[ValueTracking] Add MustPreserveNullness arg to functions analyzing calls. (NFC)

Some uses of getArgumentAliasingToReturnedPointer and
isIntrinsicReturningPointerAliasingArgumentWithoutCapturing require the
calls/intrinsics to preserve the nullness of the argument.

For alias analysis, the nullness property does not really come into
play.

This patch explicitly sets it to true. In D61669, the alias analysis
uses will be switched to not require preserving nullness.

Reviewers: nlopes, efriedma, hfinkel, sanjoy, aqjune, jdoerfert

Reviewed By: jdoerfert

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D64150

llvm-svn: 368993

llvm/include/llvm/Analysis/ValueTracking.h

@@ -307,20 +307,26 @@ class Value;
   uint64_t GetStringLength(const Value *V, unsigned CharSize = 8);
 
   /// This function returns call pointer argument that is considered the same by
-  /// aliasing rules. You CAN'T use it to replace one value with another.
-  const Value *getArgumentAliasingToReturnedPointer(const CallBase *Call);
-  inline Value *getArgumentAliasingToReturnedPointer(CallBase *Call) {
+  /// aliasing rules. You CAN'T use it to replace one value with another. If
+  /// \p MustPreserveNullness is true, the call must preserve the nullness of
+  /// the pointer.
+  const Value *getArgumentAliasingToReturnedPointer(const CallBase *Call,
+                                                    bool MustPreserveNullness);
+  inline Value *
+  getArgumentAliasingToReturnedPointer(CallBase *Call,
+                                       bool MustPreserveNullness) {
     return const_cast<Value *>(getArgumentAliasingToReturnedPointer(
-        const_cast<const CallBase *>(Call)));
+        const_cast<const CallBase *>(Call), MustPreserveNullness));
   }
 
-  // {launder,strip}.invariant.group returns pointer that aliases its argument,
-  // and it only captures pointer by returning it.
-  // These intrinsics are not marked as nocapture, because returning is
-  // considered as capture. The arguments are not marked as returned neither,
-  // because it would make it useless.
+  /// {launder,strip}.invariant.group returns pointer that aliases its argument,
+  /// and it only captures pointer by returning it.
+  /// These intrinsics are not marked as nocapture, because returning is
+  /// considered as capture. The arguments are not marked as returned neither,
+  /// because it would make it useless. If \p MustPreserveNullness is true,
+  /// the intrinsic must preserve the nullness of the pointer.
   bool isIntrinsicReturningPointerAliasingArgumentWithoutCapturing(
-      const CallBase *Call);
+      const CallBase *Call, bool MustPreserveNullness);
 
   /// This method strips off any GEP address adjustments and pointer casts from
   /// the specified value, returning the original object being addressed. Note

llvm/lib/Analysis/BasicAliasAnalysis.cpp

@@ -481,7 +481,7 @@ bool BasicAAResult::DecomposeGEPExpression(const Value *V,
         // because it should be in sync with CaptureTracking. Not using it may
         // cause weird miscompilations where 2 aliasing pointers are assumed to
         // noalias.
-        if (auto *RP = getArgumentAliasingToReturnedPointer(Call)) {
+        if (auto *RP = getArgumentAliasingToReturnedPointer(Call, true)) {
           V = RP;
           continue;
         }

llvm/lib/Analysis/CaptureTracking.cpp

@@ -251,7 +251,8 @@ void llvm::PointerMayBeCaptured(const Value *V, CaptureTracker *Tracker,
       // marked with nocapture do not capture. This means that places like
       // GetUnderlyingObject in ValueTracking or DecomposeGEPExpression
       // in BasicAA also need to know about this property.
-      if (isIntrinsicReturningPointerAliasingArgumentWithoutCapturing(Call)) {
+      if (isIntrinsicReturningPointerAliasingArgumentWithoutCapturing(Call,
+                                                                      true)) {
         AddUses(Call);
         break;
       }

llvm/lib/Analysis/Loads.cpp

@@ -107,7 +107,7 @@ static bool isDereferenceableAndAlignedPointer(
                                               DL, CtxI, DT, Visited);
 
   if (const auto *Call = dyn_cast<CallBase>(V))
-    if (auto *RP = getArgumentAliasingToReturnedPointer(Call))
+    if (auto *RP = getArgumentAliasingToReturnedPointer(Call, true))
       return isDereferenceableAndAlignedPointer(RP, Align, Size, DL, CtxI, DT,
                                                 Visited);
 

llvm/lib/Analysis/ValueTracking.cpp

@@ -2073,7 +2073,7 @@ bool isKnownNonZero(const Value *V, unsigned Depth, const Query &Q) {
     if (const auto *Call = dyn_cast<CallBase>(V)) {
       if (Call->isReturnNonNull())
         return true;
-      if (const auto *RP = getArgumentAliasingToReturnedPointer(Call))
+      if (const auto *RP = getArgumentAliasingToReturnedPointer(Call, true))
         return isKnownNonZero(RP, Depth, Q);
     }
   }
@@ -3658,19 +3658,22 @@ uint64_t llvm::GetStringLength(const Value *V, unsigned CharSize) {
   return Len == ~0ULL ? 1 : Len;
 }
 
-const Value *llvm::getArgumentAliasingToReturnedPointer(const CallBase *Call) {
+const Value *
+llvm::getArgumentAliasingToReturnedPointer(const CallBase *Call,
+                                           bool MustPreserveNullness) {
   assert(Call &&
          "getArgumentAliasingToReturnedPointer only works on nonnull calls");
   if (const Value *RV = Call->getReturnedArgOperand())
     return RV;
   // This can be used only as a aliasing property.
-  if (isIntrinsicReturningPointerAliasingArgumentWithoutCapturing(Call))
+  if (isIntrinsicReturningPointerAliasingArgumentWithoutCapturing(
+          Call, MustPreserveNullness))
     return Call->getArgOperand(0);
   return nullptr;
 }
 
 bool llvm::isIntrinsicReturningPointerAliasingArgumentWithoutCapturing(
-    const CallBase *Call) {
+    const CallBase *Call, bool MustPreserveNullness) {
   return Call->getIntrinsicID() == Intrinsic::launder_invariant_group ||
          Call->getIntrinsicID() == Intrinsic::strip_invariant_group ||
          Call->getIntrinsicID() == Intrinsic::aarch64_irg ||
@@ -3732,7 +3735,7 @@ Value *llvm::GetUnderlyingObject(Value *V, const DataLayout &DL,
         // because it should be in sync with CaptureTracking. Not using it may
         // cause weird miscompilations where 2 aliasing pointers are assumed to
         // noalias.
-        if (auto *RP = getArgumentAliasingToReturnedPointer(Call)) {
+        if (auto *RP = getArgumentAliasingToReturnedPointer(Call, true)) {
           V = RP;
           continue;
         }