrCallocLikeFn(Call, &TLI)) {
     // Be conservative if the accessed pointer may alias the allocation -
     // fallback to the generic handling below.
-    if (getBestAAResults().alias(MemoryLocation(Call, LocationSize::unknown()),
+    if (getBestAAResults().alias(MemoryLocation::getBeforeOrAfter(Call),
                                  Loc, AAQI) == NoAlias)
       return ModRefInfo::NoModRef;
   }
 
   // The semantics of memcpy intrinsics either exactly overlap or do not
   // overlap, i.e., source and destination of any given memcpy are either
   // no-alias or must-alias.
   if (auto *Inst = dyn_cast<AnyMemCpyInst>(Call)) {
AliasResult BasicAAResult::aliasGEP(
   // pointers, figure out if the indexes to the GEP tell us anything about the
   // derived pointer.
   if (const GEPOperator *GEP2 = dyn_cast<GEPOperator>(V2)) {
     // Check for the GEP base being at a negative offset, this time in the other
     // direction.
     if (isGEPBaseAtNegativeOffset(GEP2, DecompGEP2, DecompGEP1, V1Size))
       return NoAlias;
     // Do the base pointers alias?
-    AliasResult BaseAlias =
-        aliasCheck(UnderlyingV1, LocationSize::unknown(), AAMDNodes(),
-                   UnderlyingV2, LocationSize::unknown(), AAMDNodes(), AAQI);
+    AliasResult BaseAlias = aliasCheck(
+        UnderlyingV1, LocationSize::beforeOrAfterPointer(), AAMDNodes(),
+        UnderlyingV2, LocationSize::beforeOrAfterPointer(), AAMDNodes(), AAQI);
 
     // For GEPs with identical offsets, we can preserve the size and AAInfo
     // when performing the alias check on the underlying objects.
     if (BaseAlias == MayAlias && DecompGEP1.Offset == DecompGEP2.Offset &&
         DecompGEP1.VarIndices == DecompGEP2.VarIndices) {
       AliasResult PreciseBaseAlias = aliasCheck(
           UnderlyingV1, V1Size, V1AAInfo, UnderlyingV2, V2Size, V2AAInfo, AAQI);
       if (PreciseBaseAlias == NoAlias)
if (const GEPOperator *GEP2 = dyn_cast<GEPOperator>(V2)) {
     // Check to see if these two pointers are related by the getelementptr
     // instruction.  If one pointer is a GEP with a non-zero index of the other
     // pointer, we know they cannot alias.
 
     // If both accesses are unknown size, we can't do anything useful here.
     if (!V1Size.hasValue() && !V2Size.hasValue())
       return MayAlias;
 
-    AliasResult R = aliasCheck(UnderlyingV1, LocationSize::unknown(),
-                               AAMDNodes(), V2, LocationSize::unknown(),
-                               V2AAInfo, AAQI, nullptr, UnderlyingV2);
+    AliasResult R = aliasCheck(
+        UnderlyingV1, LocationSize::beforeOrAfterPointer(), AAMDNodes(),
+        V2, V2Size, V2AAInfo, AAQI, nullptr, UnderlyingV2);
     if (R != MustAlias) {
       // If V2 may alias GEP base pointer, conservatively returns MayAlias.
       // If V2 is known not to alias GEP base pointer, then the two values
       // cannot alias per GEP semantics: "Any memory access must be done through
       // a pointer value associated with an address range of the memory access,
       // otherwise the behavior is undefined.".
       assert(R == NoAlias || R == MayAlias);
       return R;
if (DecompGEP1.Offset != 0 && DecompGEP1.VarIndices.empty()) {
     } else {
       // We have the situation where:
       // +                +
       // | BaseOffset     |
       // ---------------->|
       // |-->V1Size       |-------> V2Size
       // GEP1             V2
       // We need to know that V2Size is not unknown, otherwise we might have
       // stripped a gep with negative index ('gep <ptr>, -1, ...).
       if (V1Size.hasValue() && V2Size.hasValue()) {
         if ((-DecompGEP1.Offset).ult(V1Size.getValue()))
           return PartialAlias;
         return NoAlias;
       }
     }
   }
 
   if (!DecompGEP1.VarIndices.empty()) {
AliasResult BasicAAResult::aliasPHI(const PHINode *PN, LocationSize PNSize,
   // block, but return MayAlias just in case.
   if (V1Srcs.empty())
     return MayAlias;
 
   // If this PHI node is recursive, set the size of the accessed memory to
   // unknown to represent all the possible values the GEP could advance the
   // pointer to.
   if (isRecursive)
-    PNSize = LocationSize::unknown();
+    // TODO: We are checking above that the addrec GEP has a positive offset
+    // and can thus assume that all accesses happen after the base pointer.
+    // It might be better to drop the offset requirement and use
+    // beforeOrAfterPointer().
+    PNSize = LocationSize::afterPointer();
 
   // In the recursive alias queries below, we may compare values from two
   // different loop iterations. Keep track of visited phi blocks, which will
   // be used when determining value equivalence.
   bool BlockInserted = VisitedPhiBBs.insert(PN->getParent()).second;
   auto _ = make_scope_exit([&]() {
     if (BlockInserted)
       VisitedPhiBBs.erase(PN->getParent());
AliasResult BasicAAResult::aliasCheck(const Value *V1, LocationSize V1Size,
   if ((isObjectSmallerThan(
           O2, getMinimalExtentFrom(*V1, V1Size, DL, NullIsValidLocation), DL,
           TLI, NullIsValidLocation)) ||
       (isObjectSmallerThan(
           O1, getMinimalExtentFrom(*V2, V2Size, DL, NullIsValidLocation), DL,
           TLI, NullIsValidLocation)))
     return NoAlias;
 
+  // If one the accesses may be before the accessed pointer, canonicalize this
+  // by using unknown after-pointer sizes for both accesses. This is
+  // equivalent, because regardless of which pointer is lower, one of them
+  // will always came after the other, as long as the underlying objects aren't
+  // disjoint. We do this so that the rest of BasicAA does not have to deal
+  // with accesses before the base pointer, and to improve cache utilization by
+  // merging equivalent states.
+  if (V1Size.mayBeBeforePointer() || V2Size.mayBeBeforePointer()) {
+    V1Size = LocationSize::afterPointer();
+    V2Size = LocationSize::afterPointer();
+  }
+
   // Check the cache before climbing up use-def chains. This also terminates
   // otherwise infinitely recursive queries.
   AAQueryInfo::LocPair Locs(MemoryLocation(V1, V1Size, V1AAInfo),
                             MemoryLocation(V2, V2Size, V2AAInfo));
   if (V1 > V2)
     std::swap(Locs.first, Locs.second);
   std::pair<AAQueryInfo::AliasCacheT::iterator, bool> Pair =
       AAQI.AliasCache.try_emplace(Locs, MayAlias);

llvm/lib/Analysis/DependenceAnalysis.cpp

 // Otherwise the underlying objects are checked to see if they point to
 // different identifiable objects.
 static AliasResult underlyingObjectsAlias(AAResults *AA,
                                           const DataLayout &DL,
                                           const MemoryLocation &LocA,
                                           const MemoryLocation &LocB) {
   // Check the original locations (minus size) for noalias, which can happen for
   // tbaa, incompatible underlying object locations, etc.
-  MemoryLocation LocAS(LocA.Ptr, LocationSize::unknown(), LocA.AATags);
-  MemoryLocation LocBS(LocB.Ptr, LocationSize::unknown(), LocB.AATags);
+  MemoryLocation LocAS =
+      MemoryLocation::getBeforeOrAfter(LocA.Ptr, LocA.AATags);
+  MemoryLocation LocBS =
+      MemoryLocation::getBeforeOrAfter(LocB.Ptr, LocB.AATags);
   if (AA->alias(LocAS, LocBS) == NoAlias)
     return NoAlias;
 
   // Check the underlying objects are the same
   const Value *AObj = getUnderlyingObject(LocA.Ptr);
   const Value *BObj = getUnderlyingObject(LocB.Ptr);
 
   // If the underlying objects are the same, they must alias

llvm/lib/Analysis/GlobalsModRef.cpp

ModRefInfo GlobalsAAResult::getModRefInfoForArgument(const CallBase *Call,
   for (auto &A : Call->args()) {
     SmallVector<const Value*, 4> Objects;
     getUnderlyingObjects(A, Objects);
 
     // All objects must be identified.
     if (!all_of(Objects, isIdentifiedObject) &&
         // Try ::alias to see if all objects are known not to alias GV.
         !all_of(Objects, [&](const Value *V) {
-          return this->alias(MemoryLocation(V, LocationSize::unknown()),
-                             MemoryLocation(GV, LocationSize::unknown()),
+          return this->alias(MemoryLocation::getBeforeOrAfter(V),
+                             MemoryLocation::getBeforeOrAfter(GV),
                              AAQI) == NoAlias;
         }))
       return ConservativeResult;
 
     if (is_contained(Objects, GV))
       return ConservativeResult;
   }
 

llvm/lib/Analysis/Lint.cpp

Assert(F.hasName() || F.hasLocalLinkage(),
          "Unusual: Unnamed function with non-local linkage", &F);
 
   // TODO: Check for irreducible control flow.
 }
 
 void Lint::visitCallBase(CallBase &I) {
   Value *Callee = I.getCalledOperand();
 
-  visitMemoryReference(I, MemoryLocation(Callee, LocationSize::unknown()),
-                       None, nullptr, MemRef::Callee);
+  visitMemoryReference(I, MemoryLocation::getAfter(Callee), None, nullptr,
+                       MemRef::Callee);
 
   if (Function *F = dyn_cast<Function>(findValue(Callee,
                                                  /*OffsetOk=*/false))) {
     Assert(I.getCallingConv() == F->getCallingConv(),
            "Undefined behavior: Caller and callee calling convention differ",
            &I);
 
     FunctionType *FT = F->getFunctionType();
case Intrinsic::memcpy: {
       visitMemoryReference(I, MemoryLocation::getForDest(MCI),
                            MCI->getDestAlign(), nullptr, MemRef::Write);
       visitMemoryReference(I, MemoryLocation::getForSource(MCI),
                            MCI->getSourceAlign(), nullptr, MemRef::Read);
 
       // Check that the memcpy arguments don't overlap. The AliasAnalysis API
       // isn't expressive enough for what we really want to do. Known partial
       // overlap is not distinguished from the case where nothing is known.
-      auto Size = LocationSize::unknown();
+      auto Size = LocationSize::afterPointer();
       if (const ConstantInt *Len =
               dyn_cast<ConstantInt>(findValue(MCI->getLength(),
                                               /*OffsetOk=*/false)))
         if (Len->getValue().isIntN(32))
           Size = LocationSize::precise(Len->getValue().getZExtValue());
       Assert(AA->alias(MCI->getSource(), Size, MCI->getDest(), Size) !=
                  MustAlias,
              "Undefined behavior: memcpy source and destination overlap", &I);

 }
 
 void Lint::visitVAArgInst(VAArgInst &I) {
   visitMemoryReference(I, MemoryLocation::get(&I), None, nullptr,
                        MemRef::Read | MemRef::Write);
 }
 
 void Lint::visitIndirectBrInst(IndirectBrInst &I) {
-  visitMemoryReference(
-      I, MemoryLocation(I.getAddress(), LocationSize::unknown()),
-      None, nullptr, MemRef::Branchee);
+  visitMemoryReference(I, MemoryLocation::getAfter(I.getAddress()), None,
+                       nullptr, MemRef::Branchee);
 
   Assert(I.getNumDestinations() != 0,
          "Undefined behavior: indirectbr with no destinations", &I);
 }
 
 void Lint::visitExtractElementInst(ExtractElementInst &I) {
   if (ConstantInt *CI = dyn_cast<ConstantInt>(findValue(I.getIndexOperand(),
                                                         /*OffsetOk=*/false)))

llvm/lib/Analysis/LoopAccessAnalysis.cpp

AccessAnalysis(Loop *TheLoop, AAResults *AA, LoopInfo *LI,
                  MemoryDepChecker::DepCandidates &DA,
                  PredicatedScalarEvolution &PSE)
       : TheLoop(TheLoop), AST(*AA), LI(LI), DepCands(DA),
         IsRTCheckAnalysisNeeded(false), PSE(PSE) {}
 
   /// Register a load  and whether it is only read from.
   void addLoad(MemoryLocation &Loc, bool IsReadOnly) {
     Value *Ptr = const_cast<Value*>(Loc.Ptr);
-    AST.add(Ptr, LocationSize::unknown(), Loc.AATags);
+    AST.add(Ptr, LocationSize::beforeOrAfterPointer(), Loc.AATags);
     Accesses.insert(MemAccessInfo(Ptr, false));
     if (IsReadOnly)
       ReadOnlyPtr.insert(Ptr);
   }
 
   /// Register a store.
   void addStore(MemoryLocation &Loc) {
     Value *Ptr = const_cast<Value*>(Loc.Ptr);
-    AST.add(Ptr, LocationSize::unknown(), Loc.AATags);
+    AST.add(Ptr, LocationSize::beforeOrAfterPointer(), Loc.AATags);
     Accesses.insert(MemAccessInfo(Ptr, true));
   }
 
   /// Check if we can emit a run-time no-alias check for \p Access.
   ///
   /// Returns true if we can emit a run-time no alias check for \p Access.
   /// If we can check this access, this also adds it to a dependence set and
   /// adds a run-time to check for it to \p RtCheck. If \p Assume is true,

llvm/lib/Analysis/MemoryDependenceAnalysis.cpp

static ModRefInfo GetLocation(const Instruction *Inst, MemoryLocation &Loc,
 
   if (const VAArgInst *V = dyn_cast<VAArgInst>(Inst)) {
     Loc = MemoryLocation::get(V);
     return ModRefInfo::ModRef;
   }
 
   if (const CallInst *CI = isFreeCall(Inst, &TLI)) {
     // calls to free() deallocate the entire structure
-    Loc = MemoryLocation(CI->getArgOperand(0), LocationSize::unknown());
+    Loc = MemoryLocation::getAfter(CI->getArgOperand(0));
     return ModRefInfo::Mod;
   }
 
   if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) {
     switch (II->getIntrinsicID()) {
     case Intrinsic::lifetime_start:
     case Intrinsic::lifetime_end:
     case Intrinsic::invariant_start:
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) {
       // because the value is undefined.
       Intrinsic::ID ID = II->getIntrinsicID();
       switch (ID) {
       case Intrinsic::lifetime_start: {
         // FIXME: This only considers queries directly on the invariant-tagged
         // pointer, not on query pointers that are indexed off of them.  It'd
         // be nice to handle that at some point (the right approach is to use
         // GetPointerBaseWithConstantOffset).
-        MemoryLocation ArgLoc(II->getArgOperand(1), LocationSize::unknown());
+        MemoryLocation ArgLoc = MemoryLocation::getAfter(II->getArgOperand(1));
         if (BatchAA.isMustAlias(ArgLoc, MemLoc))
           return MemDepResult::getDef(II);
         continue;
       }
       case Intrinsic::masked_load:
       case Intrinsic::masked_store: {
         MemoryLocation Loc;
         /*ModRefInfo MR =*/ GetLocation(II, Loc, TLI);

llvm/lib/Analysis/MemoryLocation.cpp

 #include "llvm/IR/IntrinsicsARM.h"
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/IR/Module.h"
 #include "llvm/IR/Type.h"
 using namespace llvm;
 
 void LocationSize::print(raw_ostream &OS) const {
   OS << "LocationSize::";
-  if (*this == unknown())
-    OS << "unknown";
+  if (*this == beforeOrAfterPointer())
+    OS << "beforeOrAfterPointer";
+  if (*this == afterPointer())
+    OS << "afterPointer";
   else if (*this == mapEmpty())
     OS << "mapEmpty";
   else if (*this == mapTombstone())
     OS << "mapTombstone";
   else if (isPrecise())
     OS << "precise(" << getValue() << ')';
   else
     OS << "upperBound(" << getValue() << ')';
return MemoryLocation(SI->getPointerOperand(),
                             SI->getValueOperand()->getType())),
                         AATags);
 }
 
 MemoryLocation MemoryLocation::get(const VAArgInst *VI) {
   AAMDNodes AATags;
   VI->getAAMetadata(AATags);
 
-  return MemoryLocation(VI->getPointerOperand(), LocationSize::unknown(),
-                        AATags);
+  return MemoryLocation(VI->getPointerOperand(),
+                        LocationSize::afterPointer(), AATags);
 }
 
 MemoryLocation MemoryLocation::get(const AtomicCmpXchgInst *CXI) {
   AAMDNodes AATags;
   CXI->getAAMetadata(AATags);
   const auto &DL = CXI->getModule()->getDataLayout();
 
   return MemoryLocation(CXI->getPointerOperand(),
MemoryLocation MemoryLocation::getForSource(const MemTransferInst *MTI) {
   return getForSource(cast<AnyMemTransferInst>(MTI));
 }
 
 MemoryLocation MemoryLocation::getForSource(const AtomicMemTransferInst *MTI) {
   return getForSource(cast<AnyMemTransferInst>(MTI));
 }
 
 MemoryLocation MemoryLocation::getForSource(const AnyMemTransferInst *MTI) {
-  auto Size = LocationSize::unknown();
+  auto Size = LocationSize::afterPointer();
   if (ConstantInt *C = dyn_cast<ConstantInt>(MTI->getLength()))
     Size = LocationSize::precise(C->getValue().getZExtValue());
 
   // memcpy/memmove can have AA tags. For memcpy, they apply
   // to both the source and the destination.
   AAMDNodes AATags;
   MTI->getAAMetadata(AATags);
 
   return MemoryLocation(MTI->getRawSource(), Size, AATags);
 }
 
 MemoryLocation MemoryLocation::getForDest(const MemIntrinsic *MI) {
   return getForDest(cast<AnyMemIntrinsic>(MI));
 }
 
 MemoryLocation MemoryLocation::getForDest(const AtomicMemIntrinsic *MI) {
   return getForDest(cast<AnyMemIntrinsic>(MI));
 }
 
 MemoryLocation MemoryLocation::getForDest(const AnyMemIntrinsic *MI) {
-  auto Size = LocationSize::unknown();
+  auto Size = LocationSize::afterPointer();
   if (ConstantInt *C = dyn_cast<ConstantInt>(MI->getLength()))
     Size = LocationSize::precise(C->getValue().getZExtValue());
 
   // memcpy/memmove can have AA tags. For memcpy, they apply
   // to both the source and the destination.
   AAMDNodes AATags;
   MI->getAAMetadata(AATags);
 
if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(Call)) {
     case Intrinsic::memcpy:
     case Intrinsic::memcpy_inline:
     case Intrinsic::memmove:
       assert((ArgIdx == 0 || ArgIdx == 1) &&
              "Invalid argument index for memory intrinsic");
       if (ConstantInt *LenCI = dyn_cast<ConstantInt>(II->getArgOperand(2)))
         return MemoryLocation(Arg, LocationSize::precise(LenCI->getZExtValue()),
                               AATags);
-      break;
+      return MemoryLocation::getAfter(Arg, AATags);
 
     case Intrinsic::lifetime_start:
     case Intrinsic::lifetime_end:
     case Intrinsic::invariant_start:
       assert(ArgIdx == 1 && "Invalid argument index");
       return MemoryLocation(
           Arg,
           LocationSize::precise(
case LibFunc_memset_pattern16:
       assert((ArgIdx == 0 || ArgIdx == 1) &&
              "Invalid argument index for memset_pattern16");
       if (ArgIdx == 1)
         return MemoryLocation(Arg, LocationSize::precise(16), AATags);
       if (const ConstantInt *LenCI =
               dyn_cast<ConstantInt>(Call->getArgOperand(2)))
         return MemoryLocation(Arg, LocationSize::precise(LenCI->getZExtValue()),
                               AATags);
-      break;
+      return MemoryLocation::getAfter(Arg, AATags);
     case LibFunc_bcmp:
     case LibFunc_memcmp:
       assert((ArgIdx == 0 || ArgIdx == 1) &&
              "Invalid argument index for memcmp/bcmp");
       if (const ConstantInt *LenCI =
               dyn_cast<ConstantInt>(Call->getArgOperand(2)))
         return MemoryLocation(Arg, LocationSize::precise(LenCI->getZExtValue()),
                               AATags);
-      break;
+      return MemoryLocation::getAfter(Arg, AATags);
     case LibFunc_memchr:
       assert((ArgIdx == 0) && "Invalid argument index for memchr");
       if (const ConstantInt *LenCI =
               dyn_cast<ConstantInt>(Call->getArgOperand(2)))
         return MemoryLocation(Arg, LocationSize::precise(LenCI->getZExtValue()),
                               AATags);
-      break;
+      return MemoryLocation::getAfter(Arg, AATags);
     case LibFunc_memccpy:
       assert((ArgIdx == 0 || ArgIdx == 1) &&
              "Invalid argument index for memccpy");
       // We only know an upper bound on the number of bytes read/written.
       if (const ConstantInt *LenCI =
               dyn_cast<ConstantInt>(Call->getArgOperand(3)))
         return MemoryLocation(
             Arg, LocationSize::upperBound(LenCI->getZExtValue()), AATags);
-      break;
+      return MemoryLocation::getAfter(Arg, AATags);
     default:
       break;
     };
   }
   // FIXME: Handle memset_pattern4 and memset_pattern8 also.
 
-  return MemoryLocation(Call->getArgOperand(ArgIdx), LocationSize::unknown(),
-                        AATags);
+  return MemoryLocation::getBeforeOrAfter(Call->getArgOperand(ArgIdx), AATags);
 }

llvm/lib/Analysis/MemorySSA.cpp

 } // end anonymous namespace
 
 static bool lifetimeEndsAt(MemoryDef *MD, const MemoryLocation &Loc,
                            BatchAAResults &AA) {
   Instruction *Inst = MD->getMemoryInst();
   if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) {
     switch (II->getIntrinsicID()) {
     case Intrinsic::lifetime_end: {
-      MemoryLocation ArgLoc(II->getArgOperand(1), LocationSize::unknown());
+      MemoryLocation ArgLoc = MemoryLocation::getAfter(II->getArgOperand(1));
       return AA.alias(ArgLoc, Loc) == MustAlias;
     }
     default:
       return false;
     }
   }
   return false;
 }

llvm/lib/Analysis/ObjCARCAliasAnalysis.cpp

AliasResult ObjCARCAAResult::alias(const MemoryLocation &LocA,
   if (Result != MayAlias)
     return Result;
 
   // If that failed, climb to the underlying object, including climbing through
   // ObjC-specific no-ops, and try making an imprecise alias query.
   const Value *UA = GetUnderlyingObjCPtr(SA);
   const Value *UB = GetUnderlyingObjCPtr(SB);
   if (UA != SA || UB != SB) {
-    Result = AAResultBase::alias(
-        MemoryLocation(UA, LocationSize::unknown()),
-        MemoryLocation(UB, LocationSize::unknown()), AAQI);
+    Result = AAResultBase::alias(MemoryLocation::getBeforeOrAfter(UA),
+                                 MemoryLocation::getBeforeOrAfter(UB), AAQI);
     // We can't use MustAlias or PartialAlias results here because
     // GetUnderlyingObjCPtr may return an offsetted pointer value.
     if (Result == NoAlias)
       return NoAlias;
   }
 
   // If that failed, fail. We don't need to chain here, since that's covered
   // by the earlier precise query.
if (AAResultBase::pointsToConstantMemory(
           MemoryLocation(S, Loc.Size, Loc.AATags), AAQI, OrLocal))
     return true;
 
   // If that failed, climb to the underlying object, including climbing through
   // ObjC-specific no-ops, and try making an imprecise alias query.
   const Value *U = GetUnderlyingObjCPtr(S);
   if (U != S)
     return AAResultBase::pointsToConstantMemory(
-        MemoryLocation(U, LocationSize::unknown()), AAQI, OrLocal);
+        MemoryLocation::getBeforeOrAfter(U), AAQI, OrLocal);
 
   // If that failed, fail. We don't need to chain here, since that's covered
   // by the earlier precise query.
   return false;
 }
 
 FunctionModRefBehavior ObjCARCAAResult::getModRefBehavior(const Function *F) {
   if (!EnableARCOpts)

llvm/lib/Analysis/ScalarEvolutionAliasAnalysis.cpp

AliasResult SCEVAAResult::alias(const MemoryLocation &LocA,
 
   // If ScalarEvolution can find an underlying object, form a new query.
   // The correctness of this depends on ScalarEvolution not recognizing
   // inttoptr and ptrtoint operators.
   Value *AO = GetBaseValue(AS);
   Value *BO = GetBaseValue(BS);
   if ((AO && AO != LocA.Ptr) || (BO && BO != LocB.Ptr))
     if (alias(MemoryLocation(AO ? AO : LocA.Ptr,
-                             AO ? LocationSize::unknown() : LocA.Size,
+                             AO ? LocationSize::beforeOrAfterPointer()
+                                : LocA.Size,
                              AO ? AAMDNodes() : LocA.AATags),
               MemoryLocation(BO ? BO : LocB.Ptr,
-                             BO ? LocationSize::unknown() : LocB.Size,
+                             BO ? LocationSize::beforeOrAfterPointer()
+                                : LocB.Size,
                              BO ? AAMDNodes() : LocB.AATags),
               AAQI) == NoAlias)
       return NoAlias;
 
   // Forward the query to the next analysis.
   return AAResultBase::alias(LocA, LocB, AAQI);
 }
 

llvm/lib/CodeGen/ImplicitNullChecks.cpp

for (MachineMemOperand *MMO1 : MI.memoperands()) {
     // as implicit null check.
     assert(MMO1->getValue() && "MMO1 should have a Value!");
     for (MachineMemOperand *MMO2 : PrevMI->memoperands()) {
       if (const PseudoSourceValue *PSV = MMO2->getPseudoValue()) {
         if (PSV->mayAlias(MFI))
           return AR_MayAlias;
         continue;
       }
-      llvm::AliasResult AAResult =
-          AA->alias(MemoryLocation(MMO1->getValue(), LocationSize::unknown(),
-                                   MMO1->getAAInfo()),
-                    MemoryLocation(MMO2->getValue(), LocationSize::unknown(),
-                                   MMO2->getAAInfo()));
+      llvm::AliasResult AAResult = AA->alias(
+          MemoryLocation::getAfter(MMO1->getValue(), MMO1->getAAInfo()),
+          MemoryLocation::getAfter(MMO2->getValue(), MMO2->getAAInfo()));
       if (AAResult != NoAlias)
         return AR_MayAlias;
     }
   }
   return AR_NoAlias;
 }
 
 ImplicitNullChecks::SuitabilityResult

llvm/lib/CodeGen/MachinePipeliner.cpp

else if (MI.mayLoad()) {
           if (MMO1->getValue() == MMO2->getValue() &&
               MMO1->getOffset() <= MMO2->getOffset()) {
             SDep Dep(Load, SDep::Barrier);
             Dep.setLatency(1);
             SU.addPred(Dep);
             continue;
           }
           AliasResult AAResult = AA->alias(
-              MemoryLocation(MMO1->getValue(), LocationSize::unknown(),
-                             MMO1->getAAInfo()),
-              MemoryLocation(MMO2->getValue(), LocationSize::unknown(),
-                             MMO2->getAAInfo()));
+              MemoryLocation::getAfter(MMO1->getValue(), MMO1->getAAInfo()),
+              MemoryLocation::getAfter(MMO2->getValue(), MMO2->getAAInfo()));
 
           if (AAResult != NoAlias) {
             SDep Dep(Load, SDep::Barrier);
             Dep.setLatency(1);
             SU.addPred(Dep);
           }
         }
       }

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

void SelectionDAGBuilder::visitMaskedLoad(const CallInst &I, bool IsExpanding) {
 
   AAMDNodes AAInfo;
   I.getAAMetadata(AAInfo);
   const MDNode *Ranges = I.getMetadata(LLVMContext::MD_range);
 
   // Do not serialize masked loads of constant memory with anything.
   MemoryLocation ML;
   if (VT.isScalableVector())
-    ML = MemoryLocation(PtrOperand, LocationSize::unknown());
+    ML = MemoryLocation::getAfter(PtrOperand);
   else
     ML = MemoryLocation(PtrOperand, LocationSize::precise(
                            DAG.getDataLayout().getTypeStoreSize(I.getType())),
                            AAInfo);
   bool AddToChain = !AA || !AA->pointsToConstantMemory(ML);
 
   SDValue InChain = AddToChain ? DAG.getRoot() : DAG.getEntryNode();
 

llvm/lib/Target/AMDGPU/AMDGPUAnnotateUniformValues.cpp

if (L) {
     Start = L->getHeader();
   }
 
   DFS(Start, Checklist);
   for (auto &BB : Checklist) {
     BasicBlock::iterator StartIt = (!L && (BB == Load->getParent())) ?
       BasicBlock::iterator(Load) : BB->end();
     auto Q = MDR->getPointerDependencyFrom(
-        MemoryLocation(Ptr, LocationSize::unknown()), true, StartIt, BB, Load);
+        MemoryLocation::getBeforeOrAfter(Ptr), true, StartIt, BB, Load);
     if (Q.isClobber() || Q.isUnknown())
       return true;
   }
   return false;
 }
 
 void AMDGPUAnnotateUniformValues::visitBranchInst(BranchInst &I) {
   if (DA->isUniform(&I))

llvm/lib/Target/AMDGPU/AMDGPURewriteOutArguments.cpp

for (Argument *OutArg : OutArgs) {
         continue;
 
       // An argument is convertible only if all exit blocks are able to replace
       // it.
       for (ReturnInst *RI : Returns) {
         BasicBlock *BB = RI->getParent();
 
         MemDepResult Q = MDA->getPointerDependencyFrom(
-            MemoryLocation(OutArg, LocationSize::unknown()), true, BB->end(),
-            BB, RI);
+            MemoryLocation::getBeforeOrAfter(OutArg), true, BB->end(), BB, RI);
         StoreInst *SI = nullptr;
         if (Q.isDef())
           SI = dyn_cast<StoreInst>(Q.getInst());
 
         if (SI) {
           LLVM_DEBUG(dbgs() << "Found out argument store: " << *SI << '\n');
           ReplaceableStores.emplace_back(RI, SI);
         } else {

llvm/lib/Target/ARM/ARMParallelDSP.cpp

bool ARMParallelDSP::RecordMemoryOps(BasicBlock *BB) {
   if (Loads.empty() || Loads.size() > NumLoadLimit)
     return false;
 
   using InstSet = std::set<Instruction*>;
   using DepMap = std::map<Instruction*, InstSet>;
   DepMap RAWDeps;
 
   // Record any writes that may alias a load.
-  const auto Size = LocationSize::unknown();
+  const auto Size = LocationSize::beforeOrAfterPointer();
   for (auto Write : Writes) {
     for (auto Read : Loads) {
       MemoryLocation ReadLoc =
         MemoryLocation(Read->getPointerOperand(), Size);
 
       if (!isModOrRefSet(intersectModRef(AA->getModRefInfo(Write, ReadLoc),
           ModRefInfo::ModRef)))
         continue;

llvm/lib/Target/Hexagon/HexagonLoopIdiomRecognition.cpp

 static bool
 mayLoopAccessLocation(Value *Ptr, ModRefInfo Access, Loop *L,
                       const SCEV *BECount, unsigned StoreSize,
                       AliasAnalysis &AA,
                       SmallPtrSetImpl<Instruction *> &Ignored) {
   // Get the location that may be stored across the loop.  Since the access
   // is strided positively through memory, we say that the modified location
   // starts at the pointer and has infinite size.
-  LocationSize AccessSize = LocationSize::unknown();
+  LocationSize AccessSize = LocationSize::afterPointer();
 
   // If the loop iterates a fixed number of times, we can refine the access
   // size to be exactly the size of the memset, which is (BECount+1)*StoreSize
   if (const SCEVConstant *BECst = dyn_cast<SCEVConstant>(BECount))
     AccessSize = LocationSize::precise((BECst->getValue()->getZExtValue() + 1) *
                                        StoreSize);
 
   // TODO: For this to be really effective, we have to dive into the pointer

llvm/lib/Transforms/IPO/FunctionAttrs.cpp

if (auto *Call = dyn_cast<CallBase>(I)) {
       // ignore calls that only access local memory.
       for (auto CI = Call->arg_begin(), CE = Call->arg_end(); CI != CE; ++CI) {
         Value *Arg = *CI;
         if (!Arg->getType()->isPtrOrPtrVectorTy())
           continue;
 
         AAMDNodes AAInfo;
         I->getAAMetadata(AAInfo);
-        MemoryLocation Loc(Arg, LocationSize::unknown(), AAInfo);
+        MemoryLocation Loc = MemoryLocation::getBeforeOrAfter(Arg, AAInfo);
 
         // Skip accesses to local or constant memory as they don't impact the
         // externally visible mod/ref behavior.
         if (AAR.pointsToConstantMemory(Loc, /*OrLocal=*/true))
           continue;
 
         if (isModSet(MRI))
           // Writes non-local memory.

llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp

if (auto *MI = dyn_cast<AnyMemIntrinsic>(Inst)) {
     return Loc;
   }
 
   if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) {
     switch (II->getIntrinsicID()) {
     default:
       return MemoryLocation(); // Unhandled intrinsic.
     case Intrinsic::init_trampoline:
-      return MemoryLocation(II->getArgOperand(0), LocationSize::unknown());
+      return MemoryLocation::getAfter(II->getArgOperand(0));
     case Intrinsic::masked_store:
       return MemoryLocation::getForArgument(II, 1, TLI);
     case Intrinsic::lifetime_end: {
       uint64_t Len = cast<ConstantInt>(II->getArgOperand(0))->getZExtValue();
       return MemoryLocation(II->getArgOperand(1), Len);
     }
     }
   }
   if (auto *CB = dyn_cast<CallBase>(Inst))
     // All the supported TLI functions so far happen to have dest as their
     // first argument.
-    return MemoryLocation(CB->getArgOperand(0), LocationSize::unknown());
+    return MemoryLocation::getAfter(CB->getArgOperand(0));
   return MemoryLocation();
 }
 
 /// Return the location read by the specified "hasAnalyzableMemoryWrite"
 /// instruction if any.
 static MemoryLocation getLocForRead(Instruction *Inst,
                                     const TargetLibraryInfo &TLI) {
   assert(hasAnalyzableMemoryWrite(Inst, TLI) && "Unknown instruction case");

 /// to a field of that structure.
 static bool handleFree(CallInst *F, AliasAnalysis *AA,
                        MemoryDependenceResults *MD, DominatorTree *DT,
                        const TargetLibraryInfo *TLI,
                        InstOverlapIntervalsTy &IOL,
                        MapVector<Instruction *, bool> &ThrowableInst) {
   bool MadeChange = false;
 
-  MemoryLocation Loc = MemoryLocation(F->getOperand(0),
-                                      LocationSize::unknown());
+  MemoryLocation Loc = MemoryLocation::getAfter(F->getOperand(0));
   SmallVector<BasicBlock *, 16> Blocks;
   Blocks.push_back(F->getParent());
 
   while (!Blocks.empty()) {
     BasicBlock *BB = Blocks.pop_back_val();
     Instruction *InstPt = BB->getTerminator();
     if (BB == F->getParent()) InstPt = F;
 
if (auto *CB = dyn_cast<CallBase>(I)) {
 
       LibFunc LF;
       if (TLI.getLibFunc(*CB, LF) && TLI.has(LF)) {
         switch (LF) {
         case LibFunc_strcpy:
         case LibFunc_strncpy:
         case LibFunc_strcat:
         case LibFunc_strncat:
-          return {MemoryLocation(CB->getArgOperand(0),
-                                 LocationSize::unknown())};
+          return {MemoryLocation::getAfter(CB->getArgOperand(0))};
         default:
           break;
         }
       }
       switch (CB->getIntrinsicID()) {
       case Intrinsic::init_trampoline:
-        return {MemoryLocation(CB->getArgOperand(0), LocationSize::unknown())};
+        return {MemoryLocation::getAfter(CB->getArgOperand(0))};
       case Intrinsic::masked_store:
         return {MemoryLocation::getForArgument(CB, 1, TLI)};
       default:
         break;
       }
       return None;
     }
 
getLocForTerminator(Instruction *I) const {
     uint64_t Len;
     Value *Ptr;
     if (match(I, m_Intrinsic<Intrinsic::lifetime_end>(m_ConstantInt(Len),
                                                       m_Value(Ptr))))
       return {std::make_pair(MemoryLocation(Ptr, Len), false)};
 
     if (auto *CB = dyn_cast<CallBase>(I)) {
       if (isFreeCall(I, &TLI))
-        return {std::make_pair(MemoryLocation(CB->getArgOperand(0),
-                                              LocationSize::unknown()),
+        return {std::make_pair(MemoryLocation::getAfter(CB->getArgOperand(0)),
                                true)};
     }
 
     return None;
   }
 
   /// Returns true if \p I is a memory terminator instruction like
   /// llvm.lifetime.end or free.

llvm/lib/Transforms/Scalar/LICM.cpp

if (AAResults::onlyReadsMemory(Behavior)) {
       // writes to this memory in the loop, we can hoist or sink.
       if (AAResults::onlyAccessesArgPointees(Behavior)) {
         // TODO: expand to writeable arguments
         for (Value *Op : CI->arg_operands())
           if (Op->getType()->isPointerTy()) {
             bool Invalidated;
             if (CurAST)
               Invalidated = pointerInvalidatedByLoop(
-                  MemoryLocation(Op, LocationSize::unknown(), AAMDNodes()),
-                  CurAST, CurLoop, AA);
+                  MemoryLocation::getBeforeOrAfter(Op), CurAST, CurLoop, AA);
             else
               Invalidated = pointerInvalidatedByLoopWithMSSA(
                   MSSA, cast<MemoryUse>(MSSA->getMemoryAccess(CI)), CurLoop, I,
                   *Flags);
             if (Invalidated)
               return false;
           }
         return true;

llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp

 static bool
 mayLoopAccessLocation(Value *Ptr, ModRefInfo Access, Loop *L,
                       const SCEV *BECount, unsigned StoreSize,
                       AliasAnalysis &AA,
                       SmallPtrSetImpl<Instruction *> &IgnoredStores) {
   // Get the location that may be stored across the loop.  Since the access is
   // strided positively through memory, we say that the modified location starts
   // at the pointer and has infinite size.
-  LocationSize AccessSize = LocationSize::unknown();
+  LocationSize AccessSize = LocationSize::afterPointer();
 
   // If the loop iterates a fixed number of times, we can refine the access size
   // to be exactly the size of the memset, which is (BECount+1)*StoreSize
   if (const SCEVConstant *BECst = dyn_cast<SCEVConstant>(BECount))
     AccessSize = LocationSize::precise((BECst->getValue()->getZExtValue() + 1) *
                                        StoreSize);
 
   // TODO: For this to be really effective, we have to dive into the pointer

llvm/test/Analysis/AliasSet/argmemonly.ll

 ; RUN: opt -basic-aa -print-alias-sets -S -o - < %s 2>&1 | FileCheck %s
 
 @s = global i8 1, align 1
 @d = global i8 2, align 1
 
 ; CHECK: Alias sets for function 'test_alloca_argmemonly':
 ; CHECK-NEXT: Alias Set Tracker: 2 alias sets for 3 pointer values.
 ; CHECK-NEXT: AliasSet[0x{{[0-9a-f]+}}, 1] must alias, Mod       Pointers: (i8* %a, LocationSize::precise(1))
-; CHECK-NEXT: AliasSet[0x{{[0-9a-f]+}}, 2] may alias, Mod/Ref    Pointers: (i8* %d, unknown), (i8* %s, unknown)   
+; CHECK-NEXT: AliasSet[0x{{[0-9a-f]+}}, 2] may alias, Mod/Ref    Pointers: (i8* %d, unknown before-or-after), (i8* %s, unknown before-or-after)
 define void @test_alloca_argmemonly(i8* %s, i8* %d) {
 entry:
   %a = alloca i8, align 1
   store i8 1, i8* %a, align 1
   call void @my_memcpy(i8* %d, i8* %s, i64 1)
   ret void
 }
 
 ; CHECK: Alias sets for function 'test_readonly_arg'
 ; CHECK-NEXT: Alias Set Tracker: 2 alias sets for 2 pointer values.
-; CHECK-NEXT: AliasSet[0x{{[0-9a-f]+}}, 1] must alias, Mod       Pointers: (i8* %d, unknown)
-; CHECK-NEXT: AliasSet[0x{{[0-9a-f]+}}, 1] must alias, Ref       Pointers: (i8* %s, unknown)
+; CHECK-NEXT: AliasSet[0x{{[0-9a-f]+}}, 1] must alias, Mod       Pointers: (i8* %d, unknown before-or-after)
+; CHECK-NEXT: AliasSet[0x{{[0-9a-f]+}}, 1] must alias, Ref       Pointers: (i8* %s, unknown before-or-after)
 define i8 @test_readonly_arg(i8* noalias %s, i8* noalias %d) {
 entry:
   call void @my_memcpy(i8* %d, i8* %s, i64 1)
   %ret = load i8, i8* %s
   ret i8 %ret
 }
 
 ; CHECK: Alias sets for function 'test_noalias_argmemonly':
 ; CHECK-NEXT: Alias Set Tracker: 2 alias sets for 3 pointer values.
 ; CHECK-NEXT: AliasSet[0x{{[0-9a-f]+}}, 1] must alias, Mod       Pointers: (i8* %a, LocationSize::precise(1))
-; CHECK-NEXT: AliasSet[0x{{[0-9a-f]+}}, 2] may alias, Mod/Ref    Pointers: (i8* %d, unknown), (i8* %s, unknown)   
+; CHECK-NEXT: AliasSet[0x{{[0-9a-f]+}}, 2] may alias, Mod/Ref    Pointers: (i8* %d, unknown before-or-after), (i8* %s, unknown before-or-after)
 define void @test_noalias_argmemonly(i8* noalias %a, i8* %s, i8* %d) {
 entry:
   store i8 1, i8* %a, align 1
   call void @my_memmove(i8* %d, i8* %s, i64 1)
   ret void
 }
 
 ; CHECK: Alias sets for function 'test5':
 ; CHECK-NEXT: Alias Set Tracker: 2 alias sets for 2 pointer values.
-; CHECK-NEXT: AliasSet[0x{{[0-9a-f]+}}, 1] must alias, Mod/Ref Pointers: (i8* %a, unknown)
-; CHECK-NEXT: AliasSet[0x{{[0-9a-f]+}}, 1] must alias, Mod Pointers: (i8* %b, unknown)
+; CHECK-NEXT: AliasSet[0x{{[0-9a-f]+}}, 1] must alias, Mod/Ref Pointers: (i8* %a, unknown before-or-after)
+; CHECK-NEXT: AliasSet[0x{{[0-9a-f]+}}, 1] must alias, Mod Pointers: (i8* %b, unknown before-or-after)
 define void @test5(i8* noalias %a, i8* noalias %b) {
 entry:
   store i8 1, i8* %a, align 1
   call void @my_memcpy(i8* %b, i8* %a, i64 1)
   store i8 1, i8* %b, align 1
   ret void
 }
 
 ; CHECK: Alias sets for function 'test_argcollapse':
 ; CHECK-NEXT: Alias Set Tracker: 2 alias sets for 2 pointer values.
-; CHECK-NEXT: AliasSet[0x{{[0-9a-f]+}}, 1] must alias, Mod/Ref Pointers: (i8* %a, unknown)
-; CHECK-NEXT: AliasSet[0x{{[0-9a-f]+}}, 1] must alias, Mod/Ref Pointers: (i8* %b, unknown)
+; CHECK-NEXT: AliasSet[0x{{[0-9a-f]+}}, 1] must alias, Mod/Ref Pointers: (i8* %a, unknown before-or-after)
+; CHECK-NEXT: AliasSet[0x{{[0-9a-f]+}}, 1] must alias, Mod/Ref Pointers: (i8* %b, unknown before-or-after)
 define void @test_argcollapse(i8* noalias %a, i8* noalias %b) {
 entry:
   store i8 1, i8* %a, align 1
   call void @my_memmove(i8* %b, i8* %a, i64 1)
   store i8 1, i8* %b, align 1
   ret void
 }
 
 ; CHECK: Alias sets for function 'test_memcpy1':
 ; CHECK-NEXT: Alias Set Tracker: 2 alias sets for 2 pointer values.
-; CHECK-NEXT: AliasSet[0x{{[0-9a-f]+}}, 1] must alias, Mod/Ref Pointers: (i8* %b, unknown)
-; CHECK-NEXT: AliasSet[0x{{[0-9a-f]+}}, 1] must alias, Mod/Ref Pointers: (i8* %a, unknown)
+; CHECK-NEXT: AliasSet[0x{{[0-9a-f]+}}, 1] must alias, Mod/Ref Pointers: (i8* %b, unknown before-or-after)
+; CHECK-NEXT: AliasSet[0x{{[0-9a-f]+}}, 1] must alias, Mod/Ref Pointers: (i8* %a, unknown before-or-after)
 define void @test_memcpy1(i8* noalias %a, i8* noalias %b) {
 entry:
   call void @my_memcpy(i8* %b, i8* %a, i64 1)
   call void @my_memcpy(i8* %a, i8* %b, i64 1)
   ret void
 }
 
 ; CHECK: Alias sets for function 'test_memset1':
 ; CHECK-NEXT: Alias Set Tracker: 1 alias sets for 1 pointer values.
-; CHECK-NEXT: AliasSet[0x{{[0-9a-f]+}}, 1] must alias, Mod Pointers: (i8* %a, unknown)
+; CHECK-NEXT: AliasSet[0x{{[0-9a-f]+}}, 1] must alias, Mod Pointers: (i8* %a, unknown before-or-after)
 define void @test_memset1() {
 entry:
   %a = alloca i8, align 1
   call void @my_memset(i8* %a, i8 0, i64 1)
   ret void
 }
 
 ; CHECK: Alias sets for function 'test_memset2':
 ; CHECK-NEXT: Alias Set Tracker: 1 alias sets for 1 pointer values.
-; CHECK-NEXT: AliasSet[0x{{[0-9a-f]+}}, 1] must alias, Mod Pointers: (i8* %a, unknown)
+; CHECK-NEXT: AliasSet[0x{{[0-9a-f]+}}, 1] must alias, Mod Pointers: (i8* %a, unknown before-or-after)
 define void @test_memset2(i8* %a) {
 entry:
   call void @my_memset(i8* %a, i8 0, i64 1)
   ret void
 }
 
 ; CHECK: Alias sets for function 'test_memset3':
 ; CHECK-NEXT: Alias Set Tracker: 1 alias sets for 2 pointer values.
-; CHECK-NEXT: AliasSet[0x{{[0-9a-f]+}}, 2] may alias, Mod Pointers: (i8* %a, unknown), (i8* %b, unknown)
+; CHECK-NEXT: AliasSet[0x{{[0-9a-f]+}}, 2] may alias, Mod Pointers: (i8* %a, unknown before-or-after), (i8* %b, unknown before-or-after)
 define void @test_memset3(i8* %a, i8* %b) {
 entry:
   call void @my_memset(i8* %a, i8 0, i64 1)
   call void @my_memset(i8* %b, i8 0, i64 1)
   ret void
 }
 
 ;; PICKUP HERE
 
 ; CHECK: Alias sets for function 'test_memset4':
 ; CHECK-NEXT: Alias Set Tracker: 2 alias sets for 2 pointer values.
-; CHECK-NEXT: AliasSet[0x{{[0-9a-f]+}}, 1] must alias, Mod Pointers: (i8* %a, unknown)
-; CHECK-NEXT: AliasSet[0x{{[0-9a-f]+}}, 1] must alias, Mod Pointers: (i8* %b, unknown)
+; CHECK-NEXT: AliasSet[0x{{[0-9a-f]+}}, 1] must alias, Mod Pointers: (i8* %a, unknown before-or-after)
+; CHECK-NEXT: AliasSet[0x{{[0-9a-f]+}}, 1] must alias, Mod Pointers: (i8* %b, unknown before-or-after)
 define void @test_memset4(i8* noalias %a, i8* noalias %b) {
 entry:
   call void @my_memset(i8* %a, i8 0, i64 1)
   call void @my_memset(i8* %b, i8 0, i64 1)
   ret void
 }
 
 declare void @my_memset(i8* nocapture writeonly, i8, i64) argmemonly

llvm/test/Analysis/AliasSet/memset.ll

 ; RUN: opt -basic-aa -print-alias-sets -S -o - < %s 2>&1 | FileCheck %s
 
 @s = global i8 1, align 1
 @d = global i8 2, align 1
 
 ; CHECK: Alias sets for function 'test_known_size':
 ; CHECK: Alias Set Tracker: 1 alias sets for 1 pointer values.
 ; CHECK:   AliasSet[0x{{[0-9a-f]+}}, 1] must alias, Mod       Pointers: (i8* %d, LocationSize::precise(1))
 define void @test_known_size(i8* noalias %d) {
 entry:
   call void @llvm.memset.p0i8.i64(i8* align 1 %d, i8 0, i64 1, i1 false)
   ret void
 }
 
 ; CHECK: Alias sets for function 'test_unknown_size':
 ; CHECK: Alias Set Tracker: 1 alias sets for 1 pointer values.
-; CHECK:   AliasSet[0x{{[0-9a-f]+}}, 1] must alias, Mod       Pointers: (i8* %d, unknown)
+; CHECK:   AliasSet[0x{{[0-9a-f]+}}, 1] must alias, Mod       Pointers: (i8* %d, unknown after)
 define void @test_unknown_size(i8* noalias %d, i64 %len) {
 entry:
   call void @llvm.memset.p0i8.i64(i8* align 1 %d, i8 0, i64 %len, i1 false)
   ret void
 }
 
 
 ; CHECK: Alias sets for function 'test_atomic_known_size':
 ; CHECK: Alias Set Tracker: 1 alias sets for 1 pointer values.
 ; CHECK:   AliasSet[0x{{[0-9a-f]+}}, 1] must alias, Mod       Pointers: (i8* %d, LocationSize::precise(1))
 define void @test_atomic_known_size(i8* noalias %d) {
 entry:
   call void @llvm.memset.element.unordered.atomic.p0i8.i32(i8* align 1 %d, i8 0, i64 1, i32 1)
   ret void
 }
 
 ; CHECK: Alias sets for function 'test_atomic_unknown_size':
 ; CHECK: Alias Set Tracker: 1 alias sets for 1 pointer values.
-; CHECK:   AliasSet[0x{{[0-9a-f]+}}, 1] must alias, Mod       Pointers: (i8* %d, unknown)
+; CHECK:   AliasSet[0x{{[0-9a-f]+}}, 1] must alias, Mod       Pointers: (i8* %d, unknown after)
 define void @test_atomic_unknown_size(i8* noalias %d, i64 %len) {
 entry:
   call void @llvm.memset.element.unordered.atomic.p0i8.i32(i8* align 1 %d, i8 0, i64 %len, i32 1)
   ret void
 }
 
 declare void @llvm.memset.p0i8.i64(i8* %dest, i8 %val,
                                    i64 %len, i1 %isvolatile)
 declare void @llvm.memset.element.unordered.atomic.p0i8.i32(i8* %dest,
                                                             i8 %value,
                                                             i64 %len,
                                                             i32 %element_size)

llvm/test/Analysis/AliasSet/memtransfer.ll

 define void @test_known_size(i8* noalias %s, i8* noalias %d) {
 entry:
   call void @llvm.memcpy.p0i8.p0i8.i64(i8* %d, i8* %s, i64 1, i1 false)
   ret void
 }
 
 ; CHECK: Alias sets for function 'test_unknown_size':
 ; CHECK: Alias Set Tracker: 2 alias sets for 2 pointer values.
-; CHECK:   AliasSet[0x{{[0-9a-f]+}}, 1] must alias, Mod       Pointers: (i8* %d, unknown)
-; CHECK:   AliasSet[0x{{[0-9a-f]+}}, 1] must alias, Ref       Pointers: (i8* %s, unknown)
+; CHECK:   AliasSet[0x{{[0-9a-f]+}}, 1] must alias, Mod       Pointers: (i8* %d, unknown after)
+; CHECK:   AliasSet[0x{{[0-9a-f]+}}, 1] must alias, Ref       Pointers: (i8* %s, unknown after)
 define void @test_unknown_size(i8* noalias %s, i8* noalias %d, i64 %len) {
 entry:
   call void @llvm.memcpy.p0i8.p0i8.i64(i8* %d, i8* %s, i64 %len, i1 false)
   ret void
 }
 
 
 ; CHECK: Alias sets for function 'test1':

llvm/test/Analysis/BasicAA/cs-cs.ll

entry:
   call void @an_inaccessiblememonly_func()
   call void @an_inaccessibleorargmemonly_func(i8* %q)
   call void @an_argmemonly_func(i8* %q)
   ret void
 
 ; CHECK-LABEL: Function: test8
 ; CHECK: NoModRef:  Ptr: i8* %p <->  call void @an_inaccessiblememonly_func()
 ; CHECK: NoModRef:  Ptr: i8* %q <->  call void @an_inaccessiblememonly_func()
-; CHECK: NoModRef:  Ptr: i8* %p <->  call void @an_inaccessibleorargmemonly_func(i8* %q)
+; CHECK: Both ModRef:  Ptr: i8* %p <->  call void @an_inaccessibleorargmemonly_func(i8* %q)
 ; CHECK: Both ModRef (MustAlias):  Ptr: i8* %q <->  call void @an_inaccessibleorargmemonly_func(i8* %q)
-; CHECK: NoModRef:  Ptr: i8* %p <->  call void @an_argmemonly_func(i8* %q)
+; CHECK: Both ModRef:  Ptr: i8* %p <->  call void @an_argmemonly_func(i8* %q)
 ; CHECK: Both ModRef (MustAlias):  Ptr: i8* %q <->  call void @an_argmemonly_func(i8* %q)
 ; CHECK: Just Ref: call void @a_readonly_func(i8* %p) <-> call void @an_inaccessiblememonly_func()
 ; CHECK: Just Ref: call void @a_readonly_func(i8* %p) <-> call void @an_inaccessibleorargmemonly_func(i8* %q)
 ; CHECK: Just Ref: call void @a_readonly_func(i8* %p) <-> call void @an_argmemonly_func(i8* %q)
 ; CHECK: Both ModRef: call void @an_inaccessiblememonly_func() <-> call void @a_readonly_func(i8* %p)
 ; CHECK: Both ModRef: call void @an_inaccessiblememonly_func() <-> call void @a_writeonly_func(i8* %q)
 ; CHECK: Both ModRef: call void @an_inaccessiblememonly_func() <-> call void @an_inaccessiblememonly_func()
 ; CHECK: Both ModRef: call void @an_inaccessiblememonly_func() <-> call void @an_inaccessibleorargmemonly_func(i8* %q)
entry:
   call void @an_inaccessibleorargmemonly_func(i8* %q) #8 [ "unknown"() ]
   call void @an_argmemonly_func(i8* %q) #9 [ "unknown"() ]
   ret void
 
 ; CHECK: Just Ref:  Ptr: i8* %p        <->  call void @a_readonly_func(i8* %p) #9 [ "unknown"() ]
 ; CHECK: Just Ref:  Ptr: i8* %q        <->  call void @a_readonly_func(i8* %p) #9 [ "unknown"() ]
 ; CHECK: NoModRef:  Ptr: i8* %p        <->  call void @an_inaccessiblememonly_func() #10 [ "unknown"() ]
 ; CHECK: NoModRef:  Ptr: i8* %q        <->  call void @an_inaccessiblememonly_func() #10 [ "unknown"() ]
-; CHECK: NoModRef:  Ptr: i8* %p        <->  call void @an_inaccessibleorargmemonly_func(i8* %q) #11 [ "unknown"() ]
+; CHECK: Both ModRef:  Ptr: i8* %p        <->  call void @an_inaccessibleorargmemonly_func(i8* %q) #11 [ "unknown"() ]
 ; CHECK: Both ModRef (MustAlias):  Ptr: i8* %q     <->  call void @an_inaccessibleorargmemonly_func(i8* %q) #11 [ "unknown"() ]
-; CHECK: NoModRef:  Ptr: i8* %p        <->  call void @an_argmemonly_func(i8* %q) #12 [ "unknown"() ]
+; CHECK: Both ModRef:  Ptr: i8* %p        <->  call void @an_argmemonly_func(i8* %q) #12 [ "unknown"() ]
 ; CHECK: Both ModRef (MustAlias):  Ptr: i8* %q     <->  call void @an_argmemonly_func(i8* %q) #12 [ "unknown"() ]
 ; CHECK: Just Ref:   call void @a_readonly_func(i8* %p) #9 [ "unknown"() ] <->   call void @an_inaccessiblememonly_func() #10 [ "unknown"() ]
 ; CHECK: Just Ref:   call void @a_readonly_func(i8* %p) #9 [ "unknown"() ] <->   call void @an_inaccessibleorargmemonly_func(i8* %q) #11 [ "unknown"() ]
 ; CHECK: Just Ref:   call void @a_readonly_func(i8* %p) #9 [ "unknown"() ] <->   call void @an_argmemonly_func(i8* %q) #12 [ "unknown"() ]
 ; CHECK: Both ModRef:   call void @an_inaccessiblememonly_func() #10 [ "unknown"() ] <->   call void @a_readonly_func(i8* %p) #9 [ "unknown"() ]
 ; CHECK: Both ModRef:   call void @an_inaccessiblememonly_func() #10 [ "unknown"() ] <->   call void @an_inaccessibleorargmemonly_func(i8* %q) #11 [ "unknown"() ]
 ; CHECK: NoModRef:   call void @an_inaccessiblememonly_func() #10 [ "unknown"() ] <->   call void @an_argmemonly_func(i8* %q) #12 [ "unknown"() ]
 ; CHECK: Both ModRef:   call void @an_inaccessibleorargmemonly_func(i8* %q) #11 [ "unknown"() ] <->   call void @a_readonly_func(i8* %p) #9 [ "unknown"() ]

llvm/test/CodeGen/AMDGPU/global_smrd_cfg.ll

 ; RUN: llc -mtriple amdgcn--amdhsa -mcpu=fiji -amdgpu-scalarize-global-loads=true -verify-machineinstrs  < %s | FileCheck %s
 
 ; CHECK-LABEL: %bb22
 
 ; Load from %arg has alias store in Loop
 
 ; CHECK: flat_load_dword
 
 ; #####################################################################
 
 ; Load from %arg1 has no-alias store in Loop - arg1[i+1] never alias arg1[i]
+; However, our analysis cannot detect this.
 
-; CHECK: s_load_dword
+; CHECK: flat_load_dword
 
 ; #####################################################################
 
 ; CHECK-LABEL: %bb11
 
 ; Load from %arg in a Loop body has alias store
 
 ; CHECK: flat_load_dword

llvm/unittests/Analysis/AliasAnalysisTest.cpp

for (Argument &A : F.args())
       if (A.getType()->isPointerTy())
         Pointers.insert(&A);
     for (Instruction &I : instructions(F))
       if (I.getType()->isPointerTy())
         Pointers.insert(&I);
 
     for (Value *P1 : Pointers)
       for (Value *P2 : Pointers)
-        (void)AA.alias(P1, LocationSize::unknown(), P2,
-                       LocationSize::unknown());
+        (void)AA.alias(P1, LocationSize::beforeOrAfterPointer(), P2,
+                       LocationSize::beforeOrAfterPointer());
 
     return false;
   }
 };
 }
 
 char AATestPass::ID = 0;
 INITIALIZE_PASS_BEGIN(AATestPass, "aa-test-pas", "Alias Analysis Test Pass",

llvm/unittests/Analysis/MemorySSATest.cpp

TEST_F(MemorySSATest, LifetimeMarkersAreClobbers) {
   EXPECT_EQ(BarClobber, LifetimeStartAccess);
 
   MemoryAccess *BazClobber =
       MSSA.getWalker()->getClobberingMemoryAccess(BazAccess);
   EXPECT_EQ(BazClobber, LifetimeStartAccess);
 
   MemoryAccess *LifetimeStartClobber =
       MSSA.getWalker()->getClobberingMemoryAccess(
-          LifetimeStartAccess, MemoryLocation(Foo, LocationSize::unknown()));
+          LifetimeStartAccess, MemoryLocation::getAfter(Foo));
   EXPECT_EQ(LifetimeStartClobber, LifetimeStartAccess);
 }
 
 TEST_F(MemorySSATest, DefOptimizationsAreInvalidatedOnMoving) {
   IRBuilder<> B(C);
   F = Function::Create(FunctionType::get(B.getVoidTy(), {B.getInt1Ty()}, false),
                        GlobalValue::ExternalLinkage, "F", &M);
 

polly/lib/Analysis/ScopDetection.cpp

bool ScopDetection::isValidAccess(Instruction *Inst, const SCEV *AF,
   if (IgnoreAliasing)
     return true;
 
   // Check if the base pointer of the memory access does alias with
   // any other pointer. This cannot be handled at the moment.
   AAMDNodes AATags;
   Inst->getAAMetadata(AATags);
   AliasSet &AS = Context.AST.getAliasSetFor(
-      MemoryLocation(BP->getValue(), LocationSize::unknown(), AATags));
+      MemoryLocation::getBeforeOrAfter(BP->getValue(), AATags));
 
   if (!AS.isMustAlias()) {
     if (PollyUseRuntimeAliasChecks) {
       bool CanBuildRunTimeCheck = true;
       // The run-time alias check places code that involves the base pointer at
       // the beginning of the SCoP. This breaks if the base pointer is defined
       // inside the scop. Hence, we can only create a run-time check if we are
       // sure the base pointer is not an instruction defined inside the scop.