Add support for non-zero null pointer for C and OpenCL

In amdgcn target, null pointers in global, constant, and generic address space take value 0 but null pointers in private and local address space take value -1. Currently LLVM assumes all null pointers take value 0, which results in incorrectly translated IR. To workaround this issue, instead of emit null pointers in local and private address space, a null pointer in generic address space is emitted and casted to local and private address space.

Tentative definition of global variables with non-zero initializer will have weak linkage instead of common linkage since common linkage requires zero initializer and does not have explicit section to hold the non-zero value.

Virtual member functions getNullPointer and performAddrSpaceCast are added to TargetCodeGenInfo which by default returns ConstantPointerNull and emitting addrspacecast instruction. A virtual member function getNullPointerValue is added to TargetInfo which by default returns 0. Each target can override these virtual functions to get target specific null pointer and the null pointer value for specific address space, and perform specific translations for addrspacecast.

Wrapper functions getNullPointer is added to CodegenModule and getTargetNullPointerValue is added to ASTContext to facilitate getting the target specific null pointers and their values.

This change has no effect on other targets except amdgcn target. Other targets can provide support of non-zero null pointer in a similar way.

This change only provides support for non-zero null pointer for C and OpenCL. Supporting for other languages will be added later incrementally.

Differential Revision: https://reviews.llvm.org/D26196


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@289252 91177308-0d34-0410-b5e6-96231b3b80d8

18 files changed, 765 insertions, 67 deletions

diff --git a/include/clang/AST/APValue.h b/include/clang/AST/APValue.h
index e58c21923f..7c431f3be8 100644
--- a/include/clang/AST/APValue.h
+++ b/include/clang/AST/APValue.h
@@ -135,14 +135,15 @@ public:
   }
   APValue(const APValue &RHS);
   APValue(APValue &&RHS) : Kind(Uninitialized) { swap(RHS); }
-  APValue(LValueBase B, const CharUnits &O, NoLValuePath N, unsigned CallIndex)
+  APValue(LValueBase B, const CharUnits &O, NoLValuePath N, unsigned CallIndex,
+          bool IsNullPtr = false)
       : Kind(Uninitialized) {
-    MakeLValue(); setLValue(B, O, N, CallIndex);
+    MakeLValue(); setLValue(B, O, N, CallIndex, IsNullPtr);
   }
   APValue(LValueBase B, const CharUnits &O, ArrayRef<LValuePathEntry> Path,
-          bool OnePastTheEnd, unsigned CallIndex)
+          bool OnePastTheEnd, unsigned CallIndex, bool IsNullPtr = false)
       : Kind(Uninitialized) {
-    MakeLValue(); setLValue(B, O, Path, OnePastTheEnd, CallIndex);
+    MakeLValue(); setLValue(B, O, Path, OnePastTheEnd, CallIndex, IsNullPtr);
   }
   APValue(UninitArray, unsigned InitElts, unsigned Size) : Kind(Uninitialized) {
     MakeArray(InitElts, Size);
@@ -254,6 +255,7 @@ public:
   bool hasLValuePath() const;
   ArrayRef<LValuePathEntry> getLValuePath() const;
   unsigned getLValueCallIndex() const;
+  bool isNullPointer() const;
 
   APValue &getVectorElt(unsigned I) {
     assert(isVector() && "Invalid accessor");
@@ -374,10 +376,10 @@ public:
     ((ComplexAPFloat *)(char *)Data.buffer)->Imag = std::move(I);
   }
   void setLValue(LValueBase B, const CharUnits &O, NoLValuePath,
-                 unsigned CallIndex);
+                 unsigned CallIndex, bool IsNullPtr);
   void setLValue(LValueBase B, const CharUnits &O,
                  ArrayRef<LValuePathEntry> Path, bool OnePastTheEnd,
-                 unsigned CallIndex);
+                 unsigned CallIndex, bool IsNullPtr);
   void setUnion(const FieldDecl *Field, const APValue &Value) {
     assert(isUnion() && "Invalid accessor");
     ((UnionData*)(char*)Data.buffer)->Field = Field;
diff --git a/include/clang/AST/ASTContext.h b/include/clang/AST/ASTContext.h
index 4f35508eba..4e35ae833d 100644
--- a/include/clang/AST/ASTContext.h
+++ b/include/clang/AST/ASTContext.h
@@ -2295,6 +2295,10 @@ public:
       return (*AddrSpaceMap)[AS - LangAS::Offset];
   }
 
+  /// Get target-dependent integer value for null pointer which is used for
+  /// constant folding.
+  uint64_t getTargetNullPointerValue(QualType QT) const;
+
   bool addressSpaceMapManglingFor(unsigned AS) const {
     return AddrSpaceMapMangling || 
            AS < LangAS::Offset || 
diff --git a/include/clang/Basic/TargetInfo.h b/include/clang/Basic/TargetInfo.h
index b6b9aea690..ec566f0642 100644
--- a/include/clang/Basic/TargetInfo.h
+++ b/include/clang/Basic/TargetInfo.h
@@ -42,6 +42,7 @@ class DiagnosticsEngine;
 class LangOptions;
 class CodeGenOptions;
 class MacroBuilder;
+class QualType;
 class SourceLocation;
 class SourceManager;
 
@@ -300,6 +301,12 @@ public:
     return PointerWidth;
   }
 
+  /// \brief Get integer value for null pointer.
+  /// \param AddrSpace address space of pointee in source language.
+  virtual uint64_t getNullPointerValue(unsigned AddrSpace) const {
+    return 0;
+  }
+
   /// \brief Return the size of '_Bool' and C++ 'bool' for this target, in bits.
   unsigned getBoolWidth() const { return BoolWidth; }
 
diff --git a/lib/AST/APValue.cpp b/lib/AST/APValue.cpp
index 5e1938cb5f..8ee71e2fb2 100644
--- a/lib/AST/APValue.cpp
+++ b/lib/AST/APValue.cpp
@@ -27,6 +27,7 @@ namespace {
     CharUnits Offset;
     unsigned PathLength;
     unsigned CallIndex;
+    bool IsNullPtr;
   };
 }
 
@@ -149,10 +150,11 @@ APValue::APValue(const APValue &RHS) : Kind(Uninitialized) {
     MakeLValue();
     if (RHS.hasLValuePath())
       setLValue(RHS.getLValueBase(), RHS.getLValueOffset(), RHS.getLValuePath(),
-                RHS.isLValueOnePastTheEnd(), RHS.getLValueCallIndex());
+                RHS.isLValueOnePastTheEnd(), RHS.getLValueCallIndex(),
+                RHS.isNullPointer());
     else
       setLValue(RHS.getLValueBase(), RHS.getLValueOffset(), NoLValuePath(),
-                RHS.getLValueCallIndex());
+                RHS.getLValueCallIndex(), RHS.isNullPointer());
     break;
   case Array:
     MakeArray(RHS.getArrayInitializedElts(), RHS.getArraySize());
@@ -579,8 +581,13 @@ unsigned APValue::getLValueCallIndex() const {
   return ((const LV*)(const char*)Data.buffer)->CallIndex;
 }
 
+bool APValue::isNullPointer() const {
+  assert(isLValue() && "Invalid usage");
+  return ((const LV*)(const char*)Data.buffer)->IsNullPtr;
+}
+
 void APValue::setLValue(LValueBase B, const CharUnits &O, NoLValuePath,
-                        unsigned CallIndex) {
+                        unsigned CallIndex, bool IsNullPtr) {
   assert(isLValue() && "Invalid accessor");
   LV &LVal = *((LV*)(char*)Data.buffer);
   LVal.BaseAndIsOnePastTheEnd.setPointer(B);
@@ -588,11 +595,12 @@ void APValue::setLValue(LValueBase B, const CharUnits &O, NoLValuePath,
   LVal.Offset = O;
   LVal.CallIndex = CallIndex;
   LVal.resizePath((unsigned)-1);
+  LVal.IsNullPtr = IsNullPtr;
 }
 
 void APValue::setLValue(LValueBase B, const CharUnits &O,
                         ArrayRef<LValuePathEntry> Path, bool IsOnePastTheEnd,
-                        unsigned CallIndex) {
+                        unsigned CallIndex, bool IsNullPtr) {
   assert(isLValue() && "Invalid accessor");
   LV &LVal = *((LV*)(char*)Data.buffer);
   LVal.BaseAndIsOnePastTheEnd.setPointer(B);
@@ -601,6 +609,7 @@ void APValue::setLValue(LValueBase B, const CharUnits &O,
   LVal.CallIndex = CallIndex;
   LVal.resizePath(Path.size());
   memcpy(LVal.getPath(), Path.data(), Path.size() * sizeof(LValuePathEntry));
+  LVal.IsNullPtr = IsNullPtr;
 }
 
 const ValueDecl *APValue::getMemberPointerDecl() const {
diff --git a/lib/AST/ASTContext.cpp b/lib/AST/ASTContext.cpp
index 22be71a727..a4861d982e 100644
--- a/lib/AST/ASTContext.cpp
+++ b/lib/AST/ASTContext.cpp
@@ -9426,6 +9426,16 @@ ASTContext::ObjCMethodsAreEqual(const ObjCMethodDecl *MethodDecl,
   
 }
 
+uint64_t ASTContext::getTargetNullPointerValue(QualType QT) const {
+  unsigned AS;
+  if (QT->getUnqualifiedDesugaredType()->isNullPtrType())
+    AS = 0;
+  else
+    AS = QT->getPointeeType().getAddressSpace();
+
+  return getTargetInfo().getNullPointerValue(AS);
+}
+
 // Explicitly instantiate this in case a Redeclarable<T> is used from a TU that
 // doesn't include ASTContext.h
 template
diff --git a/lib/AST/ExprConstant.cpp b/lib/AST/ExprConstant.cpp
index e326510a10..949ec6382f 100644
--- a/lib/AST/ExprConstant.cpp
+++ b/lib/AST/ExprConstant.cpp
@@ -1070,6 +1070,7 @@ namespace {
     unsigned InvalidBase : 1;
     unsigned CallIndex : 31;
     SubobjectDesignator Designator;
+    bool IsNullPtr;
 
     const APValue::LValueBase getLValueBase() const { return Base; }
     CharUnits &getLValueOffset() { return Offset; }
@@ -1077,13 +1078,15 @@ namespace {
     unsigned getLValueCallIndex() const { return CallIndex; }
     SubobjectDesignator &getLValueDesignator() { return Designator; }
     const SubobjectDesignator &getLValueDesignator() const { return Designator;}
+    bool isNullPointer() const { return IsNullPtr;}
 
     void moveInto(APValue &V) const {
       if (Designator.Invalid)
-        V = APValue(Base, Offset, APValue::NoLValuePath(), CallIndex);
+        V = APValue(Base, Offset, APValue::NoLValuePath(), CallIndex,
+                    IsNullPtr);
       else
         V = APValue(Base, Offset, Designator.Entries,
-                    Designator.IsOnePastTheEnd, CallIndex);
+                    Designator.IsOnePastTheEnd, CallIndex, IsNullPtr);
     }
     void setFrom(ASTContext &Ctx, const APValue &V) {
       assert(V.isLValue());
@@ -1092,14 +1095,17 @@ namespace {
       InvalidBase = false;
       CallIndex = V.getLValueCallIndex();
       Designator = SubobjectDesignator(Ctx, V);
+      IsNullPtr = V.isNullPointer();
     }
 
-    void set(APValue::LValueBase B, unsigned I = 0, bool BInvalid = false) {
+    void set(APValue::LValueBase B, unsigned I = 0, bool BInvalid = false,
+             bool IsNullPtr_ = false, uint64_t Offset_ = 0) {
       Base = B;
-      Offset = CharUnits::Zero();
+      Offset = CharUnits::fromQuantity(Offset_);
       InvalidBase = BInvalid;
       CallIndex = I;
       Designator = SubobjectDesignator(getType(B));
+      IsNullPtr = IsNullPtr_;
     }
 
     void setInvalid(APValue::LValueBase B, unsigned I = 0) {
@@ -1112,7 +1118,7 @@ namespace {
                           CheckSubobjectKind CSK) {
       if (Designator.Invalid)
         return false;
-      if (!Base) {
+      if (IsNullPtr) {
         Info.CCEDiag(E, diag::note_constexpr_null_subobject)
           << CSK;
         Designator.setInvalid();
@@ -1141,9 +1147,22 @@ namespace {
       if (checkSubobject(Info, E, Imag ? CSK_Imag : CSK_Real))
         Designator.addComplexUnchecked(EltTy, Imag);
     }
-    void adjustIndex(EvalInfo &Info, const Expr *E, uint64_t N) {
-      if (N && checkNullPointer(Info, E, CSK_ArrayIndex))
-        Designator.adjustIndex(Info, E, N);
+    void clearIsNullPointer() {
+      IsNullPtr = false;
+    }
+    void adjustOffsetAndIndex(EvalInfo &Info, const Expr *E, uint64_t Index,
+                              CharUnits ElementSize) {
+      // Compute the new offset in the appropriate width.
+      Offset += Index * ElementSize;
+      if (Index && checkNullPointer(Info, E, CSK_ArrayIndex))
+        Designator.adjustIndex(Info, E, Index);
+      if (Index)
+        clearIsNullPointer();
+    }
+    void adjustOffset(CharUnits N) {
+      Offset += N;
+      if (N.getQuantity())
+        clearIsNullPointer();
     }
   };
 
@@ -2018,7 +2037,7 @@ static bool HandleLValueMember(EvalInfo &Info, const Expr *E, LValue &LVal,
   }
 
   unsigned I = FD->getFieldIndex();
-  LVal.Offset += Info.Ctx.toCharUnitsFromBits(RL->getFieldOffset(I));
+  LVal.adjustOffset(Info.Ctx.toCharUnitsFromBits(RL->getFieldOffset(I)));
   LVal.addDecl(Info, E, FD);
   return true;
 }
@@ -2072,9 +2091,7 @@ static bool HandleLValueArrayAdjustment(EvalInfo &Info, const Expr *E,
   if (!HandleSizeof(Info, E->getExprLoc(), EltTy, SizeOfPointee))
     return false;
 
-  // Compute the new offset in the appropriate width.
-  LVal.Offset += Adjustment * SizeOfPointee;
-  LVal.adjustIndex(Info, E, Adjustment);
+  LVal.adjustOffsetAndIndex(Info, E, Adjustment, SizeOfPointee);
   return true;
 }
 
@@ -5060,7 +5077,9 @@ public:
     return true;
   }
   bool ZeroInitialization(const Expr *E) {
-    return Success((Expr*)nullptr);
+    auto Offset = Info.Ctx.getTargetNullPointerValue(E->getType());
+    Result.set((Expr*)nullptr, 0, false, true, Offset);
+    return true;
   }
 
   bool VisitBinaryOperator(const BinaryOperator *E);
@@ -5159,6 +5178,8 @@ bool PointerExprEvaluator::VisitCastExpr(const CastExpr* E) {
       else
         CCEDiag(E, diag::note_constexpr_invalid_cast) << 2;
     }
+    if (E->getCastKind() == CK_AddressSpaceConversion && Result.IsNullPtr)
+      ZeroInitialization(E);
     return true;
 
   case CK_DerivedToBase:
@@ -5200,6 +5221,7 @@ bool PointerExprEvaluator::VisitCastExpr(const CastExpr* E) {
       Result.Offset = CharUnits::fromQuantity(N);
       Result.CallIndex = 0;
       Result.Designator.setInvalid();
+      Result.IsNullPtr = false;
       return true;
     } else {
       // Cast is of an lvalue, no need to change value.
@@ -8334,8 +8356,13 @@ bool IntExprEvaluator::VisitCastExpr(const CastExpr *E) {
       return true;
     }
 
-    APSInt AsInt = Info.Ctx.MakeIntValue(LV.getLValueOffset().getQuantity(), 
-                                         SrcType);
+    uint64_t V;
+    if (LV.isNullPointer())
+      V = Info.Ctx.getTargetNullPointerValue(SrcType);
+    else
+      V = LV.getLValueOffset().getQuantity();
+
+    APSInt AsInt = Info.Ctx.MakeIntValue(V, SrcType);
     return Success(HandleIntToIntCast(Info, E, DestType, SrcType, AsInt), E);
   }
 
diff --git a/lib/Basic/Targets.cpp b/lib/Basic/Targets.cpp
index 9a74cdf6f2..d80412a1e4 100644
--- a/lib/Basic/Targets.cpp
+++ b/lib/Basic/Targets.cpp
@@ -2245,6 +2245,13 @@ public:
         return CCCR_OK;
     }
   }
+
+  // In amdgcn target the null pointer in global, constant, and generic
+  // address space has value 0 but in private and local address space has
+  // value ~0.
+  uint64_t getNullPointerValue(unsigned AS) const override {
+    return AS != LangAS::opencl_local && AS != 0 ? 0 : ~0;
+  }
 };
 
 const Builtin::Info AMDGPUTargetInfo::BuiltinInfo[] = {
diff --git a/lib/CodeGen/CGDecl.cpp b/lib/CodeGen/CGDecl.cpp
index 695e92ea1d..4657347758 100644
--- a/lib/CodeGen/CGDecl.cpp
+++ b/lib/CodeGen/CGDecl.cpp
@@ -708,7 +708,7 @@ void CodeGenFunction::EmitScalarInit(const Expr *init, const ValueDecl *D,
     }
 
     auto ty = cast<llvm::PointerType>(tempLV.getAddress().getElementType());
-    llvm::Value *zero = llvm::ConstantPointerNull::get(ty);
+    llvm::Value *zero = CGM.getNullPointer(ty, tempLV.getType());
 
     // If __weak, we want to use a barrier under certain conditions.
     if (lifetime == Qualifiers::OCL_Weak)
diff --git a/lib/CodeGen/CGExprAgg.cpp b/lib/CodeGen/CGExprAgg.cpp
index 98f476efe9..c0989883e1 100644
--- a/lib/CodeGen/CGExprAgg.cpp
+++ b/lib/CodeGen/CGExprAgg.cpp
@@ -1050,7 +1050,8 @@ static bool isSimpleZero(const Expr *E, CodeGenFunction &CGF) {
     return true;
   // (int*)0 - Null pointer expressions.
   if (const CastExpr *ICE = dyn_cast<CastExpr>(E))
-    return ICE->getCastKind() == CK_NullToPointer;
+    return ICE->getCastKind() == CK_NullToPointer &&
+        CGF.getTypes().isPointerZeroInitializable(E->getType());
   // '\0'
   if (const CharacterLiteral *CL = dyn_cast<CharacterLiteral>(E))
     return CL->getValue() == 0;
diff --git a/lib/CodeGen/CGExprConstant.cpp b/lib/CodeGen/CGExprConstant.cpp
index 27c8386ee4..f657309177 100644
--- a/lib/CodeGen/CGExprConstant.cpp
+++ b/lib/CodeGen/CGExprConstant.cpp
@@ -16,6 +16,7 @@
 #include "CGObjCRuntime.h"
 #include "CGRecordLayout.h"
 #include "CodeGenModule.h"
+#include "TargetInfo.h"
 #include "clang/AST/APValue.h"
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/RecordLayout.h"
@@ -1262,6 +1263,10 @@ llvm::Constant *CodeGenModule::EmitConstantExpr(const Expr *E,
   return C;
 }
 
+llvm::Constant *CodeGenModule::getNullPointer(llvm::PointerType *T, QualType QT) {
+  return getTargetCodeGenInfo().getNullPointer(*this, T, QT);
+}
+
 llvm::Constant *CodeGenModule::EmitConstantValue(const APValue &Value,
                                                  QualType DestType,
                                                  CodeGenFunction *CGF) {
@@ -1293,6 +1298,7 @@ llvm::Constant *CodeGenModule::EmitConstantValue(const APValue &Value,
       llvm::ConstantInt::get(Int64Ty, Value.getLValueOffset().getQuantity());
 
     llvm::Constant *C = nullptr;
+
     if (APValue::LValueBase LVBase = Value.getLValueBase()) {
       // An array can be represented as an lvalue referring to the base.
       if (isa<llvm::ArrayType>(DestTy)) {
@@ -1323,7 +1329,9 @@ llvm::Constant *CodeGenModule::EmitConstantValue(const APValue &Value,
 
       // Convert to the appropriate type; this could be an lvalue for
       // an integer.
-      if (isa<llvm::PointerType>(DestTy)) {
+      if (auto PT = dyn_cast<llvm::PointerType>(DestTy)) {
+        if (Value.isNullPointer())
+          return getNullPointer(PT, DestType);
         // Convert the integer to a pointer-sized integer before converting it
         // to a pointer.
         C = llvm::ConstantExpr::getIntegerCast(
@@ -1510,7 +1518,7 @@ static llvm::Constant *EmitNullConstantForBase(CodeGenModule &CGM,
                                                const CXXRecordDecl *base);
 
 static llvm::Constant *EmitNullConstant(CodeGenModule &CGM,
-                                        const CXXRecordDecl *record,
+                                        const RecordDecl *record,
                                         bool asCompleteObject) {
   const CGRecordLayout &layout = CGM.getTypes().getCGRecordLayout(record);
   llvm::StructType *structure =
@@ -1520,25 +1528,29 @@ static llvm::Constant *EmitNullConstant(CodeGenModule &CGM,
   unsigned numElements = structure->getNumElements();
   std::vector<llvm::Constant *> elements(numElements);
 
+  auto CXXR = dyn_cast<CXXRecordDecl>(record);
   // Fill in all the bases.
-  for (const auto &I : record->bases()) {
-    if (I.isVirtual()) {
-      // Ignore virtual bases; if we're laying out for a complete
-      // object, we'll lay these out later.
-      continue;
-    }
+  if (CXXR) {
+    for (const auto &I : CXXR->bases()) {
+      if (I.isVirtual()) {
+        // Ignore virtual bases; if we're laying out for a complete
+        // object, we'll lay these out later.
+        continue;
+      }
 
-    const CXXRecordDecl *base = 
-      cast<CXXRecordDecl>(I.getType()->castAs<RecordType>()->getDecl());
+      const CXXRecordDecl *base =
+        cast<CXXRecordDecl>(I.getType()->castAs<RecordType>()->getDecl());
 
-    // Ignore empty bases.
-    if (base->isEmpty() ||
-        CGM.getContext().getASTRecordLayout(base).getNonVirtualSize().isZero())
-      continue;
-    
-    unsigned fieldIndex = layout.getNonVirtualBaseLLVMFieldNo(base);
-    llvm::Type *baseType = structure->getElementType(fieldIndex);
-    elements[fieldIndex] = EmitNullConstantForBase(CGM, baseType, base);
+      // Ignore empty bases.
+      if (base->isEmpty() ||
+          CGM.getContext().getASTRecordLayout(base).getNonVirtualSize()
+              .isZero())
+        continue;
+
+      unsigned fieldIndex = layout.getNonVirtualBaseLLVMFieldNo(base);
+      llvm::Type *baseType = structure->getElementType(fieldIndex);
+      elements[fieldIndex] = EmitNullConstantForBase(CGM, baseType, base);
+    }
   }
 
   // Fill in all the fields.
@@ -1562,8 +1574,8 @@ static llvm::Constant *EmitNullConstant(CodeGenModule &CGM,
   }
 
   // Fill in the virtual bases, if we're working with the complete object.
-  if (asCompleteObject) {
-    for (const auto &I : record->vbases()) {
+  if (CXXR && asCompleteObject) {
+    for (const auto &I : CXXR->vbases()) {
       const CXXRecordDecl *base = 
         cast<CXXRecordDecl>(I.getType()->castAs<RecordType>()->getDecl());
 
@@ -1605,6 +1617,10 @@ static llvm::Constant *EmitNullConstantForBase(CodeGenModule &CGM,
 }
 
 llvm::Constant *CodeGenModule::EmitNullConstant(QualType T) {
+  if (auto PT = T->getAs<PointerType>())
+    return getNullPointer(cast<llvm::PointerType>(getTypes().ConvertTypeForMem(T)),
+                      T);
+
   if (getTypes().isZeroInitializable(T))
     return llvm::Constant::getNullValue(getTypes().ConvertTypeForMem(T));
     
@@ -1620,10 +1636,8 @@ llvm::Constant *CodeGenModule::EmitNullConstant(QualType T) {
     return llvm::ConstantArray::get(ATy, Array);
   }
 
-  if (const RecordType *RT = T->getAs<RecordType>()) {
-    const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
-    return ::EmitNullConstant(*this, RD, /*complete object*/ true);
-  }
+  if (const RecordType *RT = T->getAs<RecordType>())
+    return ::EmitNullConstant(*this, RT->getDecl(), /*complete object*/ true);
 
   assert(T->isMemberDataPointerType() &&
          "Should only see pointers to data members here!");
diff --git a/lib/CodeGen/CGExprScalar.cpp b/lib/CodeGen/CGExprScalar.cpp
index dc8186563c..2b54370c29 100644
--- a/lib/CodeGen/CGExprScalar.cpp
+++ b/lib/CodeGen/CGExprScalar.cpp
@@ -19,6 +19,7 @@
 #include "TargetInfo.h"
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/DeclObjC.h"
+#include "clang/AST/Expr.h"
 #include "clang/AST/RecordLayout.h"
 #include "clang/AST/StmtVisitor.h"
 #include "clang/Basic/TargetInfo.h"
@@ -171,9 +172,9 @@ public:
   }
 
   /// EmitPointerToBoolConversion - Perform a pointer to boolean conversion.
-  Value *EmitPointerToBoolConversion(Value *V) {
-    Value *Zero = llvm::ConstantPointerNull::get(
-                                      cast<llvm::PointerType>(V->getType()));
+  Value *EmitPointerToBoolConversion(Value *V, QualType QT) {
+    Value *Zero = CGF.CGM.getNullPointer(cast<llvm::PointerType>(V->getType()), QT);
+
     return Builder.CreateICmpNE(V, Zero, "tobool");
   }
 
@@ -591,7 +592,7 @@ Value *ScalarExprEmitter::EmitConversionToBool(Value *Src, QualType SrcType) {
     return EmitIntToBoolConversion(Src);
 
   assert(isa<llvm::PointerType>(Src->getType()));
-  return EmitPointerToBoolConversion(Src);
+  return EmitPointerToBoolConversion(Src, SrcType);
 }
 
 void ScalarExprEmitter::EmitFloatConversionCheck(
@@ -1394,11 +1395,23 @@ Value *ScalarExprEmitter::VisitCastExpr(CastExpr *CE) {
     return Builder.CreateBitCast(Src, DstTy);
   }
   case CK_AddressSpaceConversion: {
-    Value *Src = Visit(const_cast<Expr*>(E));
+    Expr::EvalResult Result;
+    if (E->EvaluateAsRValue(Result, CGF.getContext()) &&
+        Result.Val.isNullPointer()) {
+      // If E has side effect, it is emitted even if its final result is a
+      // null pointer. In that case, a DCE pass should be able to
+      // eliminate the useless instructions emitted during translating E.
+      if (Result.HasSideEffects)
+        Visit(E);
+      return CGF.CGM.getNullPointer(cast<llvm::PointerType>(
+          ConvertType(DestTy)), DestTy);
+    }
     // Since target may map different address spaces in AST to the same address
     // space, an address space conversion may end up as a bitcast.
-    return Builder.CreatePointerBitCastOrAddrSpaceCast(Src,
-                                                       ConvertType(DestTy));
+    auto *Src = Visit(E);
+    return CGF.CGM.getTargetCodeGenInfo().performAddrSpaceCast(CGF, Src,
+                                                               E->getType(),
+                                                               DestTy);
   }
   case CK_AtomicToNonAtomic:
   case CK_NonAtomicToAtomic:
@@ -1453,8 +1466,8 @@ Value *ScalarExprEmitter::VisitCastExpr(CastExpr *CE) {
     if (MustVisitNullValue(E))
       (void) Visit(E);
 
-    return llvm::ConstantPointerNull::get(
-                               cast<llvm::PointerType>(ConvertType(DestTy)));
+    return CGF.CGM.getNullPointer(cast<llvm::PointerType>(ConvertType(DestTy)),
+                              DestTy);
 
   case CK_NullToMemberPointer: {
     if (MustVisitNullValue(E))
@@ -1547,7 +1560,7 @@ Value *ScalarExprEmitter::VisitCastExpr(CastExpr *CE) {
   case CK_IntegralToBoolean:
     return EmitIntToBoolConversion(Visit(E));
   case CK_PointerToBoolean:
-    return EmitPointerToBoolConversion(Visit(E));
+    return EmitPointerToBoolConversion(Visit(E), E->getType());
   case CK_FloatingToBoolean:
     return EmitFloatToBoolConversion(Visit(E));
   case CK_MemberPointerToBoolean: {
diff --git a/lib/CodeGen/CodeGenModule.cpp b/lib/CodeGen/CodeGenModule.cpp
index 78f43bdef9..98b6215d0b 100644
--- a/lib/CodeGen/CodeGenModule.cpp
+++ b/lib/CodeGen/CodeGenModule.cpp
@@ -2611,9 +2611,16 @@ void CodeGenModule::EmitGlobalVarDefinition(const VarDecl *D,
   else
     GV->setDLLStorageClass(llvm::GlobalVariable::DefaultStorageClass);
 
-  if (Linkage == llvm::GlobalVariable::CommonLinkage)
+  if (Linkage == llvm::GlobalVariable::CommonLinkage) {
     // common vars aren't constant even if declared const.
     GV->setConstant(false);
+    // Tentative definition of global variables may be initialized with
+    // non-zero null pointers. In this case they should have weak linkage
+    // since common linkage must have zero initializer and must not have
+    // explicit section therefore cannot have non-zero initial value.
+    if (!GV->getInitializer()->isNullValue())
+      GV->setLinkage(llvm::GlobalVariable::WeakAnyLinkage);
+  }
 
   setNonAliasAttributes(D, GV);
 
diff --git a/lib/CodeGen/CodeGenModule.h b/lib/CodeGen/CodeGenModule.h
index be45bb8ea4..f014be9557 100644
--- a/lib/CodeGen/CodeGenModule.h
+++ b/lib/CodeGen/CodeGenModule.h
@@ -1155,6 +1155,11 @@ public:
   llvm::Value *
   createOpenCLIntToSamplerConversion(const Expr *E, CodeGenFunction &CGF);
 
+  /// Get target specific null pointer.
+  /// \param T is the LLVM type of the null pointer.
+  /// \param QT is the clang QualType of the null pointer.
+  llvm::Constant *getNullPointer(llvm::PointerType *T, QualType QT);
+
 private:
   llvm::Constant *
   GetOrCreateLLVMFunction(StringRef MangledName, llvm::Type *Ty, GlobalDecl D,
diff --git a/lib/CodeGen/CodeGenTypes.cpp b/lib/CodeGen/CodeGenTypes.cpp
index ebe55c70d8..1ec6607ccc 100644
--- a/lib/CodeGen/CodeGenTypes.cpp
+++ b/lib/CodeGen/CodeGenTypes.cpp
@@ -736,10 +736,14 @@ CodeGenTypes::getCGRecordLayout(const RecordDecl *RD) {
   return *Layout;
 }
 
+bool CodeGenTypes::isPointerZeroInitializable(QualType T) {
+  assert (T->getAs<PointerType>() && "Invalid type");
+  return isZeroInitializable(T);
+}
+
 bool CodeGenTypes::isZeroInitializable(QualType T) {
-  // No need to check for member pointers when not compiling C++.
-  if (!Context.getLangOpts().CPlusPlus)
-    return true;
+  if (auto PT = T->getAs<PointerType>())
+    return Context.getTargetNullPointerValue(T) == 0;
 
   if (const auto *AT = Context.getAsArrayType(T)) {
     if (isa<IncompleteArrayType>(AT))
@@ -753,7 +757,7 @@ bool CodeGenTypes::isZeroInitializable(QualType T) {
   // Records are non-zero-initializable if they contain any
   // non-zero-initializable subobjects.
   if (const RecordType *RT = T->getAs<RecordType>()) {
-    const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
+    auto RD = cast<RecordDecl>(RT->getDecl());
     return isZeroInitializable(RD);
   }
 
diff --git a/lib/CodeGen/CodeGenTypes.h b/lib/CodeGen/CodeGenTypes.h
index 00df10dd13..2ce6591e4e 100644
--- a/lib/CodeGen/CodeGenTypes.h
+++ b/lib/CodeGen/CodeGenTypes.h
@@ -352,6 +352,10 @@ public:  // These are internal details of CGT that shouldn't be used externally.
   /// zero-initialized (in the C++ sense) with an LLVM zeroinitializer.
   bool isZeroInitializable(QualType T);
 
+  /// Check if the pointer type can be zero-initialized (in the C++ sense)
+  /// with an LLVM zeroinitializer.
+  bool isPointerZeroInitializable(QualType T);
+
   /// IsZeroInitializable - Return whether a record type can be
   /// zero-initialized (in the C++ sense) with an LLVM zeroinitializer.
   bool isZeroInitializable(const RecordDecl *RD);
diff --git a/lib/CodeGen/TargetInfo.cpp b/lib/CodeGen/TargetInfo.cpp
index 79d481580e..f70c6cb5de 100644
--- a/lib/CodeGen/TargetInfo.cpp
+++ b/lib/CodeGen/TargetInfo.cpp
@@ -401,6 +401,20 @@ unsigned TargetCodeGenInfo::getOpenCLKernelCallingConv() const {
   return llvm::CallingConv::C;
 }
 
+llvm::Constant *TargetCodeGenInfo::getNullPointer(const CodeGen::CodeGenModule &CGM,
+    llvm::PointerType *T, QualType QT) const {
+  return llvm::ConstantPointerNull::get(T);
+}
+
+llvm::Value *TargetCodeGenInfo::performAddrSpaceCast(
+    CodeGen::CodeGenFunction &CGF, llvm::Value *Src, QualType SrcTy,
+    QualType DestTy) const {
+  // Since target may map different address spaces in AST to the same address
+  // space, an address space conversion may end up as a bitcast.
+  return CGF.Builder.CreatePointerBitCastOrAddrSpaceCast(Src,
+             CGF.ConvertType(DestTy));
+}
+
 static bool isEmptyRecord(ASTContext &Context, QualType T, bool AllowArrays);
 
 /// isEmptyField - Return true iff a the field is "empty", that is it
@@ -7075,8 +7089,10 @@ public:
   void setTargetAttributes(const Decl *D, llvm::GlobalValue *GV,
                            CodeGen::CodeGenModule &M) const override;
   unsigned getOpenCLKernelCallingConv() const override;
-};
 
+  llvm::Constant *getNullPointer(const CodeGen::CodeGenModule &CGM,
+      llvm::PointerType *T, QualType QT) const override;
+};
 }
 
 static void appendOpenCLVersionMD (CodeGen::CodeGenModule &CGM);
@@ -7140,6 +7156,24 @@ unsigned AMDGPUTargetCodeGenInfo::getOpenCLKernelCallingConv() const {
   return llvm::CallingConv::AMDGPU_KERNEL;
 }
 
+// Currently LLVM assumes null pointers always have value 0,
+// which results in incorrectly transformed IR. Therefore, instead of
+// emitting null pointers in private and local address spaces, a null
+// pointer in generic address space is emitted which is casted to a
+// pointer in local or private address space.
+llvm::Constant *AMDGPUTargetCodeGenInfo::getNullPointer(
+    const CodeGen::CodeGenModule &CGM, llvm::PointerType *PT,
+    QualType QT) const {
+  if (CGM.getContext().getTargetNullPointerValue(QT) == 0)
+    return llvm::ConstantPointerNull::get(PT);
+
+  auto &Ctx = CGM.getContext();
+  auto NPT = llvm::PointerType::get(PT->getElementType(),
+      Ctx.getTargetAddressSpace(LangAS::opencl_generic));
+  return llvm::ConstantExpr::getAddrSpaceCast(
+      llvm::ConstantPointerNull::get(NPT), PT);
+}
+
 //===----------------------------------------------------------------------===//
 // SPARC v8 ABI Implementation.
 // Based on the SPARC Compliance Definition version 2.4.1.
diff --git a/lib/CodeGen/TargetInfo.h b/lib/CodeGen/TargetInfo.h
index e46382596a..223d6d047a 100644
--- a/lib/CodeGen/TargetInfo.h
+++ b/lib/CodeGen/TargetInfo.h
@@ -220,6 +220,22 @@ public:
 
   /// Get LLVM calling convention for OpenCL kernel.
   virtual unsigned getOpenCLKernelCallingConv() const;
+
+  /// Get target specific null pointer.
+  /// \param T is the LLVM type of the null pointer.
+  /// \param QT is the clang QualType of the null pointer.
+  /// \return ConstantPointerNull with the given type \p T.
+  /// Each target can override it to return its own desired constant value.
+  virtual llvm::Constant *getNullPointer(const CodeGen::CodeGenModule &CGM,
+      llvm::PointerType *T, QualType QT) const;
+
+  /// Perform address space cast of an expression of pointer type.
+  /// \param V is the LLVM value to be casted to another address space.
+  /// \param SrcTy is the QualType of \p V.
+  /// \param DestTy is the destination QualType.
+  virtual llvm::Value *performAddrSpaceCast(CodeGen::CodeGenFunction &CGF,
+      llvm::Value *V, QualType SrcTy, QualType DestTy) const;
+
 };
 
 } // namespace CodeGen
diff --git a/test/CodeGenOpenCL/amdgpu-nullptr.cl b/test/CodeGenOpenCL/amdgpu-nullptr.cl
new file mode 100644
index 0000000000..2d36fa90a6
--- /dev/null
+++ b/test/CodeGenOpenCL/amdgpu-nullptr.cl
@@ -0,0 +1,534 @@
+// RUN: %clang_cc1 %s -cl-std=CL2.0 -include opencl-c.h -triple amdgcn -emit-llvm -o - | FileCheck %s
+// RUN: %clang_cc1 %s -O0 -cl-std=CL2.0 -include opencl-c.h -triple amdgcn -emit-llvm -o - | FileCheck --check-prefix=NOOPT %s
+
+typedef struct {
+  private char *p1;
+  local char *p2;
+  constant char *p3;
+  global char *p4;
+  generic char *p5;
+} StructTy1;
+
+typedef struct {
+  constant char *p3;
+  global char *p4;
+  generic char *p5;
+} StructTy2;
+
+// LLVM requests global variable with common linkage to be initialized with zeroinitializer, therefore use -fno-common
+// to suppress common linkage for tentative definition.
+
+// Test 0 as initializer.
+
+// CHECK: @private_p = local_unnamed_addr addrspace(1) global i8* addrspacecast (i8 addrspace(4)* null to i8*), align 4
+private char *private_p = 0;
+
+// CHECK: @local_p = local_unnamed_addr addrspace(1) global i8 addrspace(3)* addrspacecast (i8 addrspace(4)* null to i8 addrspace(3)*), align 4
+local char *local_p = 0;
+
+// CHECK: @global_p = local_unnamed_addr addrspace(1) global i8 addrspace(1)* null, align 4
+global char *global_p = 0;
+
+// CHECK: @constant_p = local_unnamed_addr addrspace(1) global i8 addrspace(2)* null, align 4
+constant char *constant_p = 0;
+
+// CHECK: @generic_p = local_unnamed_addr addrspace(1) global i8 addrspace(4)* null, align 4
+generic char *generic_p = 0;
+
+// Test NULL as initializer.
+
+// CHECK: @private_p_NULL = local_unnamed_addr addrspace(1) global i8* addrspacecast (i8 addrspace(4)* null to i8*), align 4
+private char *private_p_NULL = NULL;
+
+// CHECK: @local_p_NULL = local_unnamed_addr addrspace(1) global i8 addrspace(3)* addrspacecast (i8 addrspace(4)* null to i8 addrspace(3)*), align 4
+local char *local_p_NULL = NULL;
+
+// CHECK: @global_p_NULL = local_unnamed_addr addrspace(1) global i8 addrspace(1)* null, align 4
+global char *global_p_NULL = NULL;
+
+// CHECK: @constant_p_NULL = local_unnamed_addr addrspace(1) global i8 addrspace(2)* null, align 4
+constant char *constant_p_NULL = NULL;
+
+// CHECK: @generic_p_NULL = local_unnamed_addr addrspace(1) global i8 addrspace(4)* null, align 4
+generic char *generic_p_NULL = NULL;
+
+// Test constant folding of null pointer.
+// A null pointer should be folded to a null pointer in the target address space.
+
+// CHECK: @fold_generic = local_unnamed_addr addrspace(1) global i32 addrspace(4)* null, align 4
+generic int *fold_generic = (global int*)(generic float*)(private char*)0;
+
+// CHECK: @fold_priv = local_unnamed_addr addrspace(1) global i16* addrspacecast (i16 addrspace(4)* null to i16*), align 4
+private short *fold_priv = (private short*)(generic int*)(global void*)0;
+
+// CHECK: @fold_priv_arith = local_unnamed_addr addrspace(1) global i8* inttoptr (i32 9 to i8*), align 4
+private char *fold_priv_arith = (private char*)0 + 10;
+
+// CHECK: @fold_int = local_unnamed_addr addrspace(1) global i32 13, align 4
+int fold_int = (int)(private void*)(generic char*)(global int*)0 + 14;
+
+// CHECK: @fold_int2 = local_unnamed_addr addrspace(1) global i32 12, align 4
+int fold_int2 = (int) ((private void*)0 + 13);
+
+// CHECK: @fold_int3 = local_unnamed_addr addrspace(1) global i32 -1, align 4
+int fold_int3 = (int) ((private int*)0);
+
+// CHECK: @fold_int4 = local_unnamed_addr addrspace(1) global i32 7, align 4
+int fold_int4 = (int) &((private int*)0)[2];
+
+// CHECK: @fold_int5 = local_unnamed_addr addrspace(1) global i32 3, align 4
+int fold_int5 = (int) &((private StructTy1*)0)->p2;
+
+// Test static variable initialization.
+
+// NOOPT: @test_static_var.sp1 = internal addrspace(1) global i8* addrspacecast (i8 addrspace(4)* null to i8*), align 4
+// NOOPT: @test_static_var.sp2 = internal addrspace(1) global i8* addrspacecast (i8 addrspace(4)* null to i8*), align 4
+// NOOPT: @test_static_var.sp3 = internal addrspace(1) global i8* addrspacecast (i8 addrspace(4)* null to i8*), align 4
+// NOOPT: @test_static_var.sp4 = internal addrspace(1) global i8* null, align 4
+// NOOPT: @test_static_var.sp5 = internal addrspace(1) global i8* null, align 4
+// NOOPT: @test_static_var.SS1 = internal addrspace(1) global %struct.StructTy1 { i8* addrspacecast (i8 addrspace(4)* null to i8*), i8 addrspace(3)* addrspacecast (i8 addrspace(4)* null to i8 addrspace(3)*), i8 addrspace(2)* null, i8 addrspace(1)* null, i8 addrspace(4)* null }, align 4
+// NOOPT: @test_static_var.SS2 = internal addrspace(1) global %struct.StructTy2 zeroinitializer, align 4
+
+void test_static_var(void) {
+  static private char *sp1 = 0;
+  static private char *sp2 = NULL;
+  static private char *sp3;
+  static private char *sp4 = (private char*)((void)0, 0);
+  const int x = 0;
+  static private char *sp5 = (private char*)x;
+  static StructTy1 SS1;
+  static StructTy2 SS2;
+}
+
+// Test function-scope variable initialization.
+// NOOPT-LABEL: test_func_scope_var
+// NOOPT: store i8* addrspacecast (i8 addrspace(4)* null to i8*), i8** %sp1, align 4
+// NOOPT: store i8* addrspacecast (i8 addrspace(4)* null to i8*), i8** %sp2, align 4
+// NOOPT: store i8* null, i8** %sp3, align 4
+// NOOPT: store i8* null, i8** %sp4, align 4
+// NOOPT: %[[SS1:.*]] = bitcast %struct.StructTy1* %SS1 to i8*
+// NOOPT: call void @llvm.memcpy.p0i8.p2i8.i64(i8* %[[SS1]], i8 addrspace(2)* bitcast (%struct.StructTy1 addrspace(2)* @test_func_scope_var.SS1 to i8 addrspace(2)*), i64 32, i32 4, i1 false)
+// NOOPT: %[[SS2:.*]] = bitcast %struct.StructTy2* %SS2 to i8*
+// NOOPT: call void @llvm.memset.p0i8.i64(i8* %[[SS2]], i8 0, i64 24, i32 4, i1 false)
+
+void test_func_scope_var(void) {
+  private char *sp1 = 0;
+  private char *sp2 = NULL;
+  private char *sp3 = (private char*)((void)0, 0);
+  const int x = 0;
+  private char *sp4 = (private char*)x;
+  StructTy1 SS1 = {0, 0, 0, 0, 0};
+  StructTy2 SS2 = {0, 0, 0};
+}
+
+// Test default initialization of pointers.
+
+// Tentative definition of global variables with non-zero initializer
+// cannot have common linkage since common linkage requires zero initialization
+// and does not have explicit section.
+
+// CHECK: @p1 = weak local_unnamed_addr addrspace(1) global i8* addrspacecast (i8 addrspace(4)* null to i8*), align 4
+private char *p1;
+
+// CHECK: @p2 = weak local_unnamed_addr addrspace(1) global i8 addrspace(3)* addrspacecast (i8 addrspace(4)* null to i8 addrspace(3)*), align 4
+local char *p2;
+
+// CHECK: @p3 = common local_unnamed_addr addrspace(1) global i8 addrspace(2)* null, align 4
+constant char *p3;
+
+// CHECK: @p4 = common local_unnamed_addr addrspace(1) global i8 addrspace(1)* null, align 4
+global char *p4;
+
+// CHECK: @p5 = common local_unnamed_addr addrspace(1) global i8 addrspace(4)* null, align 4
+generic char *p5;
+
+// Test default initialization of sturcture.
+
+// CHECK: @S1 = weak local_unnamed_addr addrspace(1) global %struct.StructTy1 { i8* addrspacecast (i8 addrspace(4)* null to i8*), i8 addrspace(3)* addrspacecast (i8 addrspace(4)* null to i8 addrspace(3)*), i8 addrspace(2)* null, i8 addrspace(1)* null, i8 addrspace(4)* null }, align 4
+StructTy1 S1;
+
+// CHECK: @S2 = common local_unnamed_addr addrspace(1) global %struct.StructTy2 zeroinitializer, align 4
+StructTy2 S2;
+
+// Test default initialization of array.
+// CHECK: @A1 = weak local_unnamed_addr addrspace(1) global [2 x %struct.StructTy1] [%struct.StructTy1 { i8* addrspacecast (i8 addrspace(4)* null to i8*), i8 addrspace(3)* addrspacecast (i8 addrspace(4)* null to i8 addrspace(3)*), i8 addrspace(2)* null, i8 addrspace(1)* null, i8 addrspace(4)* null }, %struct.StructTy1 { i8* addrspacecast (i8 addrspace(4)* null to i8*), i8 addrspace(3)* addrspacecast (i8 addrspace(4)* null to i8 addrspace(3)*), i8 addrspace(2)* null, i8 addrspace(1)* null, i8 addrspace(4)* null }], align 4
+StructTy1 A1[2];
+
+// CHECK: @A2 = common local_unnamed_addr addrspace(1) global [2 x %struct.StructTy2] zeroinitializer, align 4
+StructTy2 A2[2];
+
+// Test comparison with 0.
+
+// CHECK-LABEL: cmp_private
+// CHECK: icmp eq i8* %p, addrspacecast (i8 addrspace(4)* null to i8*)
+void cmp_private(private char* p) {
+  if (p != 0)
+    *p = 0;
+}
+
+// CHECK-LABEL: cmp_local
+// CHECK: icmp eq i8 addrspace(3)* %p, addrspacecast (i8 addrspace(4)* null to i8 addrspace(3)*)
+void cmp_local(local char* p) {
+  if (p != 0)
+    *p = 0;
+}
+
+// CHECK-LABEL: cmp_global
+// CHECK: icmp eq i8 addrspace(1)* %p, null
+void cmp_global(global char* p) {
+  if (p != 0)
+    *p = 0;
+}
+
+// CHECK-LABEL: cmp_constant
+// CHECK: icmp eq i8 addrspace(2)* %p, null
+char cmp_constant(constant char* p) {
+  if (p != 0)
+    return *p;
+  else
+    return 0;
+}
+
+// CHECK-LABEL: cmp_generic
+// CHECK: icmp eq i8 addrspace(4)* %p, null
+void cmp_generic(generic char* p) {
+  if (p != 0)
+    *p = 0;
+}
+
+// Test comparison with NULL.
+
+// CHECK-LABEL: cmp_NULL_private
+// CHECK: icmp eq i8* %p, addrspacecast (i8 addrspace(4)* null to i8*)
+void cmp_NULL_private(private char* p) {
+  if (p != NULL)
+    *p = 0;
+}
+
+// CHECK-LABEL: cmp_NULL_local
+// CHECK: icmp eq i8 addrspace(3)* %p, addrspacecast (i8 addrspace(4)* null to i8 addrspace(3)*)
+void cmp_NULL_local(local char* p) {
+  if (p != NULL)
+    *p = 0;
+}
+
+// CHECK-LABEL: cmp_NULL_global
+// CHECK: icmp eq i8 addrspace(1)* %p, null
+void cmp_NULL_global(global char* p) {
+  if (p != NULL)
+    *p = 0;
+}
+
+// CHECK-LABEL: cmp_NULL_constant
+// CHECK: icmp eq i8 addrspace(2)* %p, null
+char cmp_NULL_constant(constant char* p) {
+  if (p != NULL)
+    return *p;
+  else
+    return 0;
+}
+
+// CHECK-LABEL: cmp_NULL_generic
+// CHECK: icmp eq i8 addrspace(4)* %p, null
+void cmp_NULL_generic(generic char* p) {
+  if (p != NULL)
+    *p = 0;
+}
+
+// Test storage 0 as null pointer.
+// CHECK-LABEL: test_storage_null_pointer
+// CHECK: store i8* addrspacecast (i8 addrspace(4)* null to i8*), i8* addrspace(4)* %arg_private
+// CHECK: store i8 addrspace(3)* addrspacecast (i8 addrspace(4)* null to i8 addrspace(3)*), i8 addrspace(3)* addrspace(4)* %arg_local
+// CHECK: store i8 addrspace(1)* null, i8 addrspace(1)* addrspace(4)* %arg_global
+// CHECK: store i8 addrspace(2)* null, i8 addrspace(2)* addrspace(4)* %arg_constant
+// CHECK: store i8 addrspace(4)* null, i8 addrspace(4)* addrspace(4)* %arg_generic
+void test_storage_null_pointer(private char** arg_private,
+                               local char** arg_local,
+                               global char** arg_global,
+                               constant char** arg_constant,
+                               generic char** arg_generic) {
+   *arg_private = 0;
+   *arg_local = 0;
+   *arg_global = 0;
+   *arg_constant = 0;
+   *arg_generic = 0;
+}
+
+// Test storage NULL as null pointer.
+// CHECK-LABEL: test_storage_null_pointer_NULL
+// CHECK: store i8* addrspacecast (i8 addrspace(4)* null to i8*), i8* addrspace(4)* %arg_private
+// CHECK: store i8 addrspace(3)* addrspacecast (i8 addrspace(4)* null to i8 addrspace(3)*), i8 addrspace(3)* addrspace(4)* %arg_local
+// CHECK: store i8 addrspace(1)* null, i8 addrspace(1)* addrspace(4)* %arg_global
+// CHECK: store i8 addrspace(2)* null, i8 addrspace(2)* addrspace(4)* %arg_constant
+// CHECK: store i8 addrspace(4)* null, i8 addrspace(4)* addrspace(4)* %arg_generic
+void test_storage_null_pointer_NULL(private char** arg_private,
+                                    local char** arg_local,
+                                    global char** arg_global,
+                                    constant char** arg_constant,
+                                    generic char** arg_generic) {
+   *arg_private = NULL;
+   *arg_local = NULL;
+   *arg_global = NULL;
+   *arg_constant = NULL;
+   *arg_generic = NULL;
+}
+
+// Test pass null pointer to function as argument.
+void test_pass_null_pointer_arg_calee(private char* arg_private,
+                                      local char* arg_local,
+                                      global char* arg_global,
+                                      constant char* arg_constant,
+                                      generic char* arg_generic);
+
+// CHECK-LABEL: test_pass_null_pointer_arg
+// CHECK: call void @test_pass_null_pointer_arg_calee(i8* addrspacecast (i8 addrspace(4)* null to i8*), i8 addrspace(3)* addrspacecast (i8 addrspace(4)* null to i8 addrspace(3)*), i8 addrspace(1)* null, i8 addrspace(2)* null, i8 addrspace(4)* null)
+// CHECK: call void @test_pass_null_pointer_arg_calee(i8* addrspacecast (i8 addrspace(4)* null to i8*), i8 addrspace(3)* addrspacecast (i8 addrspace(4)* null to i8 addrspace(3)*), i8 addrspace(1)* null, i8 addrspace(2)* null, i8 addrspace(4)* null)
+void test_pass_null_pointer_arg(void) {
+  test_pass_null_pointer_arg_calee(0, 0, 0, 0, 0);
+  test_pass_null_pointer_arg_calee(NULL, NULL, NULL, NULL, NULL);
+}
+
+// Test cast null pointer to size_t.
+void test_cast_null_pointer_to_sizet_calee(size_t arg_private,
+                                           size_t arg_local,
+                                           size_t arg_global,
+                                           size_t arg_constant,
+                                           size_t arg_generic);
+
+// CHECK-LABEL: test_cast_null_pointer_to_sizet
+// CHECK: call void @test_cast_null_pointer_to_sizet_calee(i64 ptrtoint (i8* addrspacecast (i8 addrspace(4)* null to i8*) to i64), i64 ptrtoint (i8 addrspace(3)* addrspacecast (i8 addrspace(4)* null to i8 addrspace(3)*) to i64), i64 0, i64 0, i64 0)
+// CHECK: call void @test_cast_null_pointer_to_sizet_calee(i64 ptrtoint (i8* addrspacecast (i8 addrspace(4)* null to i8*) to i64), i64 ptrtoint (i8 addrspace(3)* addrspacecast (i8 addrspace(4)* null to i8 addrspace(3)*) to i64), i64 0, i64 0, i64 0)
+void test_cast_null_pointer_to_sizet(void) {
+  test_cast_null_pointer_to_sizet_calee((size_t)((private char*)0),
+                                        (size_t)((local char*)0),
+                                        (size_t)((global char*)0),
+                                        (size_t)((constant char*)0),
+                                        (size_t)((generic char*)0));
+  test_cast_null_pointer_to_sizet_calee((size_t)((private char*)NULL),
+                                        (size_t)((local char*)NULL),
+                                        (size_t)((global char*)NULL),
+                                        (size_t)((constant char*)0), // NULL cannot be casted to constant pointer since it is defined as a generic pointer
+                                        (size_t)((generic char*)NULL));
+}
+
+// Test comparision between null pointers.
+#define TEST_EQ00(addr1, addr2) int test_eq00_##addr1##_##addr2(void) { return (addr1 char*)0 == (addr2 char*)0; }
+#define TEST_EQ0N(addr1, addr2) int test_eq0N_##addr1##_##addr2(void) { return (addr1 char*)0 == (addr2 char*)NULL; }
+#define TEST_EQN0(addr1, addr2) int test_eqN0_##addr1##_##addr2(void) { return (addr1 char*)NULL == (addr2 char*)0; }
+#define TEST_EQNN(addr1, addr2) int test_eqNN_##addr1##_##addr2(void) { return (addr1 char*)0 == (addr2 char*)NULL; }
+#define TEST_NE00(addr1, addr2) int test_ne00_##addr1##_##addr2(void) { return (addr1 char*)0 != (addr2 char*)0; }
+#define TEST_NE0N(addr1, addr2) int test_ne0N_##addr1##_##addr2(void) { return (addr1 char*)0 != (addr2 char*)NULL; }
+#define TEST_NEN0(addr1, addr2) int test_neN0_##addr1##_##addr2(void) { return (addr1 char*)NULL != (addr2 char*)0; }
+#define TEST_NENN(addr1, addr2) int test_neNN_##addr1##_##addr2(void) { return (addr1 char*)0 != (addr2 char*)NULL; }
+#define TEST(addr1, addr2) \
+        TEST_EQ00(addr1, addr2) \
+        TEST_EQ0N(addr1, addr2) \
+        TEST_EQN0(addr1, addr2) \
+        TEST_EQNN(addr1, addr2) \
+        TEST_NE00(addr1, addr2) \
+        TEST_NE0N(addr1, addr2) \
+        TEST_NEN0(addr1, addr2) \
+        TEST_NENN(addr1, addr2)
+
+// CHECK-LABEL: test_eq00_generic_private
+// CHECK: ret i32 1
+// CHECK-LABEL: test_eq0N_generic_private
+// CHECK: ret i32 1
+// CHECK-LABEL: test_eqN0_generic_private
+// CHECK: ret i32 1
+// CHECK-LABEL: test_eqNN_generic_private
+// CHECK: ret i32 1
+// CHECK-LABEL: test_ne00_generic_private
+// CHECK: ret i32 0
+// CHECK-LABEL: test_ne0N_generic_private
+// CHECK: ret i32 0
+// CHECK-LABEL: test_neN0_generic_private
+// CHECK: ret i32 0
+// CHECK-LABEL: test_neNN_generic_private
+// CHECK: ret i32 0
+TEST(generic, private)
+
+// CHECK-LABEL: test_eq00_generic_local
+// CHECK: ret i32 1
+// CHECK-LABEL: test_eq0N_generic_local
+// CHECK: ret i32 1
+// CHECK-LABEL: test_eqN0_generic_local
+// CHECK: ret i32 1
+// CHECK-LABEL: test_eqNN_generic_local
+// CHECK: ret i32 1
+// CHECK-LABEL: test_ne00_generic_local
+// CHECK: ret i32 0
+// CHECK-LABEL: test_ne0N_generic_local
+// CHECK: ret i32 0
+// CHECK-LABEL: test_neN0_generic_local
+// CHECK: ret i32 0
+// CHECK-LABEL: test_neNN_generic_local
+// CHECK: ret i32 0
+TEST(generic, local)
+
+// CHECK-LABEL: test_eq00_generic_global
+// CHECK: ret i32 1
+// CHECK-LABEL: test_eq0N_generic_global
+// CHECK: ret i32 1
+// CHECK-LABEL: test_eqN0_generic_global
+// CHECK: ret i32 1
+// CHECK-LABEL: test_eqNN_generic_global
+// CHECK: ret i32 1
+// CHECK-LABEL: test_ne00_generic_global
+// CHECK: ret i32 0
+// CHECK-LABEL: test_ne0N_generic_global
+// CHECK: ret i32 0
+// CHECK-LABEL: test_neN0_generic_global
+// CHECK: ret i32 0
+// CHECK-LABEL: test_neNN_generic_global
+// CHECK: ret i32 0
+TEST(generic, global)
+
+// CHECK-LABEL: test_eq00_generic_generic
+// CHECK: ret i32 1
+// CHECK-LABEL: test_eq0N_generic_generic
+// CHECK: ret i32 1
+// CHECK-LABEL: test_eqN0_generic_generic
+// CHECK: ret i32 1
+// CHECK-LABEL: test_eqNN_generic_generic
+// CHECK: ret i32 1
+// CHECK-LABEL: test_ne00_generic_generic
+// CHECK: ret i32 0
+// CHECK-LABEL: test_ne0N_generic_generic
+// CHECK: ret i32 0
+// CHECK-LABEL: test_neN0_generic_generic
+// CHECK: ret i32 0
+// CHECK-LABEL: test_neNN_generic_generic
+// CHECK: ret i32 0
+TEST(generic, generic)
+
+// CHECK-LABEL: test_eq00_constant_constant
+// CHECK: ret i32 1
+TEST_EQ00(constant, constant)
+
+// Test cast to bool.
+
+// CHECK-LABEL: cast_bool_private
+// CHECK: icmp eq i8* %p, addrspacecast (i8 addrspace(4)* null to i8*)
+void cast_bool_private(private char* p) {
+  if (p)
+    *p = 0;
+}
+
+// CHECK-LABEL: cast_bool_local
+// CHECK: icmp eq i8 addrspace(3)* %p, addrspacecast (i8 addrspace(4)* null to i8 addrspace(3)*)
+void cast_bool_local(local char* p) {
+  if (p)
+    *p = 0;
+}
+
+// CHECK-LABEL: cast_bool_global
+// CHECK: icmp eq i8 addrspace(1)* %p, null
+void cast_bool_global(global char* p) {
+  if (p)
+    *p = 0;
+}
+
+// CHECK-LABEL: cast_bool_constant
+// CHECK: icmp eq i8 addrspace(2)* %p, null
+char cast_bool_constant(constant char* p) {
+  if (p)
+    return *p;
+  else
+    return 0;
+}
+
+// CHECK-LABEL: cast_bool_generic
+// CHECK: icmp eq i8 addrspace(4)* %p, null
+void cast_bool_generic(generic char* p) {
+  if (p)
+    *p = 0;
+}
+
+// Test initialize a struct using memset.
+// For large structures which is mostly zero, clang generats llvm.memset for
+// the zero part and store for non-zero members.
+typedef struct {
+  long a, b, c, d;
+  private char *p;
+} StructTy3;
+
+// CHECK-LABEL: test_memset
+// CHECK: call void @llvm.memset.p0i8.i64(i8* {{.*}}, i8 0, i64 32, i32 8, i1 false)
+// CHECK: store i8* addrspacecast (i8 addrspace(4)* null to i8*), i8** {{.*}}
+StructTy3 test_memset(void) {
+  StructTy3 S3 = {0, 0, 0, 0, 0};
+  return S3;
+}
+
+// Test casting literal 0 to pointer.
+// A 0 literal casted to pointer should become a null pointer.
+
+// CHECK-LABEL: test_cast_0_to_ptr
+// CHECK: ret i32* addrspacecast (i32 addrspace(4)* null to i32*)
+private int* test_cast_0_to_ptr(void) {
+  return (private int*)0;
+}
+
+// Test casting non-literal integer with 0 value to pointer.
+// A non-literal integer expression with 0 value is casted to a pointer with
+// zero value. 
+
+// CHECK-LABEL: test_cast_int_to_ptr1
+// CHECK: ret i32* null
+private int* test_cast_int_to_ptr1(void) {
+  return (private int*)((void)0, 0);
+}
+
+// CHECK-LABEL: test_cast_int_to_ptr2
+// CHECK: ret i32* null
+private int* test_cast_int_to_ptr2(void) {
+  int x = 0;
+  return (private int*)x;
+}
+
+// Test logical operations.
+// CHECK-LABEL: test_not_nullptr
+// CHECK: ret i32 1
+int test_not_nullptr(void) {
+  return !(private char*)NULL;
+}
+
+// CHECK-LABEL: test_and_nullptr
+// CHECK: ret i32 0
+int test_and_nullptr(int a) {
+  return a && ((private char*)NULL);
+}
+
+// CHECK-LABEL: test_not_ptr
+// CHECK: %[[lnot:.*]] = icmp eq i8* %p, addrspacecast (i8 addrspace(4)* null to i8*)
+// CHECK: %[[lnot_ext:.*]] = zext i1 %[[lnot]] to i32
+// CHECK: ret i32 %[[lnot_ext]]
+int test_not_ptr(private char* p) {
+  return !p;
+}
+// CHECK-LABEL: test_and_ptr
+// CHECK: %[[tobool:.*]] = icmp ne i8* %p1, addrspacecast (i8 addrspace(4)* null to i8*)
+// CHECK: %[[tobool1:.*]] = icmp ne i8 addrspace(3)* %p2, addrspacecast (i8 addrspace(4)* null to i8 addrspace(3)*)
+// CHECK: %[[res:.*]] = and i1 %[[tobool]], %[[tobool1]]
+// CHECK: %[[land_ext:.*]] = zext i1 %[[res]] to i32
+// CHECK: ret i32 %[[land_ext]]
+int test_and_ptr(private char* p1, local char* p2) {
+  return p1 && p2;
+}
+
+// Test folding of null pointer in function scope.
+// NOOPT-LABEL: test_fold
+// NOOPT: call void @test_fold_callee
+// NOOPT: store i32 addrspace(1)* null, i32 addrspace(1)** %glob, align 4
+// NOOPT: %{{.*}} = sub i64 %{{.*}}, 0
+// NOOPT: call void @test_fold_callee
+// NOOPT: %{{.*}} = add nsw i64 %{{.*}}, sext (i32 ptrtoint (i32* addrspacecast (i32 addrspace(4)* null to i32*) to i32) to i64)
+// NOOPT: %{{.*}} = sub nsw i64 %{{.*}}, 1
+void test_fold_callee(void);
+void test_fold(void) {
+  global int* glob = (test_fold_callee(), (global int*)(generic char*)0);
+  long x = glob - (global int*)(generic char*)0;
+  x = x + (int)(test_fold_callee(), (private int*)(generic char*)(global short*)0);
+  x = x - (int)((private int*)0 == (private int*)(generic char*)0);
+}