xref: /llvm-project/flang/lib/Evaluate/characteristics.cpp (revision 95f4ca7f5db623bacc2e34548d39fe5b28d47bad) 
1 //===-- lib/Evaluate/characteristics.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/characteristics.h"
10 #include "flang/Common/indirection.h"
11 #include "flang/Evaluate/check-expression.h"
12 #include "flang/Evaluate/fold.h"
13 #include "flang/Evaluate/intrinsics.h"
14 #include "flang/Evaluate/tools.h"
15 #include "flang/Evaluate/type.h"
16 #include "flang/Parser/message.h"
17 #include "flang/Semantics/scope.h"
18 #include "flang/Semantics/symbol.h"
19 #include "flang/Semantics/tools.h"
20 #include "llvm/Support/raw_ostream.h"
21 #include <initializer_list>
22 
23 using namespace Fortran::parser::literals;
24 
25 namespace Fortran::evaluate::characteristics {
26 
27 // Copy attributes from a symbol to dst based on the mapping in pairs.
28 template <typename A, typename B>
29 static void CopyAttrs(const semantics::Symbol &src, A &dst,
30     const std::initializer_list<std::pair<semantics::Attr, B>> &pairs) {
31   for (const auto &pair : pairs) {
32     if (src.attrs().test(pair.first)) {
33       dst.attrs.set(pair.second);
34     }
35   }
36 }
37 
38 // Shapes of function results and dummy arguments have to have
39 // the same rank, the same deferred dimensions, and the same
40 // values for explicit dimensions when constant.
41 bool ShapesAreCompatible(const Shape &x, const Shape &y) {
42   if (x.size() != y.size()) {
43     return false;
44   }
45   auto yIter{y.begin()};
46   for (const auto &xDim : x) {
47     const auto &yDim{*yIter++};
48     if (xDim) {
49       if (!yDim || ToInt64(*xDim) != ToInt64(*yDim)) {
50         return false;
51       }
52     } else if (yDim) {
53       return false;
54     }
55   }
56   return true;
57 }
58 
59 bool TypeAndShape::operator==(const TypeAndShape &that) const {
60   return type_ == that.type_ && ShapesAreCompatible(shape_, that.shape_) &&
61       attrs_ == that.attrs_ && corank_ == that.corank_;
62 }
63 
64 TypeAndShape &TypeAndShape::Rewrite(FoldingContext &context) {
65   LEN_ = Fold(context, std::move(LEN_));
66   shape_ = Fold(context, std::move(shape_));
67   return *this;
68 }
69 
70 std::optional<TypeAndShape> TypeAndShape::Characterize(
71     const semantics::Symbol &symbol, FoldingContext &context) {
72   const auto &ultimate{symbol.GetUltimate()};
73   return common::visit(
74       common::visitors{
75           [&](const semantics::ProcEntityDetails &proc) {
76             const semantics::ProcInterface &interface { proc.interface() };
77             if (interface.type()) {
78               return Characterize(*interface.type(), context);
79             } else if (interface.symbol()) {
80               return Characterize(*interface.symbol(), context);
81             } else {
82               return std::optional<TypeAndShape>{};
83             }
84           },
85           [&](const semantics::AssocEntityDetails &assoc) {
86             return Characterize(assoc, context);
87           },
88           [&](const semantics::ProcBindingDetails &binding) {
89             return Characterize(binding.symbol(), context);
90           },
91           [&](const auto &x) -> std::optional<TypeAndShape> {
92             using Ty = std::decay_t<decltype(x)>;
93             if constexpr (std::is_same_v<Ty, semantics::EntityDetails> ||
94                 std::is_same_v<Ty, semantics::ObjectEntityDetails> ||
95                 std::is_same_v<Ty, semantics::TypeParamDetails>) {
96               if (const semantics::DeclTypeSpec * type{ultimate.GetType()}) {
97                 if (auto dyType{DynamicType::From(*type)}) {
98                   TypeAndShape result{
99                       std::move(*dyType), GetShape(context, ultimate)};
100                   result.AcquireAttrs(ultimate);
101                   result.AcquireLEN(ultimate);
102                   return std::move(result.Rewrite(context));
103                 }
104               }
105             }
106             return std::nullopt;
107           },
108       },
109       // GetUltimate() used here, not ResolveAssociations(), because
110       // we need the type/rank of an associate entity from TYPE IS,
111       // CLASS IS, or RANK statement.
112       ultimate.details());
113 }
114 
115 std::optional<TypeAndShape> TypeAndShape::Characterize(
116     const semantics::AssocEntityDetails &assoc, FoldingContext &context) {
117   std::optional<TypeAndShape> result;
118   if (auto type{DynamicType::From(assoc.type())}) {
119     if (auto rank{assoc.rank()}) {
120       if (*rank >= 0 && *rank <= common::maxRank) {
121         result = TypeAndShape{std::move(*type), Shape(*rank)};
122       }
123     } else if (auto shape{GetShape(context, assoc.expr())}) {
124       result = TypeAndShape{std::move(*type), std::move(*shape)};
125     }
126     if (result && type->category() == TypeCategory::Character) {
127       if (const auto *chExpr{UnwrapExpr<Expr<SomeCharacter>>(assoc.expr())}) {
128         if (auto len{chExpr->LEN()}) {
129           result->set_LEN(std::move(*len));
130         }
131       }
132     }
133   }
134   return Fold(context, std::move(result));
135 }
136 
137 std::optional<TypeAndShape> TypeAndShape::Characterize(
138     const semantics::DeclTypeSpec &spec, FoldingContext &context) {
139   if (auto type{DynamicType::From(spec)}) {
140     return Fold(context, TypeAndShape{std::move(*type)});
141   } else {
142     return std::nullopt;
143   }
144 }
145 
146 std::optional<TypeAndShape> TypeAndShape::Characterize(
147     const ActualArgument &arg, FoldingContext &context) {
148   return Characterize(arg.UnwrapExpr(), context);
149 }
150 
151 bool TypeAndShape::IsCompatibleWith(parser::ContextualMessages &messages,
152     const TypeAndShape &that, const char *thisIs, const char *thatIs,
153     bool omitShapeConformanceCheck,
154     enum CheckConformanceFlags::Flags flags) const {
155   if (!type_.IsTkCompatibleWith(that.type_)) {
156     messages.Say(
157         "%1$s type '%2$s' is not compatible with %3$s type '%4$s'"_err_en_US,
158         thatIs, that.AsFortran(), thisIs, AsFortran());
159     return false;
160   }
161   return omitShapeConformanceCheck ||
162       CheckConformance(messages, shape_, that.shape_, flags, thisIs, thatIs)
163           .value_or(true /*fail only when nonconformance is known now*/);
164 }
165 
166 std::optional<Expr<SubscriptInteger>> TypeAndShape::MeasureElementSizeInBytes(
167     FoldingContext &foldingContext, bool align) const {
168   if (LEN_) {
169     CHECK(type_.category() == TypeCategory::Character);
170     return Fold(foldingContext,
171         Expr<SubscriptInteger>{
172             foldingContext.targetCharacteristics().GetByteSize(
173                 type_.category(), type_.kind())} *
174             Expr<SubscriptInteger>{*LEN_});
175   }
176   if (auto elementBytes{type_.MeasureSizeInBytes(foldingContext, align)}) {
177     return Fold(foldingContext, std::move(*elementBytes));
178   }
179   return std::nullopt;
180 }
181 
182 std::optional<Expr<SubscriptInteger>> TypeAndShape::MeasureSizeInBytes(
183     FoldingContext &foldingContext) const {
184   if (auto elements{GetSize(Shape{shape_})}) {
185     // Sizes of arrays (even with single elements) are multiples of
186     // their alignments.
187     if (auto elementBytes{
188             MeasureElementSizeInBytes(foldingContext, GetRank(shape_) > 0)}) {
189       return Fold(
190           foldingContext, std::move(*elements) * std::move(*elementBytes));
191     }
192   }
193   return std::nullopt;
194 }
195 
196 void TypeAndShape::AcquireAttrs(const semantics::Symbol &symbol) {
197   if (IsAssumedShape(symbol)) {
198     attrs_.set(Attr::AssumedShape);
199   }
200   if (IsDeferredShape(symbol)) {
201     attrs_.set(Attr::DeferredShape);
202   }
203   if (const auto *object{
204           symbol.GetUltimate().detailsIf<semantics::ObjectEntityDetails>()}) {
205     corank_ = object->coshape().Rank();
206     if (object->IsAssumedRank()) {
207       attrs_.set(Attr::AssumedRank);
208     }
209     if (object->IsAssumedSize()) {
210       attrs_.set(Attr::AssumedSize);
211     }
212     if (object->IsCoarray()) {
213       attrs_.set(Attr::Coarray);
214     }
215   }
216 }
217 
218 void TypeAndShape::AcquireLEN() {
219   if (auto len{type_.GetCharLength()}) {
220     LEN_ = std::move(len);
221   }
222 }
223 
224 void TypeAndShape::AcquireLEN(const semantics::Symbol &symbol) {
225   if (type_.category() == TypeCategory::Character) {
226     if (auto len{DataRef{symbol}.LEN()}) {
227       LEN_ = std::move(*len);
228     }
229   }
230 }
231 
232 std::string TypeAndShape::AsFortran() const {
233   return type_.AsFortran(LEN_ ? LEN_->AsFortran() : "");
234 }
235 
236 llvm::raw_ostream &TypeAndShape::Dump(llvm::raw_ostream &o) const {
237   o << type_.AsFortran(LEN_ ? LEN_->AsFortran() : "");
238   attrs_.Dump(o, EnumToString);
239   if (!shape_.empty()) {
240     o << " dimension";
241     char sep{'('};
242     for (const auto &expr : shape_) {
243       o << sep;
244       sep = ',';
245       if (expr) {
246         expr->AsFortran(o);
247       } else {
248         o << ':';
249       }
250     }
251     o << ')';
252   }
253   return o;
254 }
255 
256 bool DummyDataObject::operator==(const DummyDataObject &that) const {
257   return type == that.type && attrs == that.attrs && intent == that.intent &&
258       coshape == that.coshape;
259 }
260 
261 static bool AreCompatibleDummyDataObjectShapes(const Shape &x, const Shape &y) {
262   // TODO: Validate more than just compatible ranks
263   return GetRank(x) == GetRank(y);
264 }
265 
266 bool DummyDataObject::IsCompatibleWith(
267     const DummyDataObject &actual, std::string *whyNot) const {
268   if (!AreCompatibleDummyDataObjectShapes(type.shape(), actual.type.shape())) {
269     if (whyNot) {
270       *whyNot = "incompatible dummy data object shapes";
271     }
272     return false;
273   }
274   if (!type.type().IsTkCompatibleWith(actual.type.type())) {
275     if (whyNot) {
276       *whyNot = "incompatible dummy data object types: "s +
277           type.type().AsFortran() + " vs " + actual.type.type().AsFortran();
278     }
279     return false;
280   }
281   if (attrs != actual.attrs) {
282     if (whyNot) {
283       *whyNot = "incompatible dummy data object attributes";
284     }
285     return false;
286   }
287   if (intent != actual.intent) {
288     if (whyNot) {
289       *whyNot = "incompatible dummy data object intents";
290     }
291     return false;
292   }
293   if (coshape != actual.coshape) {
294     if (whyNot) {
295       *whyNot = "incompatible dummy data object coshapes";
296     }
297     return false;
298   }
299   return true;
300 }
301 
302 static common::Intent GetIntent(const semantics::Attrs &attrs) {
303   if (attrs.test(semantics::Attr::INTENT_IN)) {
304     return common::Intent::In;
305   } else if (attrs.test(semantics::Attr::INTENT_OUT)) {
306     return common::Intent::Out;
307   } else if (attrs.test(semantics::Attr::INTENT_INOUT)) {
308     return common::Intent::InOut;
309   } else {
310     return common::Intent::Default;
311   }
312 }
313 
314 std::optional<DummyDataObject> DummyDataObject::Characterize(
315     const semantics::Symbol &symbol, FoldingContext &context) {
316   if (symbol.has<semantics::ObjectEntityDetails>() ||
317       symbol.has<semantics::EntityDetails>()) {
318     if (auto type{TypeAndShape::Characterize(symbol, context)}) {
319       std::optional<DummyDataObject> result{std::move(*type)};
320       using semantics::Attr;
321       CopyAttrs<DummyDataObject, DummyDataObject::Attr>(symbol, *result,
322           {
323               {Attr::OPTIONAL, DummyDataObject::Attr::Optional},
324               {Attr::ALLOCATABLE, DummyDataObject::Attr::Allocatable},
325               {Attr::ASYNCHRONOUS, DummyDataObject::Attr::Asynchronous},
326               {Attr::CONTIGUOUS, DummyDataObject::Attr::Contiguous},
327               {Attr::VALUE, DummyDataObject::Attr::Value},
328               {Attr::VOLATILE, DummyDataObject::Attr::Volatile},
329               {Attr::POINTER, DummyDataObject::Attr::Pointer},
330               {Attr::TARGET, DummyDataObject::Attr::Target},
331           });
332       result->intent = GetIntent(symbol.attrs());
333       return result;
334     }
335   }
336   return std::nullopt;
337 }
338 
339 bool DummyDataObject::CanBePassedViaImplicitInterface() const {
340   if ((attrs &
341           Attrs{Attr::Allocatable, Attr::Asynchronous, Attr::Optional,
342               Attr::Pointer, Attr::Target, Attr::Value, Attr::Volatile})
343           .any()) {
344     return false; // 15.4.2.2(3)(a)
345   } else if ((type.attrs() &
346                  TypeAndShape::Attrs{TypeAndShape::Attr::AssumedShape,
347                      TypeAndShape::Attr::AssumedRank,
348                      TypeAndShape::Attr::Coarray})
349                  .any()) {
350     return false; // 15.4.2.2(3)(b-d)
351   } else if (type.type().IsPolymorphic()) {
352     return false; // 15.4.2.2(3)(f)
353   } else if (const auto *derived{GetDerivedTypeSpec(type.type())}) {
354     return derived->parameters().empty(); // 15.4.2.2(3)(e)
355   } else {
356     return true;
357   }
358 }
359 
360 llvm::raw_ostream &DummyDataObject::Dump(llvm::raw_ostream &o) const {
361   attrs.Dump(o, EnumToString);
362   if (intent != common::Intent::Default) {
363     o << "INTENT(" << common::EnumToString(intent) << ')';
364   }
365   type.Dump(o);
366   if (!coshape.empty()) {
367     char sep{'['};
368     for (const auto &expr : coshape) {
369       expr.AsFortran(o << sep);
370       sep = ',';
371     }
372   }
373   return o;
374 }
375 
376 DummyProcedure::DummyProcedure(Procedure &&p)
377     : procedure{new Procedure{std::move(p)}} {}
378 
379 bool DummyProcedure::operator==(const DummyProcedure &that) const {
380   return attrs == that.attrs && intent == that.intent &&
381       procedure.value() == that.procedure.value();
382 }
383 
384 bool DummyProcedure::IsCompatibleWith(
385     const DummyProcedure &actual, std::string *whyNot) const {
386   if (attrs != actual.attrs) {
387     if (whyNot) {
388       *whyNot = "incompatible dummy procedure attributes";
389     }
390     return false;
391   }
392   if (intent != actual.intent) {
393     if (whyNot) {
394       *whyNot = "incompatible dummy procedure intents";
395     }
396     return false;
397   }
398   if (!procedure.value().IsCompatibleWith(actual.procedure.value(), whyNot)) {
399     if (whyNot) {
400       *whyNot = "incompatible dummy procedure interfaces: "s + *whyNot;
401     }
402     return false;
403   }
404   return true;
405 }
406 
407 static std::string GetSeenProcs(
408     const semantics::UnorderedSymbolSet &seenProcs) {
409   // Sort the symbols so that they appear in the same order on all platforms
410   auto ordered{semantics::OrderBySourcePosition(seenProcs)};
411   std::string result;
412   llvm::interleave(
413       ordered,
414       [&](const SymbolRef p) { result += '\'' + p->name().ToString() + '\''; },
415       [&]() { result += ", "; });
416   return result;
417 }
418 
419 // These functions with arguments of type UnorderedSymbolSet are used with
420 // mutually recursive calls when characterizing a Procedure, a DummyArgument,
421 // or a DummyProcedure to detect circularly defined procedures as required by
422 // 15.4.3.6, paragraph 2.
423 static std::optional<DummyArgument> CharacterizeDummyArgument(
424     const semantics::Symbol &symbol, FoldingContext &context,
425     semantics::UnorderedSymbolSet seenProcs);
426 static std::optional<FunctionResult> CharacterizeFunctionResult(
427     const semantics::Symbol &symbol, FoldingContext &context,
428     semantics::UnorderedSymbolSet seenProcs);
429 
430 static std::optional<Procedure> CharacterizeProcedure(
431     const semantics::Symbol &original, FoldingContext &context,
432     semantics::UnorderedSymbolSet seenProcs) {
433   Procedure result;
434   const auto &symbol{ResolveAssociations(original)};
435   if (seenProcs.find(symbol) != seenProcs.end()) {
436     std::string procsList{GetSeenProcs(seenProcs)};
437     context.messages().Say(symbol.name(),
438         "Procedure '%s' is recursively defined.  Procedures in the cycle:"
439         " %s"_err_en_US,
440         symbol.name(), procsList);
441     return std::nullopt;
442   }
443   seenProcs.insert(symbol);
444   if (IsElementalProcedure(symbol)) {
445     result.attrs.set(Procedure::Attr::Elemental);
446   }
447   CopyAttrs<Procedure, Procedure::Attr>(symbol, result,
448       {
449           {semantics::Attr::BIND_C, Procedure::Attr::BindC},
450       });
451   if (IsPureProcedure(symbol) || // works for ENTRY too
452       (!symbol.attrs().test(semantics::Attr::IMPURE) &&
453           result.attrs.test(Procedure::Attr::Elemental))) {
454     result.attrs.set(Procedure::Attr::Pure);
455   }
456   return common::visit(
457       common::visitors{
458           [&](const semantics::SubprogramDetails &subp)
459               -> std::optional<Procedure> {
460             if (subp.isFunction()) {
461               if (auto fr{CharacterizeFunctionResult(
462                       subp.result(), context, seenProcs)}) {
463                 result.functionResult = std::move(fr);
464               } else {
465                 return std::nullopt;
466               }
467             } else {
468               result.attrs.set(Procedure::Attr::Subroutine);
469             }
470             for (const semantics::Symbol *arg : subp.dummyArgs()) {
471               if (!arg) {
472                 if (subp.isFunction()) {
473                   return std::nullopt;
474                 } else {
475                   result.dummyArguments.emplace_back(AlternateReturn{});
476                 }
477               } else if (auto argCharacteristics{CharacterizeDummyArgument(
478                              *arg, context, seenProcs)}) {
479                 result.dummyArguments.emplace_back(
480                     std::move(argCharacteristics.value()));
481               } else {
482                 return std::nullopt;
483               }
484             }
485             return result;
486           },
487           [&](const semantics::ProcEntityDetails &proc)
488               -> std::optional<Procedure> {
489             if (symbol.attrs().test(semantics::Attr::INTRINSIC)) {
490               // Fails when the intrinsic is not a specific intrinsic function
491               // from F'2018 table 16.2.  In order to handle forward references,
492               // attempts to use impermissible intrinsic procedures as the
493               // interfaces of procedure pointers are caught and flagged in
494               // declaration checking in Semantics.
495               auto intrinsic{context.intrinsics().IsSpecificIntrinsicFunction(
496                   symbol.name().ToString())};
497               if (intrinsic && intrinsic->isRestrictedSpecific) {
498                 intrinsic.reset(); // Exclude intrinsics from table 16.3.
499               }
500               return intrinsic;
501             }
502             const semantics::ProcInterface &interface { proc.interface() };
503             if (const semantics::Symbol * interfaceSymbol{interface.symbol()}) {
504               auto interface {
505                 CharacterizeProcedure(*interfaceSymbol, context, seenProcs)
506               };
507               if (interface && IsPointer(symbol)) {
508                 interface->attrs.reset(Procedure::Attr::Elemental);
509               }
510               return interface;
511             } else {
512               result.attrs.set(Procedure::Attr::ImplicitInterface);
513               const semantics::DeclTypeSpec *type{interface.type()};
514               if (symbol.test(semantics::Symbol::Flag::Subroutine)) {
515                 // ignore any implicit typing
516                 result.attrs.set(Procedure::Attr::Subroutine);
517               } else if (type) {
518                 if (auto resultType{DynamicType::From(*type)}) {
519                   result.functionResult = FunctionResult{*resultType};
520                 } else {
521                   return std::nullopt;
522                 }
523               } else if (symbol.test(semantics::Symbol::Flag::Function)) {
524                 return std::nullopt;
525               }
526               // The PASS name, if any, is not a characteristic.
527               return result;
528             }
529           },
530           [&](const semantics::ProcBindingDetails &binding) {
531             if (auto result{CharacterizeProcedure(
532                     binding.symbol(), context, seenProcs)}) {
533               if (!symbol.attrs().test(semantics::Attr::NOPASS)) {
534                 auto passName{binding.passName()};
535                 for (auto &dummy : result->dummyArguments) {
536                   if (!passName || dummy.name.c_str() == *passName) {
537                     dummy.pass = true;
538                     return result;
539                   }
540                 }
541                 DIE("PASS argument missing");
542               }
543               return result;
544             } else {
545               return std::optional<Procedure>{};
546             }
547           },
548           [&](const semantics::UseDetails &use) {
549             return CharacterizeProcedure(use.symbol(), context, seenProcs);
550           },
551           [](const semantics::UseErrorDetails &) {
552             // Ambiguous use-association will be handled later during symbol
553             // checks, ignore UseErrorDetails here without actual symbol usage.
554             return std::optional<Procedure>{};
555           },
556           [&](const semantics::HostAssocDetails &assoc) {
557             return CharacterizeProcedure(assoc.symbol(), context, seenProcs);
558           },
559           [&](const semantics::EntityDetails &) {
560             context.messages().Say(
561                 "Procedure '%s' is referenced before being sufficiently defined in a context where it must be so"_err_en_US,
562                 symbol.name());
563             return std::optional<Procedure>{};
564           },
565           [&](const semantics::SubprogramNameDetails &) {
566             context.messages().Say(
567                 "Procedure '%s' is referenced before being sufficiently defined in a context where it must be so"_err_en_US,
568                 symbol.name());
569             return std::optional<Procedure>{};
570           },
571           [&](const auto &) {
572             context.messages().Say(
573                 "'%s' is not a procedure"_err_en_US, symbol.name());
574             return std::optional<Procedure>{};
575           },
576       },
577       symbol.details());
578 }
579 
580 static std::optional<DummyProcedure> CharacterizeDummyProcedure(
581     const semantics::Symbol &symbol, FoldingContext &context,
582     semantics::UnorderedSymbolSet seenProcs) {
583   if (auto procedure{CharacterizeProcedure(symbol, context, seenProcs)}) {
584     // Dummy procedures may not be elemental.  Elemental dummy procedure
585     // interfaces are errors when the interface is not intrinsic, and that
586     // error is caught elsewhere.  Elemental intrinsic interfaces are
587     // made non-elemental.
588     procedure->attrs.reset(Procedure::Attr::Elemental);
589     DummyProcedure result{std::move(procedure.value())};
590     CopyAttrs<DummyProcedure, DummyProcedure::Attr>(symbol, result,
591         {
592             {semantics::Attr::OPTIONAL, DummyProcedure::Attr::Optional},
593             {semantics::Attr::POINTER, DummyProcedure::Attr::Pointer},
594         });
595     result.intent = GetIntent(symbol.attrs());
596     return result;
597   } else {
598     return std::nullopt;
599   }
600 }
601 
602 llvm::raw_ostream &DummyProcedure::Dump(llvm::raw_ostream &o) const {
603   attrs.Dump(o, EnumToString);
604   if (intent != common::Intent::Default) {
605     o << "INTENT(" << common::EnumToString(intent) << ')';
606   }
607   procedure.value().Dump(o);
608   return o;
609 }
610 
611 llvm::raw_ostream &AlternateReturn::Dump(llvm::raw_ostream &o) const {
612   return o << '*';
613 }
614 
615 DummyArgument::~DummyArgument() {}
616 
617 bool DummyArgument::operator==(const DummyArgument &that) const {
618   return u == that.u; // name and passed-object usage are not characteristics
619 }
620 
621 bool DummyArgument::IsCompatibleWith(
622     const DummyArgument &actual, std::string *whyNot) const {
623   if (const auto *ifaceData{std::get_if<DummyDataObject>(&u)}) {
624     if (const auto *actualData{std::get_if<DummyDataObject>(&actual.u)}) {
625       return ifaceData->IsCompatibleWith(*actualData, whyNot);
626     }
627     if (whyNot) {
628       *whyNot = "one dummy argument is an object, the other is not";
629     }
630   } else if (const auto *ifaceProc{std::get_if<DummyProcedure>(&u)}) {
631     if (const auto *actualProc{std::get_if<DummyProcedure>(&actual.u)}) {
632       return ifaceProc->IsCompatibleWith(*actualProc, whyNot);
633     }
634     if (whyNot) {
635       *whyNot = "one dummy argument is a procedure, the other is not";
636     }
637   } else {
638     CHECK(std::holds_alternative<AlternateReturn>(u));
639     if (std::holds_alternative<AlternateReturn>(actual.u)) {
640       return true;
641     }
642     if (whyNot) {
643       *whyNot = "one dummy argument is an alternate return, the other is not";
644     }
645   }
646   return false;
647 }
648 
649 static std::optional<DummyArgument> CharacterizeDummyArgument(
650     const semantics::Symbol &symbol, FoldingContext &context,
651     semantics::UnorderedSymbolSet seenProcs) {
652   auto name{symbol.name().ToString()};
653   if (symbol.has<semantics::ObjectEntityDetails>() ||
654       symbol.has<semantics::EntityDetails>()) {
655     if (auto obj{DummyDataObject::Characterize(symbol, context)}) {
656       return DummyArgument{std::move(name), std::move(obj.value())};
657     }
658   } else if (auto proc{
659                  CharacterizeDummyProcedure(symbol, context, seenProcs)}) {
660     return DummyArgument{std::move(name), std::move(proc.value())};
661   }
662   return std::nullopt;
663 }
664 
665 std::optional<DummyArgument> DummyArgument::FromActual(
666     std::string &&name, const Expr<SomeType> &expr, FoldingContext &context) {
667   return common::visit(
668       common::visitors{
669           [&](const BOZLiteralConstant &) {
670             return std::make_optional<DummyArgument>(std::move(name),
671                 DummyDataObject{
672                     TypeAndShape{DynamicType::TypelessIntrinsicArgument()}});
673           },
674           [&](const NullPointer &) {
675             return std::make_optional<DummyArgument>(std::move(name),
676                 DummyDataObject{
677                     TypeAndShape{DynamicType::TypelessIntrinsicArgument()}});
678           },
679           [&](const ProcedureDesignator &designator) {
680             if (auto proc{Procedure::Characterize(designator, context)}) {
681               return std::make_optional<DummyArgument>(
682                   std::move(name), DummyProcedure{std::move(*proc)});
683             } else {
684               return std::optional<DummyArgument>{};
685             }
686           },
687           [&](const ProcedureRef &call) {
688             if (auto proc{Procedure::Characterize(call, context)}) {
689               return std::make_optional<DummyArgument>(
690                   std::move(name), DummyProcedure{std::move(*proc)});
691             } else {
692               return std::optional<DummyArgument>{};
693             }
694           },
695           [&](const auto &) {
696             if (auto type{TypeAndShape::Characterize(expr, context)}) {
697               return std::make_optional<DummyArgument>(
698                   std::move(name), DummyDataObject{std::move(*type)});
699             } else {
700               return std::optional<DummyArgument>{};
701             }
702           },
703       },
704       expr.u);
705 }
706 
707 bool DummyArgument::IsOptional() const {
708   return common::visit(
709       common::visitors{
710           [](const DummyDataObject &data) {
711             return data.attrs.test(DummyDataObject::Attr::Optional);
712           },
713           [](const DummyProcedure &proc) {
714             return proc.attrs.test(DummyProcedure::Attr::Optional);
715           },
716           [](const AlternateReturn &) { return false; },
717       },
718       u);
719 }
720 
721 void DummyArgument::SetOptional(bool value) {
722   common::visit(common::visitors{
723                     [value](DummyDataObject &data) {
724                       data.attrs.set(DummyDataObject::Attr::Optional, value);
725                     },
726                     [value](DummyProcedure &proc) {
727                       proc.attrs.set(DummyProcedure::Attr::Optional, value);
728                     },
729                     [](AlternateReturn &) { DIE("cannot set optional"); },
730                 },
731       u);
732 }
733 
734 void DummyArgument::SetIntent(common::Intent intent) {
735   common::visit(common::visitors{
736                     [intent](DummyDataObject &data) { data.intent = intent; },
737                     [intent](DummyProcedure &proc) { proc.intent = intent; },
738                     [](AlternateReturn &) { DIE("cannot set intent"); },
739                 },
740       u);
741 }
742 
743 common::Intent DummyArgument::GetIntent() const {
744   return common::visit(
745       common::visitors{
746           [](const DummyDataObject &data) { return data.intent; },
747           [](const DummyProcedure &proc) { return proc.intent; },
748           [](const AlternateReturn &) -> common::Intent {
749             DIE("Alternate returns have no intent");
750           },
751       },
752       u);
753 }
754 
755 bool DummyArgument::CanBePassedViaImplicitInterface() const {
756   if (const auto *object{std::get_if<DummyDataObject>(&u)}) {
757     return object->CanBePassedViaImplicitInterface();
758   } else {
759     return true;
760   }
761 }
762 
763 bool DummyArgument::IsTypelessIntrinsicDummy() const {
764   const auto *argObj{std::get_if<characteristics::DummyDataObject>(&u)};
765   return argObj && argObj->type.type().IsTypelessIntrinsicArgument();
766 }
767 
768 llvm::raw_ostream &DummyArgument::Dump(llvm::raw_ostream &o) const {
769   if (!name.empty()) {
770     o << name << '=';
771   }
772   if (pass) {
773     o << " PASS";
774   }
775   common::visit([&](const auto &x) { x.Dump(o); }, u);
776   return o;
777 }
778 
779 FunctionResult::FunctionResult(DynamicType t) : u{TypeAndShape{t}} {}
780 FunctionResult::FunctionResult(TypeAndShape &&t) : u{std::move(t)} {}
781 FunctionResult::FunctionResult(Procedure &&p) : u{std::move(p)} {}
782 FunctionResult::~FunctionResult() {}
783 
784 bool FunctionResult::operator==(const FunctionResult &that) const {
785   return attrs == that.attrs && u == that.u;
786 }
787 
788 static std::optional<FunctionResult> CharacterizeFunctionResult(
789     const semantics::Symbol &symbol, FoldingContext &context,
790     semantics::UnorderedSymbolSet seenProcs) {
791   if (symbol.has<semantics::ObjectEntityDetails>()) {
792     if (auto type{TypeAndShape::Characterize(symbol, context)}) {
793       FunctionResult result{std::move(*type)};
794       CopyAttrs<FunctionResult, FunctionResult::Attr>(symbol, result,
795           {
796               {semantics::Attr::ALLOCATABLE, FunctionResult::Attr::Allocatable},
797               {semantics::Attr::CONTIGUOUS, FunctionResult::Attr::Contiguous},
798               {semantics::Attr::POINTER, FunctionResult::Attr::Pointer},
799           });
800       return result;
801     }
802   } else if (auto maybeProc{
803                  CharacterizeProcedure(symbol, context, seenProcs)}) {
804     FunctionResult result{std::move(*maybeProc)};
805     result.attrs.set(FunctionResult::Attr::Pointer);
806     return result;
807   }
808   return std::nullopt;
809 }
810 
811 std::optional<FunctionResult> FunctionResult::Characterize(
812     const Symbol &symbol, FoldingContext &context) {
813   semantics::UnorderedSymbolSet seenProcs;
814   return CharacterizeFunctionResult(symbol, context, seenProcs);
815 }
816 
817 bool FunctionResult::IsAssumedLengthCharacter() const {
818   if (const auto *ts{std::get_if<TypeAndShape>(&u)}) {
819     return ts->type().IsAssumedLengthCharacter();
820   } else {
821     return false;
822   }
823 }
824 
825 bool FunctionResult::CanBeReturnedViaImplicitInterface() const {
826   if (attrs.test(Attr::Pointer) || attrs.test(Attr::Allocatable)) {
827     return false; // 15.4.2.2(4)(b)
828   } else if (const auto *typeAndShape{GetTypeAndShape()}) {
829     if (typeAndShape->Rank() > 0) {
830       return false; // 15.4.2.2(4)(a)
831     } else {
832       const DynamicType &type{typeAndShape->type()};
833       switch (type.category()) {
834       case TypeCategory::Character:
835         if (type.knownLength()) {
836           return true;
837         } else if (const auto *param{type.charLengthParamValue()}) {
838           if (const auto &expr{param->GetExplicit()}) {
839             return IsConstantExpr(*expr); // 15.4.2.2(4)(c)
840           } else if (param->isAssumed()) {
841             return true;
842           }
843         }
844         return false;
845       case TypeCategory::Derived:
846         if (!type.IsPolymorphic()) {
847           const auto &spec{type.GetDerivedTypeSpec()};
848           for (const auto &pair : spec.parameters()) {
849             if (const auto &expr{pair.second.GetExplicit()}) {
850               if (!IsConstantExpr(*expr)) {
851                 return false; // 15.4.2.2(4)(c)
852               }
853             }
854           }
855           return true;
856         }
857         return false;
858       default:
859         return true;
860       }
861     }
862   } else {
863     return false; // 15.4.2.2(4)(b) - procedure pointer
864   }
865 }
866 
867 bool FunctionResult::IsCompatibleWith(
868     const FunctionResult &actual, std::string *whyNot) const {
869   Attrs actualAttrs{actual.attrs};
870   if (!attrs.test(Attr::Contiguous)) {
871     actualAttrs.reset(Attr::Contiguous);
872   }
873   if (attrs != actualAttrs) {
874     if (whyNot) {
875       *whyNot = "function results have incompatible attributes";
876     }
877   } else if (const auto *ifaceTypeShape{std::get_if<TypeAndShape>(&u)}) {
878     if (const auto *actualTypeShape{std::get_if<TypeAndShape>(&actual.u)}) {
879       if (ifaceTypeShape->Rank() != actualTypeShape->Rank()) {
880         if (whyNot) {
881           *whyNot = "function results have distinct ranks";
882         }
883       } else if (!attrs.test(Attr::Allocatable) && !attrs.test(Attr::Pointer) &&
884           ifaceTypeShape->shape() != actualTypeShape->shape()) {
885         if (whyNot) {
886           *whyNot = "function results have distinct extents";
887         }
888       } else if (!ifaceTypeShape->type().IsTkCompatibleWith(
889                      actualTypeShape->type())) {
890         if (whyNot) {
891           *whyNot = "function results have incompatible types: "s +
892               ifaceTypeShape->type().AsFortran() + " vs "s +
893               actualTypeShape->type().AsFortran();
894         }
895       } else {
896         return true;
897       }
898     } else {
899       if (whyNot) {
900         *whyNot = "function result type and shape are not known";
901       }
902     }
903   } else {
904     const auto *ifaceProc{std::get_if<CopyableIndirection<Procedure>>(&u)};
905     CHECK(ifaceProc != nullptr);
906     if (const auto *actualProc{
907             std::get_if<CopyableIndirection<Procedure>>(&actual.u)}) {
908       if (ifaceProc->value().IsCompatibleWith(actualProc->value(), whyNot)) {
909         return true;
910       }
911       if (whyNot) {
912         *whyNot =
913             "function results are incompatible procedure pointers: "s + *whyNot;
914       }
915     } else {
916       if (whyNot) {
917         *whyNot =
918             "one function result is a procedure pointer, the other is not";
919       }
920     }
921   }
922   return false;
923 }
924 
925 llvm::raw_ostream &FunctionResult::Dump(llvm::raw_ostream &o) const {
926   attrs.Dump(o, EnumToString);
927   common::visit(common::visitors{
928                     [&](const TypeAndShape &ts) { ts.Dump(o); },
929                     [&](const CopyableIndirection<Procedure> &p) {
930                       p.value().Dump(o << " procedure(") << ')';
931                     },
932                 },
933       u);
934   return o;
935 }
936 
937 Procedure::Procedure(FunctionResult &&fr, DummyArguments &&args, Attrs a)
938     : functionResult{std::move(fr)}, dummyArguments{std::move(args)}, attrs{a} {
939 }
940 Procedure::Procedure(DummyArguments &&args, Attrs a)
941     : dummyArguments{std::move(args)}, attrs{a} {}
942 Procedure::~Procedure() {}
943 
944 bool Procedure::operator==(const Procedure &that) const {
945   return attrs == that.attrs && functionResult == that.functionResult &&
946       dummyArguments == that.dummyArguments;
947 }
948 
949 bool Procedure::IsCompatibleWith(const Procedure &actual, std::string *whyNot,
950     const SpecificIntrinsic *specificIntrinsic) const {
951   // 15.5.2.9(1): if dummy is not pure, actual need not be.
952   // Ditto with elemental.
953   Attrs actualAttrs{actual.attrs};
954   if (!attrs.test(Attr::Pure)) {
955     actualAttrs.reset(Attr::Pure);
956   }
957   if (!attrs.test(Attr::Elemental) && specificIntrinsic) {
958     actualAttrs.reset(Attr::Elemental);
959   }
960   Attrs differences{attrs ^ actualAttrs};
961   differences.reset(Attr::Subroutine); // dealt with specifically later
962   if (!differences.empty()) {
963     if (whyNot) {
964       auto sep{": "s};
965       *whyNot = "incompatible procedure attributes";
966       differences.IterateOverMembers([&](Attr x) {
967         *whyNot += sep + EnumToString(x);
968         sep = ", ";
969       });
970     }
971   } else if ((IsFunction() && actual.IsSubroutine()) ||
972       (IsSubroutine() && actual.IsFunction())) {
973     if (whyNot) {
974       *whyNot =
975           "incompatible procedures: one is a function, the other a subroutine";
976     }
977   } else if (functionResult && actual.functionResult &&
978       !functionResult->IsCompatibleWith(*actual.functionResult, whyNot)) {
979   } else if (dummyArguments.size() != actual.dummyArguments.size()) {
980     if (whyNot) {
981       *whyNot = "distinct numbers of dummy arguments";
982     }
983   } else {
984     for (std::size_t j{0}; j < dummyArguments.size(); ++j) {
985       if (!dummyArguments[j].IsCompatibleWith(
986               actual.dummyArguments[j], whyNot)) {
987         if (whyNot) {
988           *whyNot = "incompatible dummy argument #"s + std::to_string(j + 1) +
989               ": "s + *whyNot;
990         }
991         return false;
992       }
993     }
994     return true;
995   }
996   return false;
997 }
998 
999 int Procedure::FindPassIndex(std::optional<parser::CharBlock> name) const {
1000   int argCount{static_cast<int>(dummyArguments.size())};
1001   int index{0};
1002   if (name) {
1003     while (index < argCount && *name != dummyArguments[index].name.c_str()) {
1004       ++index;
1005     }
1006   }
1007   CHECK(index < argCount);
1008   return index;
1009 }
1010 
1011 bool Procedure::CanOverride(
1012     const Procedure &that, std::optional<int> passIndex) const {
1013   // A pure procedure may override an impure one (7.5.7.3(2))
1014   if ((that.attrs.test(Attr::Pure) && !attrs.test(Attr::Pure)) ||
1015       that.attrs.test(Attr::Elemental) != attrs.test(Attr::Elemental) ||
1016       functionResult != that.functionResult) {
1017     return false;
1018   }
1019   int argCount{static_cast<int>(dummyArguments.size())};
1020   if (argCount != static_cast<int>(that.dummyArguments.size())) {
1021     return false;
1022   }
1023   for (int j{0}; j < argCount; ++j) {
1024     if ((!passIndex || j != *passIndex) &&
1025         dummyArguments[j] != that.dummyArguments[j]) {
1026       return false;
1027     }
1028   }
1029   return true;
1030 }
1031 
1032 std::optional<Procedure> Procedure::Characterize(
1033     const semantics::Symbol &original, FoldingContext &context) {
1034   semantics::UnorderedSymbolSet seenProcs;
1035   return CharacterizeProcedure(original, context, seenProcs);
1036 }
1037 
1038 std::optional<Procedure> Procedure::Characterize(
1039     const ProcedureDesignator &proc, FoldingContext &context) {
1040   if (const auto *symbol{proc.GetSymbol()}) {
1041     if (auto result{
1042             characteristics::Procedure::Characterize(*symbol, context)}) {
1043       return result;
1044     }
1045   } else if (const auto *intrinsic{proc.GetSpecificIntrinsic()}) {
1046     return intrinsic->characteristics.value();
1047   }
1048   return std::nullopt;
1049 }
1050 
1051 std::optional<Procedure> Procedure::Characterize(
1052     const ProcedureRef &ref, FoldingContext &context) {
1053   if (auto callee{Characterize(ref.proc(), context)}) {
1054     if (callee->functionResult) {
1055       if (const Procedure *
1056           proc{callee->functionResult->IsProcedurePointer()}) {
1057         return {*proc};
1058       }
1059     }
1060   }
1061   return std::nullopt;
1062 }
1063 
1064 bool Procedure::CanBeCalledViaImplicitInterface() const {
1065   // TODO: Pass back information on why we return false
1066   if (attrs.test(Attr::Elemental) || attrs.test(Attr::BindC)) {
1067     return false; // 15.4.2.2(5,6)
1068   } else if (IsFunction() &&
1069       !functionResult->CanBeReturnedViaImplicitInterface()) {
1070     return false;
1071   } else {
1072     for (const DummyArgument &arg : dummyArguments) {
1073       if (!arg.CanBePassedViaImplicitInterface()) {
1074         return false;
1075       }
1076     }
1077     return true;
1078   }
1079 }
1080 
1081 llvm::raw_ostream &Procedure::Dump(llvm::raw_ostream &o) const {
1082   attrs.Dump(o, EnumToString);
1083   if (functionResult) {
1084     functionResult->Dump(o << "TYPE(") << ") FUNCTION";
1085   } else if (attrs.test(Attr::Subroutine)) {
1086     o << "SUBROUTINE";
1087   } else {
1088     o << "EXTERNAL";
1089   }
1090   char sep{'('};
1091   for (const auto &dummy : dummyArguments) {
1092     dummy.Dump(o << sep);
1093     sep = ',';
1094   }
1095   return o << (sep == '(' ? "()" : ")");
1096 }
1097 
1098 // Utility class to determine if Procedures, etc. are distinguishable
1099 class DistinguishUtils {
1100 public:
1101   explicit DistinguishUtils(const common::LanguageFeatureControl &features)
1102       : features_{features} {}
1103 
1104   // Are these procedures distinguishable for a generic name?
1105   bool Distinguishable(const Procedure &, const Procedure &) const;
1106   // Are these procedures distinguishable for a generic operator or assignment?
1107   bool DistinguishableOpOrAssign(const Procedure &, const Procedure &) const;
1108 
1109 private:
1110   struct CountDummyProcedures {
1111     CountDummyProcedures(const DummyArguments &args) {
1112       for (const DummyArgument &arg : args) {
1113         if (std::holds_alternative<DummyProcedure>(arg.u)) {
1114           total += 1;
1115           notOptional += !arg.IsOptional();
1116         }
1117       }
1118     }
1119     int total{0};
1120     int notOptional{0};
1121   };
1122 
1123   bool Rule3Distinguishable(const Procedure &, const Procedure &) const;
1124   const DummyArgument *Rule1DistinguishingArg(
1125       const DummyArguments &, const DummyArguments &) const;
1126   int FindFirstToDistinguishByPosition(
1127       const DummyArguments &, const DummyArguments &) const;
1128   int FindLastToDistinguishByName(
1129       const DummyArguments &, const DummyArguments &) const;
1130   int CountCompatibleWith(const DummyArgument &, const DummyArguments &) const;
1131   int CountNotDistinguishableFrom(
1132       const DummyArgument &, const DummyArguments &) const;
1133   bool Distinguishable(const DummyArgument &, const DummyArgument &) const;
1134   bool Distinguishable(const DummyDataObject &, const DummyDataObject &) const;
1135   bool Distinguishable(const DummyProcedure &, const DummyProcedure &) const;
1136   bool Distinguishable(const FunctionResult &, const FunctionResult &) const;
1137   bool Distinguishable(const TypeAndShape &, const TypeAndShape &) const;
1138   bool IsTkrCompatible(const DummyArgument &, const DummyArgument &) const;
1139   bool IsTkrCompatible(const TypeAndShape &, const TypeAndShape &) const;
1140   const DummyArgument *GetAtEffectivePosition(
1141       const DummyArguments &, int) const;
1142   const DummyArgument *GetPassArg(const Procedure &) const;
1143 
1144   const common::LanguageFeatureControl &features_;
1145 };
1146 
1147 // Simpler distinguishability rules for operators and assignment
1148 bool DistinguishUtils::DistinguishableOpOrAssign(
1149     const Procedure &proc1, const Procedure &proc2) const {
1150   auto &args1{proc1.dummyArguments};
1151   auto &args2{proc2.dummyArguments};
1152   if (args1.size() != args2.size()) {
1153     return true; // C1511: distinguishable based on number of arguments
1154   }
1155   for (std::size_t i{0}; i < args1.size(); ++i) {
1156     if (Distinguishable(args1[i], args2[i])) {
1157       return true; // C1511, C1512: distinguishable based on this arg
1158     }
1159   }
1160   return false;
1161 }
1162 
1163 bool DistinguishUtils::Distinguishable(
1164     const Procedure &proc1, const Procedure &proc2) const {
1165   auto &args1{proc1.dummyArguments};
1166   auto &args2{proc2.dummyArguments};
1167   auto count1{CountDummyProcedures(args1)};
1168   auto count2{CountDummyProcedures(args2)};
1169   if (count1.notOptional > count2.total || count2.notOptional > count1.total) {
1170     return true; // distinguishable based on C1514 rule 2
1171   }
1172   if (Rule3Distinguishable(proc1, proc2)) {
1173     return true; // distinguishable based on C1514 rule 3
1174   }
1175   if (Rule1DistinguishingArg(args1, args2)) {
1176     return true; // distinguishable based on C1514 rule 1
1177   }
1178   int pos1{FindFirstToDistinguishByPosition(args1, args2)};
1179   int name1{FindLastToDistinguishByName(args1, args2)};
1180   if (pos1 >= 0 && pos1 <= name1) {
1181     return true; // distinguishable based on C1514 rule 4
1182   }
1183   int pos2{FindFirstToDistinguishByPosition(args2, args1)};
1184   int name2{FindLastToDistinguishByName(args2, args1)};
1185   if (pos2 >= 0 && pos2 <= name2) {
1186     return true; // distinguishable based on C1514 rule 4
1187   }
1188   return false;
1189 }
1190 
1191 // C1514 rule 3: Procedures are distinguishable if both have a passed-object
1192 // dummy argument and those are distinguishable.
1193 bool DistinguishUtils::Rule3Distinguishable(
1194     const Procedure &proc1, const Procedure &proc2) const {
1195   const DummyArgument *pass1{GetPassArg(proc1)};
1196   const DummyArgument *pass2{GetPassArg(proc2)};
1197   return pass1 && pass2 && Distinguishable(*pass1, *pass2);
1198 }
1199 
1200 // Find a non-passed-object dummy data object in one of the argument lists
1201 // that satisfies C1514 rule 1. I.e. x such that:
1202 // - m is the number of dummy data objects in one that are nonoptional,
1203 //   are not passed-object, that x is TKR compatible with
1204 // - n is the number of non-passed-object dummy data objects, in the other
1205 //   that are not distinguishable from x
1206 // - m is greater than n
1207 const DummyArgument *DistinguishUtils::Rule1DistinguishingArg(
1208     const DummyArguments &args1, const DummyArguments &args2) const {
1209   auto size1{args1.size()};
1210   auto size2{args2.size()};
1211   for (std::size_t i{0}; i < size1 + size2; ++i) {
1212     const DummyArgument &x{i < size1 ? args1[i] : args2[i - size1]};
1213     if (!x.pass && std::holds_alternative<DummyDataObject>(x.u)) {
1214       if (CountCompatibleWith(x, args1) >
1215               CountNotDistinguishableFrom(x, args2) ||
1216           CountCompatibleWith(x, args2) >
1217               CountNotDistinguishableFrom(x, args1)) {
1218         return &x;
1219       }
1220     }
1221   }
1222   return nullptr;
1223 }
1224 
1225 // Find the index of the first nonoptional non-passed-object dummy argument
1226 // in args1 at an effective position such that either:
1227 // - args2 has no dummy argument at that effective position
1228 // - the dummy argument at that position is distinguishable from it
1229 int DistinguishUtils::FindFirstToDistinguishByPosition(
1230     const DummyArguments &args1, const DummyArguments &args2) const {
1231   int effective{0}; // position of arg1 in list, ignoring passed arg
1232   for (std::size_t i{0}; i < args1.size(); ++i) {
1233     const DummyArgument &arg1{args1.at(i)};
1234     if (!arg1.pass && !arg1.IsOptional()) {
1235       const DummyArgument *arg2{GetAtEffectivePosition(args2, effective)};
1236       if (!arg2 || Distinguishable(arg1, *arg2)) {
1237         return i;
1238       }
1239     }
1240     effective += !arg1.pass;
1241   }
1242   return -1;
1243 }
1244 
1245 // Find the index of the last nonoptional non-passed-object dummy argument
1246 // in args1 whose name is such that either:
1247 // - args2 has no dummy argument with that name
1248 // - the dummy argument with that name is distinguishable from it
1249 int DistinguishUtils::FindLastToDistinguishByName(
1250     const DummyArguments &args1, const DummyArguments &args2) const {
1251   std::map<std::string, const DummyArgument *> nameToArg;
1252   for (const auto &arg2 : args2) {
1253     nameToArg.emplace(arg2.name, &arg2);
1254   }
1255   for (int i = args1.size() - 1; i >= 0; --i) {
1256     const DummyArgument &arg1{args1.at(i)};
1257     if (!arg1.pass && !arg1.IsOptional()) {
1258       auto it{nameToArg.find(arg1.name)};
1259       if (it == nameToArg.end() || Distinguishable(arg1, *it->second)) {
1260         return i;
1261       }
1262     }
1263   }
1264   return -1;
1265 }
1266 
1267 // Count the dummy data objects in args that are nonoptional, are not
1268 // passed-object, and that x is TKR compatible with
1269 int DistinguishUtils::CountCompatibleWith(
1270     const DummyArgument &x, const DummyArguments &args) const {
1271   return std::count_if(args.begin(), args.end(), [&](const DummyArgument &y) {
1272     return !y.pass && !y.IsOptional() && IsTkrCompatible(x, y);
1273   });
1274 }
1275 
1276 // Return the number of dummy data objects in args that are not
1277 // distinguishable from x and not passed-object.
1278 int DistinguishUtils::CountNotDistinguishableFrom(
1279     const DummyArgument &x, const DummyArguments &args) const {
1280   return std::count_if(args.begin(), args.end(), [&](const DummyArgument &y) {
1281     return !y.pass && std::holds_alternative<DummyDataObject>(y.u) &&
1282         !Distinguishable(y, x);
1283   });
1284 }
1285 
1286 bool DistinguishUtils::Distinguishable(
1287     const DummyArgument &x, const DummyArgument &y) const {
1288   if (x.u.index() != y.u.index()) {
1289     return true; // different kind: data/proc/alt-return
1290   }
1291   return common::visit(
1292       common::visitors{
1293           [&](const DummyDataObject &z) {
1294             return Distinguishable(z, std::get<DummyDataObject>(y.u));
1295           },
1296           [&](const DummyProcedure &z) {
1297             return Distinguishable(z, std::get<DummyProcedure>(y.u));
1298           },
1299           [&](const AlternateReturn &) { return false; },
1300       },
1301       x.u);
1302 }
1303 
1304 bool DistinguishUtils::Distinguishable(
1305     const DummyDataObject &x, const DummyDataObject &y) const {
1306   using Attr = DummyDataObject::Attr;
1307   if (Distinguishable(x.type, y.type)) {
1308     return true;
1309   } else if (x.attrs.test(Attr::Allocatable) && y.attrs.test(Attr::Pointer) &&
1310       y.intent != common::Intent::In) {
1311     return true;
1312   } else if (y.attrs.test(Attr::Allocatable) && x.attrs.test(Attr::Pointer) &&
1313       x.intent != common::Intent::In) {
1314     return true;
1315   } else if (features_.IsEnabled(
1316                  common::LanguageFeature::DistinguishableSpecifics) &&
1317       (x.attrs.test(Attr::Allocatable) || x.attrs.test(Attr::Pointer)) &&
1318       (y.attrs.test(Attr::Allocatable) || y.attrs.test(Attr::Pointer)) &&
1319       (x.type.type().IsUnlimitedPolymorphic() !=
1320               y.type.type().IsUnlimitedPolymorphic() ||
1321           x.type.type().IsPolymorphic() != y.type.type().IsPolymorphic())) {
1322     // Extension: Per 15.5.2.5(2), an allocatable/pointer dummy and its
1323     // corresponding actual argument must both or neither be polymorphic,
1324     // and must both or neither be unlimited polymorphic.  So when exactly
1325     // one of two dummy arguments is polymorphic or unlimited polymorphic,
1326     // any actual argument that is admissible to one of them cannot also match
1327     // the other one.
1328     return true;
1329   } else {
1330     return false;
1331   }
1332 }
1333 
1334 bool DistinguishUtils::Distinguishable(
1335     const DummyProcedure &x, const DummyProcedure &y) const {
1336   const Procedure &xProc{x.procedure.value()};
1337   const Procedure &yProc{y.procedure.value()};
1338   if (Distinguishable(xProc, yProc)) {
1339     return true;
1340   } else {
1341     const std::optional<FunctionResult> &xResult{xProc.functionResult};
1342     const std::optional<FunctionResult> &yResult{yProc.functionResult};
1343     return xResult ? !yResult || Distinguishable(*xResult, *yResult)
1344                    : yResult.has_value();
1345   }
1346 }
1347 
1348 bool DistinguishUtils::Distinguishable(
1349     const FunctionResult &x, const FunctionResult &y) const {
1350   if (x.u.index() != y.u.index()) {
1351     return true; // one is data object, one is procedure
1352   }
1353   return common::visit(
1354       common::visitors{
1355           [&](const TypeAndShape &z) {
1356             return Distinguishable(z, std::get<TypeAndShape>(y.u));
1357           },
1358           [&](const CopyableIndirection<Procedure> &z) {
1359             return Distinguishable(z.value(),
1360                 std::get<CopyableIndirection<Procedure>>(y.u).value());
1361           },
1362       },
1363       x.u);
1364 }
1365 
1366 bool DistinguishUtils::Distinguishable(
1367     const TypeAndShape &x, const TypeAndShape &y) const {
1368   return !IsTkrCompatible(x, y) && !IsTkrCompatible(y, x);
1369 }
1370 
1371 // Compatibility based on type, kind, and rank
1372 bool DistinguishUtils::IsTkrCompatible(
1373     const DummyArgument &x, const DummyArgument &y) const {
1374   const auto *obj1{std::get_if<DummyDataObject>(&x.u)};
1375   const auto *obj2{std::get_if<DummyDataObject>(&y.u)};
1376   return obj1 && obj2 && IsTkrCompatible(obj1->type, obj2->type);
1377 }
1378 bool DistinguishUtils::IsTkrCompatible(
1379     const TypeAndShape &x, const TypeAndShape &y) const {
1380   return x.type().IsTkCompatibleWith(y.type()) &&
1381       (x.attrs().test(TypeAndShape::Attr::AssumedRank) ||
1382           y.attrs().test(TypeAndShape::Attr::AssumedRank) ||
1383           x.Rank() == y.Rank());
1384 }
1385 
1386 // Return the argument at the given index, ignoring the passed arg
1387 const DummyArgument *DistinguishUtils::GetAtEffectivePosition(
1388     const DummyArguments &args, int index) const {
1389   for (const DummyArgument &arg : args) {
1390     if (!arg.pass) {
1391       if (index == 0) {
1392         return &arg;
1393       }
1394       --index;
1395     }
1396   }
1397   return nullptr;
1398 }
1399 
1400 // Return the passed-object dummy argument of this procedure, if any
1401 const DummyArgument *DistinguishUtils::GetPassArg(const Procedure &proc) const {
1402   for (const auto &arg : proc.dummyArguments) {
1403     if (arg.pass) {
1404       return &arg;
1405     }
1406   }
1407   return nullptr;
1408 }
1409 
1410 bool Distinguishable(const common::LanguageFeatureControl &features,
1411     const Procedure &x, const Procedure &y) {
1412   return DistinguishUtils{features}.Distinguishable(x, y);
1413 }
1414 
1415 bool DistinguishableOpOrAssign(const common::LanguageFeatureControl &features,
1416     const Procedure &x, const Procedure &y) {
1417   return DistinguishUtils{features}.DistinguishableOpOrAssign(x, y);
1418 }
1419 
1420 DEFINE_DEFAULT_CONSTRUCTORS_AND_ASSIGNMENTS(DummyArgument)
1421 DEFINE_DEFAULT_CONSTRUCTORS_AND_ASSIGNMENTS(DummyProcedure)
1422 DEFINE_DEFAULT_CONSTRUCTORS_AND_ASSIGNMENTS(FunctionResult)
1423 DEFINE_DEFAULT_CONSTRUCTORS_AND_ASSIGNMENTS(Procedure)
1424 } // namespace Fortran::evaluate::characteristics
1425 
1426 template class Fortran::common::Indirection<
1427     Fortran::evaluate::characteristics::Procedure, true>;
1428