[flang] Further work on NULL(MOLD=allocatable) (#129345)

Refine handling of NULL(...) in semantics to properly distinguish
NULL(), NULL(objectPointer), NULL(procPointer), and NULL(allocatable)
from each other in relevant contexts.

Add IsNullAllocatable() and IsNullPointerOrAllocatable() utility
functions. IsNullAllocatable() is true only for NULL(allocatable); it is
false for a bare NULL(), which can be detected independently with
IsBareNullPointer().

IsNullPointer() now returns false for NULL(allocatable).

ALLOCATED(NULL(allocatable)) now works, and folds to .FALSE.

These utilities were modified to accept const pointer arguments rather
than const references; I usually prefer this style when the result
should clearly be false for a null argument (in the C sense), and it
helped me find all of their use sites in the code.

flang/include/flang/Evaluate/characteristics.h

@@ -349,8 +349,8 @@ struct FunctionResult {
 
 // 15.3.1
 struct Procedure {
-  ENUM_CLASS(
+  ENUM_CLASS(Attr, Pure, Elemental, BindC, ImplicitInterface, NullPointer,
-      Attr, Pure, Elemental, BindC, ImplicitInterface, NullPointer, Subroutine)
+      NullAllocatable, Subroutine)
   using Attrs = common::EnumSet<Attr, Attr_enumSize>;
   Procedure(){};
   Procedure(FunctionResult &&, DummyArguments &&, Attrs);

flang/include/flang/Evaluate/tools.h

@@ -1059,9 +1059,11 @@ bool IsProcedurePointer(const Expr<SomeType> &);
 bool IsProcedure(const Expr<SomeType> &);
 bool IsProcedurePointerTarget(const Expr<SomeType> &);
 bool IsBareNullPointer(const Expr<SomeType> *); // NULL() w/o MOLD= or type
-bool IsNullObjectPointer(const Expr<SomeType> &);
+bool IsNullObjectPointer(const Expr<SomeType> *); // NULL() or NULL(objptr)
-bool IsNullProcedurePointer(const Expr<SomeType> &);
+bool IsNullProcedurePointer(const Expr<SomeType> *); // NULL() or NULL(procptr)
-bool IsNullPointer(const Expr<SomeType> &);
+bool IsNullPointer(const Expr<SomeType> *); // NULL() or NULL(pointer)
+bool IsNullAllocatable(const Expr<SomeType> *); // NULL(allocatable)
+bool IsNullPointerOrAllocatable(const Expr<SomeType> *); // NULL of any form
 bool IsObjectPointer(const Expr<SomeType> &);
 
 // Can Expr be passed as absent to an optional dummy argument.

flang/lib/Evaluate/check-expression.cpp

@@ -100,9 +100,9 @@ template <bool INVARIANT>
 bool IsConstantExprHelper<INVARIANT>::IsConstantStructureConstructorComponent(
     const Symbol &component, const Expr<SomeType> &expr) const {
   if (IsAllocatable(component)) {
-    return IsNullObjectPointer(expr);
+    return IsNullObjectPointer(&expr);
   } else if (IsPointer(component)) {
-    return IsNullPointer(expr) || IsInitialDataTarget(expr) ||
+    return IsNullPointerOrAllocatable(&expr) || IsInitialDataTarget(expr) ||
         IsInitialProcedureTarget(expr);
   } else {
     return (*this)(expr);
@@ -194,7 +194,7 @@ struct IsActuallyConstantHelper {
       const bool compIsConstant{(*this)(y)};
       // If an allocatable component is initialized by a constant,
       // the structure constructor is not a constant.
-      if ((!compIsConstant && !IsNullPointer(y)) ||
+      if ((!compIsConstant && !IsNullPointerOrAllocatable(&y)) ||
           (compIsConstant && IsAllocatable(sym))) {
         return false;
       }
@@ -311,7 +311,9 @@ public:
   bool operator()(const ProcedureRef &x) const {
     if (const SpecificIntrinsic * intrinsic{x.proc().GetSpecificIntrinsic()}) {
       return intrinsic->characteristics.value().attrs.test(
-          characteristics::Procedure::Attr::NullPointer);
+                 characteristics::Procedure::Attr::NullPointer) ||
+          intrinsic->characteristics.value().attrs.test(
+              characteristics::Procedure::Attr::NullAllocatable);
     }
     return false;
   }
@@ -388,7 +390,7 @@ bool IsInitialProcedureTarget(const Expr<SomeType> &expr) {
   if (const auto *proc{std::get_if<ProcedureDesignator>(&expr.u)}) {
     return IsInitialProcedureTarget(*proc);
   } else {
-    return IsNullProcedurePointer(expr);
+    return IsNullProcedurePointer(&expr);
   }
 }
 

flang/lib/Evaluate/fold-logical.cpp

@@ -652,21 +652,18 @@ Expr<Type<TypeCategory::Logical, KIND>> FoldIntrinsicFunction(
   if (name == "all") {
     return FoldAllAnyParity(
         context, std::move(funcRef), &Scalar<T>::AND, Scalar<T>{true});
+  } else if (name == "allocated") {
+    if (IsNullAllocatable(args[0]->UnwrapExpr())) {
+      return Expr<T>{false};
+    }
   } else if (name == "any") {
     return FoldAllAnyParity(
         context, std::move(funcRef), &Scalar<T>::OR, Scalar<T>{false});
   } else if (name == "associated") {
-    bool gotConstant{true};
+    if (IsNullPointer(args[0]->UnwrapExpr()) ||
-    const Expr<SomeType> *firstArgExpr{args[0]->UnwrapExpr()};
+        (args[1] && IsNullPointer(args[1]->UnwrapExpr()))) {
-    if (!firstArgExpr || !IsNullPointer(*firstArgExpr)) {
+      return Expr<T>{false};
-      gotConstant = false;
-    } else if (args[1]) { // There's a second argument
-      const Expr<SomeType> *secondArgExpr{args[1]->UnwrapExpr()};
-      if (!secondArgExpr || !IsNullPointer(*secondArgExpr)) {
-        gotConstant = false;
-      }
     }
-    return gotConstant ? Expr<T>{false} : Expr<T>{std::move(funcRef)};
   } else if (name == "bge" || name == "bgt" || name == "ble" || name == "blt") {
     static_assert(std::is_same_v<Scalar<LargestInt>, BOZLiteralConstant>);
 

flang/lib/Evaluate/fold.cpp

@@ -73,7 +73,7 @@ Expr<SomeDerived> FoldOperation(
   for (auto &&[symbol, value] : std::move(structure)) {
     auto expr{Fold(context, std::move(value.value()))};
     if (IsPointer(symbol)) {
-      if (IsNullPointer(expr)) {
+      if (IsNullPointer(&expr)) {
         // Handle x%c when x designates a named constant of derived
         // type and %c is NULL() in that constant.
         expr = Expr<SomeType>{NullPointer{}};
@@ -86,9 +86,10 @@ Expr<SomeDerived> FoldOperation(
       // F2023: 10.1.12 (3)(a)
       // If comp-spec is not null() for the allocatable component the
       // structure constructor is not a constant expression.
-      isConstant &= IsNullPointer(expr);
+      isConstant &= IsNullAllocatable(&expr) || IsBareNullPointer(&expr);
     } else {
-      isConstant &= IsActuallyConstant(expr) || IsNullPointer(expr);
+      isConstant &=
+          IsActuallyConstant(expr) || IsNullPointerOrAllocatable(&expr);
       if (auto valueShape{GetConstantExtents(context, expr)}) {
         if (auto componentShape{GetConstantExtents(context, symbol)}) {
           if (GetRank(*componentShape) > 0 && GetRank(*valueShape) == 0) {

flang/lib/Evaluate/intrinsics.cpp

@@ -247,8 +247,10 @@ ENUM_CLASS(Optionality, required,
 )
 
 ENUM_CLASS(ArgFlag, none,
-    canBeNull, // actual argument can be NULL(with or without MOLD=)
+    canBeNullPointer, // actual argument can be NULL(with or without
-    canBeMoldNull, // actual argument can be NULL(with MOLD=)
+                      // MOLD=pointer)
+    canBeMoldNull, // actual argument can be NULL(MOLD=any)
+    canBeNullAllocatable, // actual argument can be NULL(MOLD=allocatable)
     defaultsToSameKind, // for MatchingDefaultKIND
     defaultsToSizeKind, // for SizeDefaultKIND
     defaultsToDefaultForResult, // for DefaultingKIND
@@ -343,8 +345,10 @@ static const IntrinsicInterface genericIntrinsicFunction[]{
         Rank::dimReduced, IntrinsicClass::transformationalFunction},
     {"allocated", {{"scalar", AnyData, Rank::scalar}}, DefaultLogical,
         Rank::elemental, IntrinsicClass::inquiryFunction},
-    {"allocated", {{"array", AnyData, Rank::anyOrAssumedRank}}, DefaultLogical,
+    {"allocated",
-        Rank::elemental, IntrinsicClass::inquiryFunction},
+        {{"array", AnyData, Rank::anyOrAssumedRank, Optionality::required,
+            common::Intent::In, {ArgFlag::canBeNullAllocatable}}},
+        DefaultLogical, Rank::elemental, IntrinsicClass::inquiryFunction},
     {"anint", {{"a", SameReal}, MatchingDefaultKIND}, KINDReal},
     {"any", {{"mask", SameLogical, Rank::array}, OptionalDIM}, SameLogical,
         Rank::dimReduced, IntrinsicClass::transformationalFunction},
@@ -353,10 +357,10 @@ static const IntrinsicInterface genericIntrinsicFunction[]{
     {"asinh", {{"x", SameFloating}}, SameFloating},
     {"associated",
         {{"pointer", AnyPointer, Rank::anyOrAssumedRank, Optionality::required,
-             common::Intent::In, {ArgFlag::canBeNull}},
+             common::Intent::In, {ArgFlag::canBeNullPointer}},
             {"target", Addressable, Rank::anyOrAssumedRank,
                 Optionality::optional, common::Intent::In,
-                {ArgFlag::canBeNull}}},
+                {ArgFlag::canBeNullPointer}}},
         DefaultLogical, Rank::elemental, IntrinsicClass::inquiryFunction},
     {"atan", {{"x", SameFloating}}, SameFloating},
     {"atan", {{"y", OperandReal}, {"x", OperandReal}}, OperandReal},
@@ -1892,9 +1896,9 @@ std::optional<SpecificCall> IntrinsicInterface::Match(
           d.keyword);
       return std::nullopt;
     }
-    if (!d.flags.test(ArgFlag::canBeNull)) {
+    if (!d.flags.test(ArgFlag::canBeNullPointer)) {
-      if (const auto *expr{arg->UnwrapExpr()}; expr && IsNullPointer(*expr)) {
+      if (const auto *expr{arg->UnwrapExpr()}; IsNullPointer(expr)) {
-        if (!IsBareNullPointer(expr) && IsNullObjectPointer(*expr) &&
+        if (!IsBareNullPointer(expr) && IsNullObjectPointer(expr) &&
             d.flags.test(ArgFlag::canBeMoldNull)) {
           // ok
         } else {
@@ -1905,6 +1909,14 @@ std::optional<SpecificCall> IntrinsicInterface::Match(
         }
       }
     }
+    if (!d.flags.test(ArgFlag::canBeNullAllocatable) &&
+        IsNullAllocatable(arg->UnwrapExpr()) &&
+        !d.flags.test(ArgFlag::canBeMoldNull)) {
+      messages.Say(arg->sourceLocation(),
+          "A NULL() allocatable is not allowed for '%s=' intrinsic argument"_err_en_US,
+          d.keyword);
+      return std::nullopt;
+    }
     if (d.flags.test(ArgFlag::notAssumedSize)) {
       if (auto named{ExtractNamedEntity(*arg)}) {
         if (semantics::IsAssumedSizeArray(named->GetLastSymbol())) {
@@ -2862,14 +2874,15 @@ SpecificCall IntrinsicProcTable::Implementation::HandleNull(
             "MOLD= argument to NULL() must not be assumed-rank"_err_en_US);
       }
       bool isProcPtrTarget{
-          IsProcedurePointerTarget(*mold) && !IsNullObjectPointer(*mold)};
+          IsProcedurePointerTarget(*mold) && !IsNullObjectPointer(mold)};
       if (isProcPtrTarget || IsAllocatableOrPointerObject(*mold)) {
         characteristics::DummyArguments args;
         std::optional<characteristics::FunctionResult> fResult;
+        bool isAllocatableMold{false};
         if (isProcPtrTarget) {
           // MOLD= procedure pointer
           std::optional<characteristics::Procedure> procPointer;
-          if (IsNullProcedurePointer(*mold)) {
+          if (IsNullProcedurePointer(mold)) {
             procPointer =
                 characteristics::Procedure::Characterize(*mold, context);
           } else {
@@ -2885,12 +2898,13 @@ SpecificCall IntrinsicProcTable::Implementation::HandleNull(
             fResult.emplace(std::move(*procPointer));
           }
         } else if (auto type{mold->GetType()}) {
-          // MOLD= object pointer
+          // MOLD= object pointer or allocatable
           characteristics::TypeAndShape typeAndShape{
               *type, GetShape(context, *mold)};
           args.emplace_back(
               "mold"s, characteristics::DummyDataObject{typeAndShape});
           fResult.emplace(std::move(typeAndShape));
+          isAllocatableMold = IsAllocatableDesignator(*mold);
         } else {
           context.messages().Say(arguments[0]->sourceLocation(),
               "MOLD= argument to NULL() lacks type"_err_en_US);
@@ -2898,7 +2912,9 @@ SpecificCall IntrinsicProcTable::Implementation::HandleNull(
         if (fResult) {
           fResult->attrs.set(characteristics::FunctionResult::Attr::Pointer);
           characteristics::Procedure::Attrs attrs;
-          attrs.set(characteristics::Procedure::Attr::NullPointer);
+          attrs.set(isAllocatableMold
+                  ? characteristics::Procedure::Attr::NullAllocatable
+                  : characteristics::Procedure::Attr::NullPointer);
           characteristics::Procedure chars{
               std::move(*fResult), std::move(args), attrs};
           return SpecificCall{SpecificIntrinsic{"null"s, std::move(chars)},
@@ -3257,7 +3273,7 @@ static bool ApplySpecificChecks(SpecificCall &call, FoldingContext &context) {
     const auto &arg{call.arguments[0]};
     if (arg) {
       if (const auto *expr{arg->UnwrapExpr()}) {
-        ok = evaluate::IsAllocatableDesignator(*expr);
+        ok = IsAllocatableDesignator(*expr) || IsNullAllocatable(expr);
       }
     }
     if (!ok) {

flang/lib/Evaluate/shape.cpp

@@ -1173,8 +1173,10 @@ auto GetShapeHelper::operator()(const ProcedureRef &call) const -> Result {
       if (call.arguments().size() >= 2) {
         return (*this)(call.arguments()[1]); // MASK=
       }
-    } else if (intrinsic->characteristics.value().attrs.test(characteristics::
+    } else if (intrinsic->characteristics.value().attrs.test(
-                       Procedure::Attr::NullPointer)) { // NULL(MOLD=)
+                   characteristics::Procedure::Attr::NullPointer) ||
+        intrinsic->characteristics.value().attrs.test(
+            characteristics::Procedure::Attr::NullAllocatable)) { // NULL(MOLD=)
       return (*this)(call.arguments());
     } else {
       // TODO: shapes of other non-elemental intrinsic results

flang/lib/Evaluate/tools.cpp

@@ -929,7 +929,7 @@ bool IsPointer(const Expr<SomeType> &expr) {
 }
 
 bool IsProcedurePointer(const Expr<SomeType> &expr) {
-  if (IsNullProcedurePointer(expr)) {
+  if (IsNullProcedurePointer(&expr)) {
     return true;
   } else if (const auto *funcRef{UnwrapProcedureRef(expr)}) {
     if (const Symbol * proc{funcRef->proc().GetSymbol()}) {
@@ -963,7 +963,7 @@ bool IsProcedurePointerTarget(const Expr<SomeType> &expr) {
 }
 
 bool IsObjectPointer(const Expr<SomeType> &expr) {
-  if (IsNullObjectPointer(expr)) {
+  if (IsNullObjectPointer(&expr)) {
     return true;
   } else if (IsProcedurePointerTarget(expr)) {
     return false;
@@ -1030,15 +1030,15 @@ template <bool IS_PROC_PTR> struct IsNullPointerHelper {
   }
 };
 
-bool IsNullObjectPointer(const Expr<SomeType> &expr) {
+bool IsNullObjectPointer(const Expr<SomeType> *expr) {
-  return IsNullPointerHelper<false>{}(expr);
+  return expr && IsNullPointerHelper<false>{}(*expr);
 }
 
-bool IsNullProcedurePointer(const Expr<SomeType> &expr) {
+bool IsNullProcedurePointer(const Expr<SomeType> *expr) {
-  return IsNullPointerHelper<true>{}(expr);
+  return expr && IsNullPointerHelper<true>{}(*expr);
 }
 
-bool IsNullPointer(const Expr<SomeType> &expr) {
+bool IsNullPointer(const Expr<SomeType> *expr) {
   return IsNullObjectPointer(expr) || IsNullProcedurePointer(expr);
 }
 
@@ -1046,6 +1046,30 @@ bool IsBareNullPointer(const Expr<SomeType> *expr) {
   return expr && std::holds_alternative<NullPointer>(expr->u);
 }
 
+struct IsNullAllocatableHelper {
+  template <typename A> bool operator()(const A &) const { return false; }
+  template <typename T> bool operator()(const FunctionRef<T> &call) const {
+    const auto *intrinsic{call.proc().GetSpecificIntrinsic()};
+    return intrinsic &&
+        intrinsic->characteristics.value().attrs.test(
+            characteristics::Procedure::Attr::NullAllocatable);
+  }
+  template <typename T> bool operator()(const Parentheses<T> &x) const {
+    return (*this)(x.left());
+  }
+  template <typename T> bool operator()(const Expr<T> &x) const {
+    return common::visit(*this, x.u);
+  }
+};
+
+bool IsNullAllocatable(const Expr<SomeType> *x) {
+  return x && IsNullAllocatableHelper{}(*x);
+}
+
+bool IsNullPointerOrAllocatable(const Expr<SomeType> *x) {
+  return IsNullPointer(x) || IsNullAllocatable(x);
+}
+
 // GetSymbolVector()
 auto GetSymbolVectorHelper::operator()(const Symbol &x) const -> Result {
   if (const auto *details{x.detailsIf<semantics::AssocEntityDetails>()}) {
@@ -1393,7 +1417,7 @@ bool IsAllocatableOrPointerObject(const Expr<SomeType> &expr) {
   const semantics::Symbol *sym{UnwrapWholeSymbolOrComponentDataRef(expr)};
   return (sym &&
              semantics::IsAllocatableOrObjectPointer(&sym->GetUltimate())) ||
-      evaluate::IsObjectPointer(expr);
+      evaluate::IsObjectPointer(expr) || evaluate::IsNullAllocatable(&expr);
 }
 
 bool IsAllocatableDesignator(const Expr<SomeType> &expr) {

flang/lib/Lower/ConvertConstant.cpp

@@ -370,7 +370,7 @@ static mlir::Value genStructureComponentInit(
       /*typeParams=*/mlir::ValueRange{} /*TODO*/);
 
   if (Fortran::semantics::IsAllocatable(sym)) {
-    if (!Fortran::evaluate::IsNullPointer(expr)) {
+    if (!Fortran::evaluate::IsNullPointerOrAllocatable(&expr)) {
       fir::emitFatalError(loc, "constant structure constructor with an "
                                "allocatable component value that is not NULL");
     } else {
@@ -414,7 +414,7 @@ static mlir::Value genStructureComponentInit(
   // must fall through to genConstantValue() below.
   if (Fortran::semantics::IsBuiltinCPtr(sym) && sym.Rank() == 0 &&
       (Fortran::evaluate::GetLastSymbol(expr) ||
-       Fortran::evaluate::IsNullPointer(expr))) {
+       Fortran::evaluate::IsNullPointer(&expr))) {
     // Builtin c_ptr and c_funptr have special handling because designators
     // and NULL() are handled as initial values for them as an extension
     // (otherwise only c_ptr_null/c_funptr_null are allowed and these are

flang/lib/Semantics/check-call.cpp

@@ -62,7 +62,7 @@ static void CheckImplicitInterfaceArg(evaluate::ActualArgument &arg,
     }
     if (IsBOZLiteral(*expr)) {
       messages.Say("BOZ argument requires an explicit interface"_err_en_US);
-    } else if (evaluate::IsNullPointer(*expr)) {
+    } else if (evaluate::IsNullPointerOrAllocatable(expr)) {
       messages.Say(
           "Null pointer argument requires an explicit interface"_err_en_US);
     } else if (auto named{evaluate::ExtractNamedEntity(*expr)}) {
@@ -783,7 +783,6 @@ static void CheckExplicitDataArg(const characteristics::DummyDataObject &dummy,
   // 15.5.2.6 -- dummy is ALLOCATABLE
   bool dummyIsOptional{
       dummy.attrs.test(characteristics::DummyDataObject::Attr::Optional)};
-  bool actualIsNull{evaluate::IsNullPointer(actual)};
   if (dummyIsAllocatable) {
     if (actualIsAllocatable) {
       if (actualIsCoindexed && dummy.intent != common::Intent::In) {
@@ -791,7 +790,7 @@ static void CheckExplicitDataArg(const characteristics::DummyDataObject &dummy,
             "ALLOCATABLE %s must have INTENT(IN) to be associated with a coindexed actual argument"_err_en_US,
             dummyName);
       }
-    } else if (actualIsNull) {
+    } else if (evaluate::IsBareNullPointer(&actual)) {
       if (dummyIsOptional) {
       } else if (dummy.intent == common::Intent::Default &&
           context.ShouldWarn(
@@ -808,6 +807,16 @@ static void CheckExplicitDataArg(const characteristics::DummyDataObject &dummy,
       }
       // INTENT(OUT) and INTENT(IN OUT) cases are caught elsewhere as being
       // undefinable actual arguments.
+    } else if (evaluate::IsNullAllocatable(&actual)) {
+      if (dummyIsOptional) {
+      } else if (dummy.intent == common::Intent::Default &&
+          context.ShouldWarn(
+              common::UsageWarning::NullActualForDefaultIntentAllocatable)) {
+        messages.Say(
+            "A null allocatable should not be associated with allocatable %s without INTENT(IN)"_warn_en_US,
+            dummyName);
+      }
+      // INTENT(OUT) and INTENT(IN OUT) cases are caught elsewhere
     } else {
       messages.Say(
           "ALLOCATABLE %s must be associated with an ALLOCATABLE actual argument"_err_en_US,
@@ -946,7 +955,7 @@ static void CheckExplicitDataArg(const characteristics::DummyDataObject &dummy,
 
   // NULL(MOLD=) checking for non-intrinsic procedures
   if (!intrinsic && !dummyIsAllocatableOrPointer && !dummyIsOptional &&
-      actualIsNull) {
+      evaluate::IsNullPointer(&actual)) {
     messages.Say(
         "Actual argument associated with %s may not be null pointer %s"_err_en_US,
         dummyName, actual.AsFortran());
@@ -1091,6 +1100,8 @@ static void CheckProcedureArg(evaluate::ActualArgument &arg,
           characteristics::Procedure &argInterface{argProc->procedure.value()};
           argInterface.attrs.reset(
               characteristics::Procedure::Attr::NullPointer);
+          argInterface.attrs.reset(
+              characteristics::Procedure::Attr::NullAllocatable);
           if (!argProcSymbol || argProcSymbol->attrs().test(Attr::INTRINSIC)) {
             // It's ok to pass ELEMENTAL unrestricted intrinsic functions.
             argInterface.attrs.reset(
@@ -1105,6 +1116,8 @@ static void CheckProcedureArg(evaluate::ActualArgument &arg,
             } else {
               argInterface.attrs.reset(
                   characteristics::Procedure::Attr::NullPointer);
+              argInterface.attrs.reset(
+                  characteristics::Procedure::Attr::NullAllocatable);
             }
           }
           if (interface.HasExplicitInterface()) {
@@ -1161,7 +1174,7 @@ static void CheckProcedureArg(evaluate::ActualArgument &arg,
               "Actual argument associated with procedure %s is not a procedure"_err_en_US,
               dummyName);
         }
-      } else if (IsNullPointer(*expr)) {
+      } else if (IsNullPointer(expr)) {
         if (!dummyIsPointer &&
             !dummy.attrs.test(
                 characteristics::DummyProcedure::Attr::Optional)) {
@@ -1263,11 +1276,11 @@ static void CheckExplicitInterfaceArg(evaluate::ActualArgument &arg,
                     IsBOZLiteral(*expr)) {
                   // ok
                 } else if (object.type.type().IsTypelessIntrinsicArgument() &&
-                    evaluate::IsNullObjectPointer(*expr)) {
+                    evaluate::IsNullObjectPointer(expr)) {
                   // ok, ASSOCIATED(NULL(without MOLD=))
                 } else if (object.type.attrs().test(characteristics::
                                    TypeAndShape::Attr::AssumedRank) &&
-                    evaluate::IsNullObjectPointer(*expr) &&
+                    evaluate::IsNullObjectPointer(expr) &&
                     (object.attrs.test(
                          characteristics::DummyDataObject::Attr::Allocatable) ||
                         object.attrs.test(
@@ -1280,7 +1293,7 @@ static void CheckExplicitInterfaceArg(evaluate::ActualArgument &arg,
                                     Attr::Pointer) ||
                                object.attrs.test(characteristics::
                                        DummyDataObject::Attr::Optional)) &&
-                    evaluate::IsNullObjectPointer(*expr)) {
+                    evaluate::IsNullObjectPointer(expr)) {
                   // FOO(NULL(without MOLD=))
                   if (object.type.type().IsAssumedLengthCharacter()) {
                     messages.Say(
@@ -1299,7 +1312,8 @@ static void CheckExplicitInterfaceArg(evaluate::ActualArgument &arg,
                   }
                 } else if (object.attrs.test(characteristics::DummyDataObject::
                                    Attr::Allocatable) &&
-                    evaluate::IsNullPointer(*expr)) {
+                    (evaluate::IsNullAllocatable(expr) ||
+                        evaluate::IsBareNullPointer(expr))) {
                   if (object.intent == common::Intent::Out ||
                       object.intent == common::Intent::InOut) {
                     messages.Say(
@@ -1573,13 +1587,13 @@ static void CheckAssociated(evaluate::ActualArguments &arguments,
                     }
                   }
                 }
-              } else if (!IsNullProcedurePointer(*targetExpr)) {
+              } else if (!IsNullProcedurePointer(targetExpr)) {
                 messages.Say(
                     "POINTER= argument '%s' is a procedure pointer but the TARGET= argument '%s' is not a procedure or procedure pointer"_err_en_US,
                     pointerExpr->AsFortran(), targetExpr->AsFortran());
               }
             }
-          } else if (IsVariable(*targetExpr) || IsNullPointer(*targetExpr)) {
+          } else if (IsVariable(*targetExpr) || IsNullPointer(targetExpr)) {
             // Object pointer and target
             if (ExtractDataRef(*targetExpr)) {
               if (SymbolVector symbols{GetSymbolVector(*targetExpr)};

flang/lib/Semantics/data-to-inits.cpp

@@ -381,7 +381,7 @@ bool DataInitializationCompiler<DSV>::InitElement(
     if (static_cast<std::size_t>(offsetSymbol.offset() + offsetSymbol.size()) >
         symbol.size()) {
       OutOfRangeError();
-    } else if (evaluate::IsNullPointer(*expr)) {
+    } else if (evaluate::IsNullPointer(expr)) {
       // nothing to do; rely on zero initialization
       return true;
     } else if (isProcPointer) {
@@ -414,7 +414,7 @@ bool DataInitializationCompiler<DSV>::InitElement(
       GetImage().AddPointer(offsetSymbol.offset(), *expr);
       return true;
     }
-  } else if (evaluate::IsNullPointer(*expr)) {
+  } else if (evaluate::IsNullPointer(expr)) {
     exprAnalyzer_.Say("Initializer for '%s' must not be a pointer"_err_en_US,
         DescribeElement());
   } else if (evaluate::IsProcedureDesignator(*expr)) {
@@ -900,7 +900,7 @@ void ConstructInitializer(const Symbol &symbol,
           mutableProc.set_init(DEREF(procDesignator->GetSymbol()));
         }
       } else {
-        CHECK(evaluate::IsNullProcedurePointer(*expr));
+        CHECK(evaluate::IsNullProcedurePointer(&*expr));
         mutableProc.set_init(nullptr);
       }
     } else {

flang/lib/Semantics/definable.cpp

@@ -381,7 +381,7 @@ std::optional<parser::Message> WhyNotDefinable(parser::CharBlock at,
     if (auto whyNotDataRef{WhyNotDefinable(at, scope, flags, *dataRef)}) {
       return whyNotDataRef;
     }
-  } else if (evaluate::IsNullPointer(expr)) {
+  } else if (evaluate::IsNullPointerOrAllocatable(&expr)) {
     return parser::Message{
         at, "'%s' is a null pointer"_err_en_US, expr.AsFortran()};
   } else if (flags.test(DefinabilityFlag::PointerDefinition)) {

flang/lib/Semantics/expression.cpp

@@ -2167,7 +2167,7 @@ MaybeExpr ExpressionAnalyzer::Analyze(
           result.Add(*symbol, Fold(std::move(*value)));
           continue;
         }
-        if (IsNullPointer(*value)) {
+        if (IsNullPointer(&*value)) {
           if (IsAllocatable(*symbol)) {
             if (IsBareNullPointer(&*value)) {
               // NULL() with no arguments allowed by 7.5.10 para 6 for
@@ -2175,7 +2175,7 @@ MaybeExpr ExpressionAnalyzer::Analyze(
               result.Add(*symbol, Expr<SomeType>{NullPointer{}});
               continue;
             }
-            if (IsNullObjectPointer(*value)) {
+            if (IsNullObjectPointer(&*value)) {
               AttachDeclaration(
                   Warn(common::LanguageFeature::
                            NullMoldAllocatableComponentValue,
@@ -2200,8 +2200,11 @@ MaybeExpr ExpressionAnalyzer::Analyze(
                 *symbol);
             continue;
           }
+        } else if (IsNullAllocatable(&*value) && IsAllocatable(*symbol)) {
+          result.Add(*symbol, Expr<SomeType>{NullPointer{}});
+          continue;
         } else if (const Symbol * pointer{FindPointerComponent(*symbol)};
-                   pointer && pureContext) { // C1594(4)
+            pointer && pureContext) { // C1594(4)
           if (const Symbol *
               visible{semantics::FindExternallyVisibleObject(
                   *value, *pureContext)}) {
@@ -2522,10 +2525,13 @@ static bool CheckCompatibleArgument(bool isElemental,
   return common::visit(
       common::visitors{
           [&](const characteristics::DummyDataObject &x) {
-            if (x.attrs.test(characteristics::DummyDataObject::Attr::Pointer) &&
+            if ((x.attrs.test(
+                     characteristics::DummyDataObject::Attr::Pointer) ||
+                    x.attrs.test(
+                        characteristics::DummyDataObject::Attr::Allocatable)) &&
                 IsBareNullPointer(expr)) {
               // NULL() without MOLD= is compatible with any dummy data pointer
-              // but cannot be allowed to lead to ambiguity.
+              // or allocatable, but cannot be allowed to lead to ambiguity.
               return true;
             } else if (!isElemental && actual.Rank() != x.type.Rank() &&
                 !x.type.attrs().test(
@@ -3877,7 +3883,7 @@ MaybeExpr ExpressionAnalyzer::ExprOrVariable(
   }
   if (result) {
     if constexpr (std::is_same_v<PARSED, parser::Expr>) {
-      if (!isNullPointerOk_ && IsNullPointer(*result)) {
+      if (!isNullPointerOk_ && IsNullPointerOrAllocatable(&*result)) {
         Say(source,
             "NULL() may not be used as an expression in this context"_err_en_US);
       }
@@ -4396,15 +4402,11 @@ bool ArgumentAnalyzer::CheckAssignmentConformance() {
 
 bool ArgumentAnalyzer::CheckForNullPointer(const char *where) {
   for (const std::optional<ActualArgument> &arg : actuals_) {
-    if (arg) {
+    if (arg && IsNullPointerOrAllocatable(arg->UnwrapExpr())) {
-      if (const Expr<SomeType> *expr{arg->UnwrapExpr()}) {
+      context_.Say(
-        if (IsNullPointer(*expr)) {
+          source_, "A NULL() pointer is not allowed %s"_err_en_US, where);
-          context_.Say(
+      fatalErrors_ = true;
-              source_, "A NULL() pointer is not allowed %s"_err_en_US, where);
+      return false;
-          fatalErrors_ = true;
-          return false;
-        }
-      }
     }
   }
   return true;

flang/lib/Semantics/pointer-assignment.cpp

@@ -184,7 +184,7 @@ bool PointerAssignmentChecker::Check(const SomeExpr &rhs) {
   if (!common::visit([&](const auto &x) { return Check(x); }, rhs.u)) {
     return false;
   }
-  if (IsNullPointer(rhs)) {
+  if (IsNullPointer(&rhs)) {
     return true;
   }
   if (lhs_ && IsProcedure(*lhs_)) {

flang/lib/Semantics/resolve-names.cpp

@@ -6225,7 +6225,8 @@ bool DeclarationVisitor::Pre(const parser::ProcPointerInit &x) {
     const auto &null{DEREF(std::get_if<parser::NullInit>(&x.u))};
     Walk(null);
     if (auto nullInit{EvaluateExpr(null)}) {
-      if (!evaluate::IsNullPointer(*nullInit)) {
+      if (!evaluate::IsNullProcedurePointer(&*nullInit) &&
+          !evaluate::IsBareNullPointer(&*nullInit)) {
         Say(null.v.value().source,
             "Procedure pointer initializer must be a name or intrinsic NULL()"_err_en_US);
       }
@@ -8634,7 +8635,7 @@ void DeclarationVisitor::Initialization(const parser::Name &name,
           [&](const parser::NullInit &null) { // => NULL()
             Walk(null);
             if (auto nullInit{EvaluateExpr(null)}) {
-              if (!evaluate::IsNullPointer(*nullInit)) { // C813
+              if (!evaluate::IsNullPointer(&*nullInit)) { // C813
                 Say(null.v.value().source,
                     "Pointer initializer must be intrinsic NULL()"_err_en_US);
               } else if (IsPointer(ultimate)) {
@@ -8684,7 +8685,7 @@ void DeclarationVisitor::PointerInitialization(
             ultimate.set(Symbol::Flag::InDataStmt, false);
           } else if (auto *details{ultimate.detailsIf<ProcEntityDetails>()}) {
             // something like "REAL, EXTERNAL, POINTER :: p => t"
-            if (evaluate::IsNullProcedurePointer(*expr)) {
+            if (evaluate::IsNullProcedurePointer(&*expr)) {
               CHECK(!details->init());
               details->set_init(nullptr);
             } else if (const Symbol *

flang/test/Evaluate/folding06.f90

@@ -3,7 +3,7 @@
 
 module m
 
-  ! Testing ASSOCATED
+  ! Testing ASSOCIATED and ALLOCATED
   integer, pointer :: int_pointer
   integer, allocatable :: int_allocatable
   logical, parameter :: test_Assoc1 = .not.(associated(null()))
@@ -11,13 +11,10 @@ module m
   !WARN: because: 'NULL()' is a null pointer
   logical, parameter :: test_Assoc2 = .not.(associated(null(), null()))
   logical, parameter :: test_Assoc3 = .not.(associated(null(int_pointer)))
-  logical, parameter :: test_Assoc4 = .not.(associated(null(int_allocatable)))
+  logical, parameter :: test_Alloc1 = .not.(allocated(null(int_allocatable)))
   !WARN: portability: POINTER= argument of ASSOCIATED() is required by some other compilers to be a valid left-hand side of a pointer assignment statement
   !WARN: because: 'NULL()' is a null pointer
-  logical, parameter :: test_Assoc5 = .not.(associated(null(), null(int_pointer)))
+  logical, parameter :: test_Assoc5 = .not. associated(null(), null(int_pointer))
-  !WARN: portability: POINTER= argument of ASSOCIATED() is required by some other compilers to be a valid left-hand side of a pointer assignment statement
-  !WARN: because: 'NULL()' is a null pointer
-  logical, parameter :: test_Assoc6 = .not.(associated(null(), null(int_allocatable)))
 
   type A
     real(4) x

flang/test/Lower/HLFIR/null.f90

@@ -25,7 +25,6 @@ subroutine test2
   l = associated(null(),i)
 end subroutine test2
 ! CHECK-LABEL:   func.func @_QPtest2() {
-! CHECK:           %[[VAL_0:.*]] = fir.alloca !fir.box<!fir.ptr<none>>
 ! CHECK:           %[[VAL_1:.*]] = fir.alloca !fir.box<!fir.ptr<i32>> {bindc_name = "i", uniq_name = "_QFtest2Ei"}
 ! CHECK:           %[[VAL_2:.*]] = fir.zero_bits !fir.ptr<i32>
 ! CHECK:           %[[VAL_3:.*]] = fir.embox %[[VAL_2]] : (!fir.ptr<i32>) -> !fir.box<!fir.ptr<i32>>
@@ -33,16 +32,8 @@ end subroutine test2
 ! CHECK:           %[[VAL_4:.*]]:2 = hlfir.declare %[[VAL_1]] {fortran_attrs = #fir.var_attrs<pointer>, uniq_name = "_QFtest2Ei"} : (!fir.ref<!fir.box<!fir.ptr<i32>>>) -> (!fir.ref<!fir.box<!fir.ptr<i32>>>, !fir.ref<!fir.box<!fir.ptr<i32>>>)
 ! CHECK:           %[[VAL_5:.*]] = fir.alloca !fir.logical<4> {bindc_name = "l", uniq_name = "_QFtest2El"}
 ! CHECK:           %[[VAL_6:.*]]:2 = hlfir.declare %[[VAL_5]] {uniq_name = "_QFtest2El"} : (!fir.ref<!fir.logical<4>>) -> (!fir.ref<!fir.logical<4>>, !fir.ref<!fir.logical<4>>)
-! CHECK:           %[[VAL_7:.*]] = fir.zero_bits !fir.ptr<none>
+! CHECK:           %false = arith.constant false
-! CHECK:           %[[VAL_8:.*]] = fir.embox %[[VAL_7]] : (!fir.ptr<none>) -> !fir.box<!fir.ptr<none>>
+! CHECK:           %[[VAL_15:.*]] = fir.convert %false : (i1) -> !fir.logical<4>
-! CHECK:           fir.store %[[VAL_8]] to %[[VAL_0]] : !fir.ref<!fir.box<!fir.ptr<none>>>
-! CHECK:           %[[VAL_9:.*]]:2 = hlfir.declare %[[VAL_0]] {uniq_name = ".tmp.null_box"} : (!fir.ref<!fir.box<!fir.ptr<none>>>) -> (!fir.ref<!fir.box<!fir.ptr<none>>>, !fir.ref<!fir.box<!fir.ptr<none>>>)
-! CHECK:           %[[VAL_10:.*]] = fir.load %[[VAL_4]]#1 : !fir.ref<!fir.box<!fir.ptr<i32>>>
-! CHECK:           %[[VAL_11:.*]] = fir.load %[[VAL_9]]#1 : !fir.ref<!fir.box<!fir.ptr<none>>>
-! CHECK:           %[[VAL_12:.*]] = fir.convert %[[VAL_11]] : (!fir.box<!fir.ptr<none>>) -> !fir.box<none>
-! CHECK:           %[[VAL_13:.*]] = fir.convert %[[VAL_10]] : (!fir.box<!fir.ptr<i32>>) -> !fir.box<none>
-! CHECK:           %[[VAL_14:.*]] = fir.call @_FortranAPointerIsAssociatedWith(%[[VAL_12]], %[[VAL_13]]) fastmath<contract> : (!fir.box<none>, !fir.box<none>) -> i1
-! CHECK:           %[[VAL_15:.*]] = fir.convert %[[VAL_14]] : (i1) -> !fir.logical<4>
 ! CHECK:           hlfir.assign %[[VAL_15]] to %[[VAL_6]]#0 : !fir.logical<4>, !fir.ref<!fir.logical<4>>
 ! CHECK:           return
 ! CHECK:         }

flang/test/Semantics/associated.f90

@@ -119,7 +119,8 @@ subroutine assoc()
     lvar = associated(intPointerVar1, (targetIntVar1))
     !ERROR: MOLD= argument to NULL() must be a pointer or allocatable
     lVar = associated(null(intVar))
-    lVar = associated(null(intAllocVar)) !OK
+    !ERROR: A NULL() allocatable is not allowed for 'pointer=' intrinsic argument
+    lVar = associated(null(intAllocVar))
     lVar = associated(null()) !OK
     lVar = associated(null(intPointerVar1)) !OK
     !PORTABILITY: POINTER= argument of ASSOCIATED() is required by some other compilers to be a valid left-hand side of a pointer assignment statement

flang/test/Semantics/call27.f90

@@ -12,10 +12,9 @@ program test
   !ERROR: Actual argument associated with INTENT(IN OUT) dummy argument 'a=' is not definable
   !BECAUSE: 'null(mold=a)' is a null pointer
   call foo0(null(mold=a))
-  !WARNING: A null pointer should not be associated with allocatable dummy argument 'a=' without INTENT(IN)
+  !WARNING: A null allocatable should not be associated with allocatable dummy argument 'a=' without INTENT(IN)
   call foo1(null(mold=a))
-  !PORTABILITY: Allocatable dummy argument 'a=' is associated with a null pointer
+  call foo2(null(mold=a)) ! ok
-  call foo2(null(mold=a))
   call foo3(null(mold=a)) ! ok
  contains
   subroutine foo0(a)

flang/test/Semantics/null01.f90

@@ -112,7 +112,10 @@ subroutine test
   dt4x = dt4(null(dt2x%pps0))
   call canbenull(null(), null()) ! fine
   call canbenull(null(mold=ip0), null(mold=rp0)) ! fine
-  call optionalAllocatable(null(mold=ip0)) ! fine
+  !ERROR: ALLOCATABLE dummy argument 'x=' must be associated with an ALLOCATABLE actual argument
+  call optionalAllocatable(null(mold=ip0))
+  call optionalAllocatable(null(mold=ia0)) ! fine
+  call optionalAllocatable(null()) ! fine
   !ERROR: Null pointer argument requires an explicit interface
   call implicit(null())
   !ERROR: Null pointer argument requires an explicit interface