xref: /llvm-project/flang/lib/Evaluate/check-expression.cpp (revision 5a0382ce7ab3577630bdbb396e9ddaed8749101e) 
1 //===-- lib/Evaluate/check-expression.cpp ---------------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 
9 #include "flang/Evaluate/check-expression.h"
10 #include "flang/Evaluate/characteristics.h"
11 #include "flang/Evaluate/intrinsics.h"
12 #include "flang/Evaluate/tools.h"
13 #include "flang/Evaluate/traverse.h"
14 #include "flang/Evaluate/type.h"
15 #include "flang/Semantics/semantics.h"
16 #include "flang/Semantics/symbol.h"
17 #include "flang/Semantics/tools.h"
18 #include <set>
19 #include <string>
20 
21 namespace Fortran::evaluate {
22 
23 // Constant expression predicates IsConstantExpr() & IsScopeInvariantExpr().
24 // This code determines whether an expression is a "constant expression"
25 // in the sense of section 10.1.12.  This is not the same thing as being
26 // able to fold it (yet) into a known constant value; specifically,
27 // the expression may reference derived type kind parameters whose values
28 // are not yet known.
29 //
30 // The variant form (IsScopeInvariantExpr()) also accepts symbols that are
31 // INTENT(IN) dummy arguments without the VALUE attribute.
32 template <bool INVARIANT>
33 class IsConstantExprHelper
34     : public AllTraverse<IsConstantExprHelper<INVARIANT>, true> {
35 public:
36   using Base = AllTraverse<IsConstantExprHelper, true>;
37   IsConstantExprHelper() : Base{*this} {}
38   using Base::operator();
39 
40   // A missing expression is not considered to be constant.
41   template <typename A> bool operator()(const std::optional<A> &x) const {
42     return x && (*this)(*x);
43   }
44 
45   bool operator()(const TypeParamInquiry &inq) const {
46     return INVARIANT || semantics::IsKindTypeParameter(inq.parameter());
47   }
48   bool operator()(const semantics::Symbol &symbol) const {
49     const auto &ultimate{GetAssociationRoot(symbol)};
50     return IsNamedConstant(ultimate) || IsImpliedDoIndex(ultimate) ||
51         IsInitialProcedureTarget(ultimate) ||
52         ultimate.has<semantics::TypeParamDetails>() ||
53         (INVARIANT && IsIntentIn(symbol) && !IsOptional(symbol) &&
54             !symbol.attrs().test(semantics::Attr::VALUE));
55   }
56   bool operator()(const CoarrayRef &) const { return false; }
57   bool operator()(const semantics::ParamValue &param) const {
58     return param.isExplicit() && (*this)(param.GetExplicit());
59   }
60   bool operator()(const ProcedureRef &) const;
61   bool operator()(const StructureConstructor &constructor) const {
62     for (const auto &[symRef, expr] : constructor) {
63       if (!IsConstantStructureConstructorComponent(*symRef, expr.value())) {
64         return false;
65       }
66     }
67     return true;
68   }
69   bool operator()(const Component &component) const {
70     return (*this)(component.base());
71   }
72   // Forbid integer division by zero in constants.
73   template <int KIND>
74   bool operator()(
75       const Divide<Type<TypeCategory::Integer, KIND>> &division) const {
76     using T = Type<TypeCategory::Integer, KIND>;
77     if (const auto divisor{GetScalarConstantValue<T>(division.right())}) {
78       return !divisor->IsZero() && (*this)(division.left());
79     } else {
80       return false;
81     }
82   }
83 
84   bool operator()(const Constant<SomeDerived> &) const { return true; }
85   bool operator()(const DescriptorInquiry &x) const {
86     const Symbol &sym{x.base().GetLastSymbol()};
87     return INVARIANT && !IsAllocatable(sym) &&
88         (!IsDummy(sym) ||
89             (IsIntentIn(sym) && !IsOptional(sym) &&
90                 !sym.attrs().test(semantics::Attr::VALUE)));
91   }
92 
93 private:
94   bool IsConstantStructureConstructorComponent(
95       const Symbol &, const Expr<SomeType> &) const;
96   bool IsConstantExprShape(const Shape &) const;
97 };
98 
99 template <bool INVARIANT>
100 bool IsConstantExprHelper<INVARIANT>::IsConstantStructureConstructorComponent(
101     const Symbol &component, const Expr<SomeType> &expr) const {
102   if (IsAllocatable(component)) {
103     return IsNullObjectPointer(expr);
104   } else if (IsPointer(component)) {
105     return IsNullPointer(expr) || IsInitialDataTarget(expr) ||
106         IsInitialProcedureTarget(expr);
107   } else {
108     return (*this)(expr);
109   }
110 }
111 
112 template <bool INVARIANT>
113 bool IsConstantExprHelper<INVARIANT>::operator()(
114     const ProcedureRef &call) const {
115   // LBOUND, UBOUND, and SIZE with truly constant DIM= arguments will have
116   // been rewritten into DescriptorInquiry operations.
117   if (const auto *intrinsic{std::get_if<SpecificIntrinsic>(&call.proc().u)}) {
118     const characteristics::Procedure &proc{intrinsic->characteristics.value()};
119     if (intrinsic->name == "kind" ||
120         intrinsic->name == IntrinsicProcTable::InvalidName ||
121         call.arguments().empty() || !call.arguments()[0]) {
122       // kind is always a constant, and we avoid cascading errors by considering
123       // invalid calls to intrinsics to be constant
124       return true;
125     } else if (intrinsic->name == "lbound") {
126       auto base{ExtractNamedEntity(call.arguments()[0]->UnwrapExpr())};
127       return base && IsConstantExprShape(GetLBOUNDs(*base));
128     } else if (intrinsic->name == "ubound") {
129       auto base{ExtractNamedEntity(call.arguments()[0]->UnwrapExpr())};
130       return base && IsConstantExprShape(GetUBOUNDs(*base));
131     } else if (intrinsic->name == "shape" || intrinsic->name == "size") {
132       auto shape{GetShape(call.arguments()[0]->UnwrapExpr())};
133       return shape && IsConstantExprShape(*shape);
134     } else if (proc.IsPure()) {
135       for (const auto &arg : call.arguments()) {
136         if (!arg) {
137           return false;
138         } else if (const auto *expr{arg->UnwrapExpr()};
139                    !expr || !(*this)(*expr)) {
140           return false;
141         }
142       }
143       return true;
144     }
145     // TODO: STORAGE_SIZE
146   }
147   return false;
148 }
149 
150 template <bool INVARIANT>
151 bool IsConstantExprHelper<INVARIANT>::IsConstantExprShape(
152     const Shape &shape) const {
153   for (const auto &extent : shape) {
154     if (!(*this)(extent)) {
155       return false;
156     }
157   }
158   return true;
159 }
160 
161 template <typename A> bool IsConstantExpr(const A &x) {
162   return IsConstantExprHelper<false>{}(x);
163 }
164 template bool IsConstantExpr(const Expr<SomeType> &);
165 template bool IsConstantExpr(const Expr<SomeInteger> &);
166 template bool IsConstantExpr(const Expr<SubscriptInteger> &);
167 template bool IsConstantExpr(const StructureConstructor &);
168 
169 // IsScopeInvariantExpr()
170 template <typename A> bool IsScopeInvariantExpr(const A &x) {
171   return IsConstantExprHelper<true>{}(x);
172 }
173 template bool IsScopeInvariantExpr(const Expr<SomeType> &);
174 template bool IsScopeInvariantExpr(const Expr<SomeInteger> &);
175 template bool IsScopeInvariantExpr(const Expr<SubscriptInteger> &);
176 
177 // IsActuallyConstant()
178 struct IsActuallyConstantHelper {
179   template <typename A> bool operator()(const A &) { return false; }
180   template <typename T> bool operator()(const Constant<T> &) { return true; }
181   template <typename T> bool operator()(const Parentheses<T> &x) {
182     return (*this)(x.left());
183   }
184   template <typename T> bool operator()(const Expr<T> &x) {
185     return common::visit([=](const auto &y) { return (*this)(y); }, x.u);
186   }
187   bool operator()(const Expr<SomeType> &x) {
188     return common::visit([this](const auto &y) { return (*this)(y); }, x.u);
189   }
190   bool operator()(const StructureConstructor &x) {
191     for (const auto &pair : x) {
192       const Expr<SomeType> &y{pair.second.value()};
193       const auto sym{pair.first};
194       const bool compIsConstant{(*this)(y)};
195       // If an allocatable component is initialized by a constant,
196       // the structure constructor is not a constant.
197       if ((!compIsConstant && !IsNullPointer(y)) ||
198           (compIsConstant && IsAllocatable(sym))) {
199         return false;
200       }
201     }
202     return true;
203   }
204   template <typename A> bool operator()(const A *x) { return x && (*this)(*x); }
205   template <typename A> bool operator()(const std::optional<A> &x) {
206     return x && (*this)(*x);
207   }
208 };
209 
210 template <typename A> bool IsActuallyConstant(const A &x) {
211   return IsActuallyConstantHelper{}(x);
212 }
213 
214 template bool IsActuallyConstant(const Expr<SomeType> &);
215 template bool IsActuallyConstant(const Expr<SomeInteger> &);
216 template bool IsActuallyConstant(const Expr<SubscriptInteger> &);
217 template bool IsActuallyConstant(const std::optional<Expr<SubscriptInteger>> &);
218 
219 // Object pointer initialization checking predicate IsInitialDataTarget().
220 // This code determines whether an expression is allowable as the static
221 // data address used to initialize a pointer with "=> x".  See C765.
222 class IsInitialDataTargetHelper
223     : public AllTraverse<IsInitialDataTargetHelper, true> {
224 public:
225   using Base = AllTraverse<IsInitialDataTargetHelper, true>;
226   using Base::operator();
227   explicit IsInitialDataTargetHelper(parser::ContextualMessages *m)
228       : Base{*this}, messages_{m} {}
229 
230   bool emittedMessage() const { return emittedMessage_; }
231 
232   bool operator()(const BOZLiteralConstant &) const { return false; }
233   bool operator()(const NullPointer &) const { return true; }
234   template <typename T> bool operator()(const Constant<T> &) const {
235     return false;
236   }
237   bool operator()(const semantics::Symbol &symbol) {
238     // This function checks only base symbols, not components.
239     const Symbol &ultimate{symbol.GetUltimate()};
240     if (const auto *assoc{
241             ultimate.detailsIf<semantics::AssocEntityDetails>()}) {
242       if (const auto &expr{assoc->expr()}) {
243         if (IsVariable(*expr)) {
244           return (*this)(*expr);
245         } else if (messages_) {
246           messages_->Say(
247               "An initial data target may not be an associated expression ('%s')"_err_en_US,
248               ultimate.name());
249           emittedMessage_ = true;
250         }
251       }
252       return false;
253     } else if (!CheckVarOrComponent(ultimate)) {
254       return false;
255     } else if (!ultimate.attrs().test(semantics::Attr::TARGET)) {
256       if (messages_) {
257         messages_->Say(
258             "An initial data target may not be a reference to an object '%s' that lacks the TARGET attribute"_err_en_US,
259             ultimate.name());
260         emittedMessage_ = true;
261       }
262       return false;
263     } else if (!IsSaved(ultimate)) {
264       if (messages_) {
265         messages_->Say(
266             "An initial data target may not be a reference to an object '%s' that lacks the SAVE attribute"_err_en_US,
267             ultimate.name());
268         emittedMessage_ = true;
269       }
270       return false;
271     } else {
272       return true;
273     }
274   }
275   bool operator()(const StaticDataObject &) const { return false; }
276   bool operator()(const TypeParamInquiry &) const { return false; }
277   bool operator()(const Triplet &x) const {
278     return IsConstantExpr(x.lower()) && IsConstantExpr(x.upper()) &&
279         IsConstantExpr(x.stride());
280   }
281   bool operator()(const Subscript &x) const {
282     return common::visit(common::visitors{
283                              [&](const Triplet &t) { return (*this)(t); },
284                              [&](const auto &y) {
285                                return y.value().Rank() == 0 &&
286                                    IsConstantExpr(y.value());
287                              },
288                          },
289         x.u);
290   }
291   bool operator()(const CoarrayRef &) const { return false; }
292   bool operator()(const Component &x) {
293     return CheckVarOrComponent(x.GetLastSymbol()) && (*this)(x.base());
294   }
295   bool operator()(const Substring &x) const {
296     return IsConstantExpr(x.lower()) && IsConstantExpr(x.upper()) &&
297         (*this)(x.parent());
298   }
299   bool operator()(const DescriptorInquiry &) const { return false; }
300   template <typename T> bool operator()(const ArrayConstructor<T> &) const {
301     return false;
302   }
303   bool operator()(const StructureConstructor &) const { return false; }
304   template <typename D, typename R, typename... O>
305   bool operator()(const Operation<D, R, O...> &) const {
306     return false;
307   }
308   template <typename T> bool operator()(const Parentheses<T> &x) const {
309     return (*this)(x.left());
310   }
311   bool operator()(const ProcedureRef &x) const {
312     if (const SpecificIntrinsic * intrinsic{x.proc().GetSpecificIntrinsic()}) {
313       return intrinsic->characteristics.value().attrs.test(
314           characteristics::Procedure::Attr::NullPointer);
315     }
316     return false;
317   }
318   bool operator()(const Relational<SomeType> &) const { return false; }
319 
320 private:
321   bool CheckVarOrComponent(const semantics::Symbol &symbol) {
322     const Symbol &ultimate{symbol.GetUltimate()};
323     const char *unacceptable{nullptr};
324     if (ultimate.Corank() > 0) {
325       unacceptable = "a coarray";
326     } else if (IsAllocatable(ultimate)) {
327       unacceptable = "an ALLOCATABLE";
328     } else if (IsPointer(ultimate)) {
329       unacceptable = "a POINTER";
330     } else {
331       return true;
332     }
333     if (messages_) {
334       messages_->Say(
335           "An initial data target may not be a reference to %s '%s'"_err_en_US,
336           unacceptable, ultimate.name());
337       emittedMessage_ = true;
338     }
339     return false;
340   }
341 
342   parser::ContextualMessages *messages_;
343   bool emittedMessage_{false};
344 };
345 
346 bool IsInitialDataTarget(
347     const Expr<SomeType> &x, parser::ContextualMessages *messages) {
348   IsInitialDataTargetHelper helper{messages};
349   bool result{helper(x)};
350   if (!result && messages && !helper.emittedMessage()) {
351     messages->Say(
352         "An initial data target must be a designator with constant subscripts"_err_en_US);
353   }
354   return result;
355 }
356 
357 bool IsInitialProcedureTarget(const semantics::Symbol &symbol) {
358   const auto &ultimate{symbol.GetUltimate()};
359   return common::visit(
360       common::visitors{
361           [&](const semantics::SubprogramDetails &subp) {
362             return !subp.isDummy() && !subp.stmtFunction() &&
363                 symbol.owner().kind() != semantics::Scope::Kind::MainProgram &&
364                 symbol.owner().kind() != semantics::Scope::Kind::Subprogram;
365           },
366           [](const semantics::SubprogramNameDetails &x) {
367             return x.kind() != semantics::SubprogramKind::Internal;
368           },
369           [&](const semantics::ProcEntityDetails &proc) {
370             return !semantics::IsPointer(ultimate) && !proc.isDummy();
371           },
372           [](const auto &) { return false; },
373       },
374       ultimate.details());
375 }
376 
377 bool IsInitialProcedureTarget(const ProcedureDesignator &proc) {
378   if (const auto *intrin{proc.GetSpecificIntrinsic()}) {
379     return !intrin->isRestrictedSpecific;
380   } else if (proc.GetComponent()) {
381     return false;
382   } else {
383     return IsInitialProcedureTarget(DEREF(proc.GetSymbol()));
384   }
385 }
386 
387 bool IsInitialProcedureTarget(const Expr<SomeType> &expr) {
388   if (const auto *proc{std::get_if<ProcedureDesignator>(&expr.u)}) {
389     return IsInitialProcedureTarget(*proc);
390   } else {
391     return IsNullProcedurePointer(expr);
392   }
393 }
394 
395 // Converts, folds, and then checks type, rank, and shape of an
396 // initialization expression for a named constant, a non-pointer
397 // variable static initialization, a component default initializer,
398 // a type parameter default value, or instantiated type parameter value.
399 std::optional<Expr<SomeType>> NonPointerInitializationExpr(const Symbol &symbol,
400     Expr<SomeType> &&x, FoldingContext &context,
401     const semantics::Scope *instantiation) {
402   CHECK(!IsPointer(symbol));
403   if (auto symTS{
404           characteristics::TypeAndShape::Characterize(symbol, context)}) {
405     auto xType{x.GetType()};
406     auto converted{ConvertToType(symTS->type(), Expr<SomeType>{x})};
407     if (!converted &&
408         symbol.owner().context().IsEnabled(
409             common::LanguageFeature::LogicalIntegerAssignment)) {
410       converted = DataConstantConversionExtension(context, symTS->type(), x);
411       if (converted &&
412           symbol.owner().context().ShouldWarn(
413               common::LanguageFeature::LogicalIntegerAssignment)) {
414         context.messages().Say(
415             "nonstandard usage: initialization of %s with %s"_port_en_US,
416             symTS->type().AsFortran(), x.GetType().value().AsFortran());
417       }
418     }
419     if (converted) {
420       auto folded{Fold(context, std::move(*converted))};
421       if (IsActuallyConstant(folded)) {
422         int symRank{GetRank(symTS->shape())};
423         if (IsImpliedShape(symbol)) {
424           if (folded.Rank() == symRank) {
425             return ArrayConstantBoundChanger{
426                 std::move(*AsConstantExtents(
427                     context, GetRawLowerBounds(context, NamedEntity{symbol})))}
428                 .ChangeLbounds(std::move(folded));
429           } else {
430             context.messages().Say(
431                 "Implied-shape parameter '%s' has rank %d but its initializer has rank %d"_err_en_US,
432                 symbol.name(), symRank, folded.Rank());
433           }
434         } else if (auto extents{AsConstantExtents(context, symTS->shape())}) {
435           if (folded.Rank() == 0 && symRank == 0) {
436             // symbol and constant are both scalars
437             return {std::move(folded)};
438           } else if (folded.Rank() == 0 && symRank > 0) {
439             // expand the scalar constant to an array
440             return ScalarConstantExpander{std::move(*extents),
441                 AsConstantExtents(
442                     context, GetRawLowerBounds(context, NamedEntity{symbol}))}
443                 .Expand(std::move(folded));
444           } else if (auto resultShape{GetShape(context, folded)}) {
445             if (CheckConformance(context.messages(), symTS->shape(),
446                     *resultShape, CheckConformanceFlags::None,
447                     "initialized object", "initialization expression")
448                     .value_or(false /*fail if not known now to conform*/)) {
449               // make a constant array with adjusted lower bounds
450               return ArrayConstantBoundChanger{
451                   std::move(*AsConstantExtents(context,
452                       GetRawLowerBounds(context, NamedEntity{symbol})))}
453                   .ChangeLbounds(std::move(folded));
454             }
455           }
456         } else if (IsNamedConstant(symbol)) {
457           if (IsExplicitShape(symbol)) {
458             context.messages().Say(
459                 "Named constant '%s' array must have constant shape"_err_en_US,
460                 symbol.name());
461           } else {
462             // Declaration checking handles other cases
463           }
464         } else {
465           context.messages().Say(
466               "Shape of initialized object '%s' must be constant"_err_en_US,
467               symbol.name());
468         }
469       } else if (IsErrorExpr(folded)) {
470       } else if (IsLenTypeParameter(symbol)) {
471         return {std::move(folded)};
472       } else if (IsKindTypeParameter(symbol)) {
473         if (instantiation) {
474           context.messages().Say(
475               "Value of kind type parameter '%s' (%s) must be a scalar INTEGER constant"_err_en_US,
476               symbol.name(), folded.AsFortran());
477         } else {
478           return {std::move(folded)};
479         }
480       } else if (IsNamedConstant(symbol)) {
481         context.messages().Say(
482             "Value of named constant '%s' (%s) cannot be computed as a constant value"_err_en_US,
483             symbol.name(), folded.AsFortran());
484       } else {
485         context.messages().Say(
486             "Initialization expression for '%s' (%s) cannot be computed as a constant value"_err_en_US,
487             symbol.name(), folded.AsFortran());
488       }
489     } else if (xType) {
490       context.messages().Say(
491           "Initialization expression cannot be converted to declared type of '%s' from %s"_err_en_US,
492           symbol.name(), xType->AsFortran());
493     } else {
494       context.messages().Say(
495           "Initialization expression cannot be converted to declared type of '%s'"_err_en_US,
496           symbol.name());
497     }
498   }
499   return std::nullopt;
500 }
501 
502 static bool IsNonLocal(const semantics::Symbol &symbol) {
503   return semantics::IsDummy(symbol) || symbol.has<semantics::UseDetails>() ||
504       symbol.owner().kind() == semantics::Scope::Kind::Module ||
505       semantics::FindCommonBlockContaining(symbol) ||
506       symbol.has<semantics::HostAssocDetails>();
507 }
508 
509 static bool IsPermissibleInquiry(const semantics::Symbol &firstSymbol,
510     const semantics::Symbol &lastSymbol, DescriptorInquiry::Field field,
511     const semantics::Scope &localScope) {
512   if (IsNonLocal(firstSymbol)) {
513     return true;
514   }
515   if (&localScope != &firstSymbol.owner()) {
516     return true;
517   }
518   // Inquiries on local objects may not access a deferred bound or length.
519   // (This code used to be a switch, but it proved impossible to write it
520   // thus without running afoul of bogus warnings from different C++
521   // compilers.)
522   if (field == DescriptorInquiry::Field::Rank) {
523     return true; // always known
524   }
525   const auto *object{lastSymbol.detailsIf<semantics::ObjectEntityDetails>()};
526   if (field == DescriptorInquiry::Field::LowerBound ||
527       field == DescriptorInquiry::Field::Extent ||
528       field == DescriptorInquiry::Field::Stride) {
529     return object && !object->shape().CanBeDeferredShape();
530   }
531   if (field == DescriptorInquiry::Field::Len) {
532     return object && object->type() &&
533         object->type()->category() == semantics::DeclTypeSpec::Character &&
534         !object->type()->characterTypeSpec().length().isDeferred();
535   }
536   return false;
537 }
538 
539 // Specification expression validation (10.1.11(2), C1010)
540 class CheckSpecificationExprHelper
541     : public AnyTraverse<CheckSpecificationExprHelper,
542           std::optional<std::string>> {
543 public:
544   using Result = std::optional<std::string>;
545   using Base = AnyTraverse<CheckSpecificationExprHelper, Result>;
546   explicit CheckSpecificationExprHelper(
547       const semantics::Scope &s, FoldingContext &context)
548       : Base{*this}, scope_{s}, context_{context} {}
549   using Base::operator();
550 
551   Result operator()(const CoarrayRef &) const { return "coindexed reference"; }
552 
553   Result operator()(const semantics::Symbol &symbol) const {
554     const auto &ultimate{symbol.GetUltimate()};
555     if (const auto *assoc{
556             ultimate.detailsIf<semantics::AssocEntityDetails>()}) {
557       return (*this)(assoc->expr());
558     } else if (semantics::IsNamedConstant(ultimate) ||
559         ultimate.owner().IsModule() || ultimate.owner().IsSubmodule()) {
560       return std::nullopt;
561     } else if (scope_.IsDerivedType() &&
562         IsVariableName(ultimate)) { // C750, C754
563       return "derived type component or type parameter value not allowed to "
564              "reference variable '"s +
565           ultimate.name().ToString() + "'";
566     } else if (IsDummy(ultimate)) {
567       if (ultimate.attrs().test(semantics::Attr::OPTIONAL)) {
568         return "reference to OPTIONAL dummy argument '"s +
569             ultimate.name().ToString() + "'";
570       } else if (!inInquiry_ &&
571           ultimate.attrs().test(semantics::Attr::INTENT_OUT)) {
572         return "reference to INTENT(OUT) dummy argument '"s +
573             ultimate.name().ToString() + "'";
574       } else if (ultimate.has<semantics::ObjectEntityDetails>()) {
575         return std::nullopt;
576       } else {
577         return "dummy procedure argument";
578       }
579     } else if (&symbol.owner() != &scope_ || &ultimate.owner() != &scope_) {
580       return std::nullopt; // host association is in play
581     } else if (const auto *object{
582                    ultimate.detailsIf<semantics::ObjectEntityDetails>()}) {
583       if (object->commonBlock()) {
584         return std::nullopt;
585       }
586     }
587     if (inInquiry_) {
588       return std::nullopt;
589     } else {
590       return "reference to local entity '"s + ultimate.name().ToString() + "'";
591     }
592   }
593 
594   Result operator()(const Component &x) const {
595     // Don't look at the component symbol.
596     return (*this)(x.base());
597   }
598   Result operator()(const ArrayRef &x) const {
599     if (auto result{(*this)(x.base())}) {
600       return result;
601     }
602     // The subscripts don't get special protection for being in a
603     // specification inquiry context;
604     auto restorer{common::ScopedSet(inInquiry_, false)};
605     return (*this)(x.subscript());
606   }
607   Result operator()(const Substring &x) const {
608     if (auto result{(*this)(x.parent())}) {
609       return result;
610     }
611     // The bounds don't get special protection for being in a
612     // specification inquiry context;
613     auto restorer{common::ScopedSet(inInquiry_, false)};
614     if (auto result{(*this)(x.lower())}) {
615       return result;
616     }
617     return (*this)(x.upper());
618   }
619   Result operator()(const DescriptorInquiry &x) const {
620     // Many uses of SIZE(), LBOUND(), &c. that are valid in specification
621     // expressions will have been converted to expressions over descriptor
622     // inquiries by Fold().
623     // Catch REAL, ALLOCATABLE :: X(:); REAL :: Y(SIZE(X))
624     if (IsPermissibleInquiry(x.base().GetFirstSymbol(),
625             x.base().GetLastSymbol(), x.field(), scope_)) {
626       auto restorer{common::ScopedSet(inInquiry_, true)};
627       return (*this)(x.base());
628     } else if (IsConstantExpr(x)) {
629       return std::nullopt;
630     } else {
631       return "non-constant descriptor inquiry not allowed for local object";
632     }
633   }
634 
635   Result operator()(const TypeParamInquiry &inq) const {
636     if (scope_.IsDerivedType() && !IsConstantExpr(inq) &&
637         inq.base() /* X%T, not local T */) { // C750, C754
638       return "non-constant reference to a type parameter inquiry not "
639              "allowed for derived type components or type parameter values";
640     }
641     return std::nullopt;
642   }
643 
644   Result operator()(const ProcedureRef &x) const {
645     bool inInquiry{false};
646     if (const auto *symbol{x.proc().GetSymbol()}) {
647       const Symbol &ultimate{symbol->GetUltimate()};
648       if (!semantics::IsPureProcedure(ultimate)) {
649         return "reference to impure function '"s + ultimate.name().ToString() +
650             "'";
651       }
652       if (semantics::IsStmtFunction(ultimate)) {
653         return "reference to statement function '"s +
654             ultimate.name().ToString() + "'";
655       }
656       if (scope_.IsDerivedType()) { // C750, C754
657         return "reference to function '"s + ultimate.name().ToString() +
658             "' not allowed for derived type components or type parameter"
659             " values";
660       }
661       if (auto procChars{
662               characteristics::Procedure::Characterize(x.proc(), context_)}) {
663         const auto iter{std::find_if(procChars->dummyArguments.begin(),
664             procChars->dummyArguments.end(),
665             [](const characteristics::DummyArgument &dummy) {
666               return std::holds_alternative<characteristics::DummyProcedure>(
667                   dummy.u);
668             })};
669         if (iter != procChars->dummyArguments.end()) {
670           return "reference to function '"s + ultimate.name().ToString() +
671               "' with dummy procedure argument '" + iter->name + '\'';
672         }
673       }
674       // References to internal functions are caught in expression semantics.
675       // TODO: other checks for standard module procedures
676     } else { // intrinsic
677       const SpecificIntrinsic &intrin{DEREF(x.proc().GetSpecificIntrinsic())};
678       inInquiry = context_.intrinsics().GetIntrinsicClass(intrin.name) ==
679           IntrinsicClass::inquiryFunction;
680       if (scope_.IsDerivedType()) { // C750, C754
681         if ((context_.intrinsics().IsIntrinsic(intrin.name) &&
682                 badIntrinsicsForComponents_.find(intrin.name) !=
683                     badIntrinsicsForComponents_.end())) {
684           return "reference to intrinsic '"s + intrin.name +
685               "' not allowed for derived type components or type parameter"
686               " values";
687         }
688         if (inInquiry && !IsConstantExpr(x)) {
689           return "non-constant reference to inquiry intrinsic '"s +
690               intrin.name +
691               "' not allowed for derived type components or type"
692               " parameter values";
693         }
694       }
695       // Type-determined inquiries (DIGITS, HUGE, &c.) will have already been
696       // folded and won't arrive here.  Inquiries that are represented with
697       // DescriptorInquiry operations (LBOUND) are checked elsewhere.  If a
698       // call that makes it to here satisfies the requirements of a constant
699       // expression (as Fortran defines it), it's fine.
700       if (IsConstantExpr(x)) {
701         return std::nullopt;
702       }
703       if (intrin.name == "present") {
704         return std::nullopt; // always ok
705       }
706       // Catch CHARACTER(:), ALLOCATABLE :: X; CHARACTER(LEN(X)) :: Y
707       if (inInquiry && x.arguments().size() >= 1) {
708         if (const auto &arg{x.arguments().at(0)}) {
709           if (auto dataRef{ExtractDataRef(*arg, true, true)}) {
710             if (intrin.name == "allocated" || intrin.name == "associated" ||
711                 intrin.name == "is_contiguous") { // ok
712             } else if (intrin.name == "len" &&
713                 IsPermissibleInquiry(dataRef->GetFirstSymbol(),
714                     dataRef->GetLastSymbol(), DescriptorInquiry::Field::Len,
715                     scope_)) { // ok
716             } else if (intrin.name == "lbound" &&
717                 IsPermissibleInquiry(dataRef->GetFirstSymbol(),
718                     dataRef->GetLastSymbol(),
719                     DescriptorInquiry::Field::LowerBound, scope_)) { // ok
720             } else if ((intrin.name == "shape" || intrin.name == "size" ||
721                            intrin.name == "sizeof" ||
722                            intrin.name == "storage_size" ||
723                            intrin.name == "ubound") &&
724                 IsPermissibleInquiry(dataRef->GetFirstSymbol(),
725                     dataRef->GetLastSymbol(), DescriptorInquiry::Field::Extent,
726                     scope_)) { // ok
727             } else {
728               return "non-constant inquiry function '"s + intrin.name +
729                   "' not allowed for local object";
730             }
731           }
732         }
733       }
734     }
735     auto restorer{common::ScopedSet(inInquiry_, inInquiry)};
736     return (*this)(x.arguments());
737   }
738 
739 private:
740   const semantics::Scope &scope_;
741   FoldingContext &context_;
742   // Contextual information: this flag is true when in an argument to
743   // an inquiry intrinsic like SIZE().
744   mutable bool inInquiry_{false};
745   const std::set<std::string> badIntrinsicsForComponents_{
746       "allocated", "associated", "extends_type_of", "present", "same_type_as"};
747 };
748 
749 template <typename A>
750 void CheckSpecificationExpr(
751     const A &x, const semantics::Scope &scope, FoldingContext &context) {
752   if (auto why{CheckSpecificationExprHelper{scope, context}(x)}) {
753     context.messages().Say(
754         "Invalid specification expression: %s"_err_en_US, *why);
755   }
756 }
757 
758 template void CheckSpecificationExpr(
759     const Expr<SomeType> &, const semantics::Scope &, FoldingContext &);
760 template void CheckSpecificationExpr(
761     const Expr<SomeInteger> &, const semantics::Scope &, FoldingContext &);
762 template void CheckSpecificationExpr(
763     const Expr<SubscriptInteger> &, const semantics::Scope &, FoldingContext &);
764 template void CheckSpecificationExpr(const std::optional<Expr<SomeType>> &,
765     const semantics::Scope &, FoldingContext &);
766 template void CheckSpecificationExpr(const std::optional<Expr<SomeInteger>> &,
767     const semantics::Scope &, FoldingContext &);
768 template void CheckSpecificationExpr(
769     const std::optional<Expr<SubscriptInteger>> &, const semantics::Scope &,
770     FoldingContext &);
771 
772 // IsContiguous() -- 9.5.4
773 class IsContiguousHelper
774     : public AnyTraverse<IsContiguousHelper, std::optional<bool>> {
775 public:
776   using Result = std::optional<bool>; // tri-state
777   using Base = AnyTraverse<IsContiguousHelper, Result>;
778   explicit IsContiguousHelper(FoldingContext &c) : Base{*this}, context_{c} {}
779   using Base::operator();
780 
781   template <typename T> Result operator()(const Constant<T> &) const {
782     return true;
783   }
784   Result operator()(const StaticDataObject &) const { return true; }
785   Result operator()(const semantics::Symbol &symbol) const {
786     const auto &ultimate{symbol.GetUltimate()};
787     if (ultimate.attrs().test(semantics::Attr::CONTIGUOUS)) {
788       return true;
789     } else if (!IsVariable(symbol)) {
790       return true;
791     } else if (ultimate.Rank() == 0) {
792       // Extension: accept scalars as a degenerate case of
793       // simple contiguity to allow their use in contexts like
794       // data targets in pointer assignments with remapping.
795       return true;
796     } else if (ultimate.has<semantics::AssocEntityDetails>()) {
797       return Base::operator()(ultimate); // use expr
798     } else if (semantics::IsPointer(ultimate) ||
799         semantics::IsAssumedShape(ultimate) || IsAssumedRank(ultimate)) {
800       return std::nullopt;
801     } else if (ultimate.has<semantics::ObjectEntityDetails>()) {
802       return true;
803     } else {
804       return Base::operator()(ultimate);
805     }
806   }
807 
808   Result operator()(const ArrayRef &x) const {
809     if (x.Rank() == 0) {
810       return true; // scalars considered contiguous
811     }
812     int subscriptRank{0};
813     auto baseLbounds{GetLBOUNDs(context_, x.base())};
814     auto baseUbounds{GetUBOUNDs(context_, x.base())};
815     auto subscripts{CheckSubscripts(
816         x.subscript(), subscriptRank, &baseLbounds, &baseUbounds)};
817     if (!subscripts.value_or(false)) {
818       return subscripts; // subscripts not known to be contiguous
819     } else if (subscriptRank > 0) {
820       // a(1)%b(:,:) is contiguous if and only if a(1)%b is contiguous.
821       return (*this)(x.base());
822     } else {
823       // a(:)%b(1,1) is (probably) not contiguous.
824       return std::nullopt;
825     }
826   }
827   Result operator()(const CoarrayRef &x) const {
828     int rank{0};
829     return CheckSubscripts(x.subscript(), rank).has_value();
830   }
831   Result operator()(const Component &x) const {
832     if (x.base().Rank() == 0) {
833       return (*this)(x.GetLastSymbol());
834     } else {
835       if (Result baseIsContiguous{(*this)(x.base())}) {
836         if (!*baseIsContiguous) {
837           return false;
838         }
839         // TODO could be true if base contiguous and this is only component, or
840         // if base has only one element?
841       }
842       return std::nullopt;
843     }
844   }
845   Result operator()(const ComplexPart &x) const {
846     return x.complex().Rank() == 0;
847   }
848   Result operator()(const Substring &) const { return std::nullopt; }
849 
850   Result operator()(const ProcedureRef &x) const {
851     if (auto chars{
852             characteristics::Procedure::Characterize(x.proc(), context_)}) {
853       if (chars->functionResult) {
854         const auto &result{*chars->functionResult};
855         if (!result.IsProcedurePointer()) {
856           if (result.attrs.test(
857                   characteristics::FunctionResult::Attr::Contiguous)) {
858             return true;
859           }
860           if (!result.attrs.test(
861                   characteristics::FunctionResult::Attr::Pointer)) {
862             return true;
863           }
864           if (const auto *type{result.GetTypeAndShape()};
865               type && type->Rank() == 0) {
866             return true; // pointer to scalar
867           }
868           // Must be non-CONTIGUOUS pointer to array
869         }
870       }
871     }
872     return std::nullopt;
873   }
874 
875   Result operator()(const NullPointer &) const { return true; }
876 
877 private:
878   // Returns "true" for a provably empty or simply contiguous array section;
879   // return "false" for a provably nonempty discontiguous section or for use
880   // of a vector subscript.
881   std::optional<bool> CheckSubscripts(const std::vector<Subscript> &subscript,
882       int &rank, const Shape *baseLbounds = nullptr,
883       const Shape *baseUbounds = nullptr) const {
884     bool anyTriplet{false};
885     rank = 0;
886     // Detect any provably empty dimension in this array section, which would
887     // render the whole section empty and therefore vacuously contiguous.
888     std::optional<bool> result;
889     bool mayBeEmpty{false};
890     auto dims{subscript.size()};
891     std::vector<bool> knownPartialSlice(dims, false);
892     for (auto j{dims}; j-- > 0;) {
893       std::optional<ConstantSubscript> dimLbound;
894       std::optional<ConstantSubscript> dimUbound;
895       std::optional<ConstantSubscript> dimExtent;
896       if (baseLbounds && j < baseLbounds->size()) {
897         if (const auto &lb{baseLbounds->at(j)}) {
898           dimLbound = ToInt64(Fold(context_, Expr<SubscriptInteger>{*lb}));
899         }
900       }
901       if (baseUbounds && j < baseUbounds->size()) {
902         if (const auto &ub{baseUbounds->at(j)}) {
903           dimUbound = ToInt64(Fold(context_, Expr<SubscriptInteger>{*ub}));
904         }
905       }
906       if (dimLbound && dimUbound) {
907         if (*dimLbound <= *dimUbound) {
908           dimExtent = *dimUbound - *dimLbound + 1;
909         } else {
910           // This is an empty dimension.
911           result = true;
912           dimExtent = 0;
913         }
914       }
915 
916       if (const auto *triplet{std::get_if<Triplet>(&subscript[j].u)}) {
917         ++rank;
918         if (auto stride{ToInt64(triplet->stride())}) {
919           const Expr<SubscriptInteger> *lowerBound{triplet->GetLower()};
920           const Expr<SubscriptInteger> *upperBound{triplet->GetUpper()};
921           std::optional<ConstantSubscript> lowerVal{lowerBound
922                   ? ToInt64(Fold(context_, Expr<SubscriptInteger>{*lowerBound}))
923                   : dimLbound};
924           std::optional<ConstantSubscript> upperVal{upperBound
925                   ? ToInt64(Fold(context_, Expr<SubscriptInteger>{*upperBound}))
926                   : dimUbound};
927           if (lowerVal && upperVal) {
928             if (*lowerVal < *upperVal) {
929               if (*stride < 0) {
930                 result = true; // empty dimension
931               } else if (!result && *stride > 1 &&
932                   *lowerVal + *stride <= *upperVal) {
933                 result = false; // discontiguous if not empty
934               }
935             } else if (*lowerVal > *upperVal) {
936               if (*stride > 0) {
937                 result = true; // empty dimension
938               } else if (!result && *stride < 0 &&
939                   *lowerVal + *stride >= *upperVal) {
940                 result = false; // discontiguous if not empty
941               }
942             } else {
943               mayBeEmpty = true;
944             }
945           } else {
946             mayBeEmpty = true;
947           }
948         } else {
949           mayBeEmpty = true;
950         }
951       } else if (subscript[j].Rank() > 0) {
952         ++rank;
953         if (!result) {
954           result = false; // vector subscript
955         }
956         mayBeEmpty = true;
957       } else {
958         // Scalar subscript.
959         if (dimExtent && *dimExtent > 1) {
960           knownPartialSlice[j] = true;
961         }
962       }
963     }
964     if (rank == 0) {
965       result = true; // scalar
966     }
967     if (result) {
968       return result;
969     }
970     // Not provably discontiguous at this point.
971     // Return "true" if simply contiguous, otherwise nullopt.
972     for (auto j{subscript.size()}; j-- > 0;) {
973       if (const auto *triplet{std::get_if<Triplet>(&subscript[j].u)}) {
974         auto stride{ToInt64(triplet->stride())};
975         if (!stride || stride != 1) {
976           return std::nullopt;
977         } else if (anyTriplet) {
978           if (triplet->GetLower() || triplet->GetUpper()) {
979             // all triplets before the last one must be just ":" for
980             // simple contiguity
981             return std::nullopt;
982           }
983         } else {
984           anyTriplet = true;
985         }
986         ++rank;
987       } else if (anyTriplet) {
988         // If the section cannot be empty, and this dimension's
989         // scalar subscript is known not to cover the whole
990         // dimension, then the array section is provably
991         // discontiguous.
992         return (mayBeEmpty || !knownPartialSlice[j])
993             ? std::nullopt
994             : std::make_optional(false);
995       }
996     }
997     return true; // simply contiguous
998   }
999 
1000   FoldingContext &context_;
1001 };
1002 
1003 template <typename A>
1004 std::optional<bool> IsContiguous(const A &x, FoldingContext &context) {
1005   return IsContiguousHelper{context}(x);
1006 }
1007 
1008 template std::optional<bool> IsContiguous(
1009     const Expr<SomeType> &, FoldingContext &);
1010 template std::optional<bool> IsContiguous(const ArrayRef &, FoldingContext &);
1011 template std::optional<bool> IsContiguous(const Substring &, FoldingContext &);
1012 template std::optional<bool> IsContiguous(const Component &, FoldingContext &);
1013 template std::optional<bool> IsContiguous(
1014     const ComplexPart &, FoldingContext &);
1015 template std::optional<bool> IsContiguous(const CoarrayRef &, FoldingContext &);
1016 template std::optional<bool> IsContiguous(const Symbol &, FoldingContext &);
1017 
1018 // IsErrorExpr()
1019 struct IsErrorExprHelper : public AnyTraverse<IsErrorExprHelper, bool> {
1020   using Result = bool;
1021   using Base = AnyTraverse<IsErrorExprHelper, Result>;
1022   IsErrorExprHelper() : Base{*this} {}
1023   using Base::operator();
1024 
1025   bool operator()(const SpecificIntrinsic &x) {
1026     return x.name == IntrinsicProcTable::InvalidName;
1027   }
1028 };
1029 
1030 template <typename A> bool IsErrorExpr(const A &x) {
1031   return IsErrorExprHelper{}(x);
1032 }
1033 
1034 template bool IsErrorExpr(const Expr<SomeType> &);
1035 
1036 // C1577
1037 // TODO: Also check C1579 & C1582 here
1038 class StmtFunctionChecker
1039     : public AnyTraverse<StmtFunctionChecker, std::optional<parser::Message>> {
1040 public:
1041   using Result = std::optional<parser::Message>;
1042   using Base = AnyTraverse<StmtFunctionChecker, Result>;
1043   StmtFunctionChecker(const Symbol &sf, FoldingContext &context)
1044       : Base{*this}, sf_{sf}, context_{context} {
1045     if (!context_.languageFeatures().IsEnabled(
1046             common::LanguageFeature::StatementFunctionExtensions)) {
1047       severity_ = parser::Severity::Error;
1048     } else if (context_.languageFeatures().ShouldWarn(
1049                    common::LanguageFeature::StatementFunctionExtensions)) {
1050       severity_ = parser::Severity::Portability;
1051     }
1052   }
1053   using Base::operator();
1054 
1055   template <typename T> Result operator()(const ArrayConstructor<T> &) const {
1056     if (severity_) {
1057       auto msg{
1058           "Statement function '%s' should not contain an array constructor"_port_en_US};
1059       msg.set_severity(*severity_);
1060       return parser::Message{sf_.name(), std::move(msg), sf_.name()};
1061     } else {
1062       return std::nullopt;
1063     }
1064   }
1065   Result operator()(const StructureConstructor &) const {
1066     if (severity_) {
1067       auto msg{
1068           "Statement function '%s' should not contain a structure constructor"_port_en_US};
1069       msg.set_severity(*severity_);
1070       return parser::Message{sf_.name(), std::move(msg), sf_.name()};
1071     } else {
1072       return std::nullopt;
1073     }
1074   }
1075   Result operator()(const TypeParamInquiry &) const {
1076     if (severity_) {
1077       auto msg{
1078           "Statement function '%s' should not contain a type parameter inquiry"_port_en_US};
1079       msg.set_severity(*severity_);
1080       return parser::Message{sf_.name(), std::move(msg), sf_.name()};
1081     } else {
1082       return std::nullopt;
1083     }
1084   }
1085   Result operator()(const ProcedureDesignator &proc) const {
1086     if (const Symbol * symbol{proc.GetSymbol()}) {
1087       const Symbol &ultimate{symbol->GetUltimate()};
1088       if (const auto *subp{
1089               ultimate.detailsIf<semantics::SubprogramDetails>()}) {
1090         if (subp->stmtFunction() && &ultimate.owner() == &sf_.owner()) {
1091           if (ultimate.name().begin() > sf_.name().begin()) {
1092             return parser::Message{sf_.name(),
1093                 "Statement function '%s' may not reference another statement function '%s' that is defined later"_err_en_US,
1094                 sf_.name(), ultimate.name()};
1095           }
1096         }
1097       }
1098       if (auto chars{
1099               characteristics::Procedure::Characterize(proc, context_)}) {
1100         if (!chars->CanBeCalledViaImplicitInterface()) {
1101           if (severity_) {
1102             auto msg{
1103                 "Statement function '%s' should not reference function '%s' that requires an explicit interface"_port_en_US};
1104             msg.set_severity(*severity_);
1105             return parser::Message{
1106                 sf_.name(), std::move(msg), sf_.name(), symbol->name()};
1107           }
1108         }
1109       }
1110     }
1111     if (proc.Rank() > 0) {
1112       if (severity_) {
1113         auto msg{
1114             "Statement function '%s' should not reference a function that returns an array"_port_en_US};
1115         msg.set_severity(*severity_);
1116         return parser::Message{sf_.name(), std::move(msg), sf_.name()};
1117       }
1118     }
1119     return std::nullopt;
1120   }
1121   Result operator()(const ActualArgument &arg) const {
1122     if (const auto *expr{arg.UnwrapExpr()}) {
1123       if (auto result{(*this)(*expr)}) {
1124         return result;
1125       }
1126       if (expr->Rank() > 0 && !UnwrapWholeSymbolOrComponentDataRef(*expr)) {
1127         if (severity_) {
1128           auto msg{
1129               "Statement function '%s' should not pass an array argument that is not a whole array"_port_en_US};
1130           msg.set_severity(*severity_);
1131           return parser::Message{sf_.name(), std::move(msg), sf_.name()};
1132         }
1133       }
1134     }
1135     return std::nullopt;
1136   }
1137 
1138 private:
1139   const Symbol &sf_;
1140   FoldingContext &context_;
1141   std::optional<parser::Severity> severity_;
1142 };
1143 
1144 std::optional<parser::Message> CheckStatementFunction(
1145     const Symbol &sf, const Expr<SomeType> &expr, FoldingContext &context) {
1146   return StmtFunctionChecker{sf, context}(expr);
1147 }
1148 
1149 } // namespace Fortran::evaluate
1150