flang/lib/Semantics/check-case.cpp

   1 //===-- lib/Semantics/check-case.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 "check-case.h"
  10 #include "flang/Common/idioms.h"
  11 #include "flang/Common/reference.h"
  12 #include "flang/Common/template.h"
  13 #include "flang/Evaluate/fold.h"
  14 #include "flang/Evaluate/type.h"
  15 #include "flang/Parser/parse-tree.h"
  16 #include "flang/Semantics/semantics.h"
  17 #include "flang/Semantics/tools.h"
  18 #include <tuple>
  19
  20 namespace Fortran::semantics {
  21
  22 template <typename T> class CaseValues {
  23 public:
  24   CaseValues(SemanticsContext &c, const evaluate::DynamicType &t)
  25       : context_{c}, caseExprType_{t} {}
  26
  27   void Check(const std::list<parser::CaseConstruct::Case> &cases) {
  28     for (const parser::CaseConstruct::Case &c : cases) {
  29       AddCase(c);
  30     }
  31     if (!hasErrors_) {
  32       cases_.sort(Comparator{});
  33       if (!AreCasesDisjoint()) { // C1149
  34         ReportConflictingCases();
  35       }
  36     }
  37   }
  38
  39 private:
  40   using Value = evaluate::Scalar<T>;
  41
  42   void AddCase(const parser::CaseConstruct::Case &c) {
  43     const auto &stmt{std::get<parser::Statement<parser::CaseStmt>>(c.t)};
  44     const parser::CaseStmt &caseStmt{stmt.statement};
  45     const auto &selector{std::get<parser::CaseSelector>(caseStmt.t)};
  46     common::visit(
  47         common::visitors{
  48             [&](const std::list<parser::CaseValueRange> &ranges) {
  49               for (const auto &range : ranges) {
  50                 auto pair{ComputeBounds(range)};
  51                 if (pair.first && pair.second && *pair.first > *pair.second) {
  52                   context_.Warn(common::UsageWarning::EmptyCase, stmt.source,
  53                       "CASE has lower bound greater than upper bound"_warn_en_US);
  54                 } else {
  55                   if constexpr (T::category == TypeCategory::Logical) { // C1148
  56                     if ((pair.first || pair.second) &&
  57                         (!pair.first || !pair.second ||
  58                             *pair.first != *pair.second)) {
  59                       context_.Say(stmt.source,
  60                           "CASE range is not allowed for LOGICAL"_err_en_US);
  61                     }
  62                   }
  63                   cases_.emplace_back(stmt);
  64                   cases_.back().lower = std::move(pair.first);
  65                   cases_.back().upper = std::move(pair.second);
  66                 }
  67               }
  68             },
  69             [&](const parser::Default &) { cases_.emplace_front(stmt); },
  70         },
  71         selector.u);
  72   }
  73
  74   std::optional<Value> GetValue(const parser::CaseValue &caseValue) {
  75     const parser::Expr &expr{caseValue.thing.thing.value()};
  76     auto *x{expr.typedExpr.get()};
  77     if (x && x->v) { // C1147
  78       auto type{x->v->GetType()};
  79       if (type && type->category() == caseExprType_.category() &&
  80           (type->category() != TypeCategory::Character ||
  81               type->kind() == caseExprType_.kind())) {
  82         parser::Messages buffer; // discarded folding messages
  83         parser::ContextualMessages foldingMessages{expr.source, &buffer};
  84         evaluate::FoldingContext foldingContext{
  85             context_.foldingContext(), foldingMessages};
  86         auto folded{evaluate::Fold(foldingContext, SomeExpr{*x->v})};
  87         if (auto converted{evaluate::Fold(foldingContext,
  88                 evaluate::ConvertToType(T::GetType(), SomeExpr{folded}))}) {
  89           if (auto value{evaluate::GetScalarConstantValue<T>(*converted)}) {
  90             auto back{evaluate::Fold(foldingContext,
  91                 evaluate::ConvertToType(*type, SomeExpr{*converted}))};
  92             if (back == folded) {
  93               x->v = converted;
  94               return value;
  95             } else {
  96               context_.Warn(common::UsageWarning::CaseOverflow, expr.source,
  97                   "CASE value (%s) overflows type (%s) of SELECT CASE expression"_warn_en_US,
  98                   folded.AsFortran(), caseExprType_.AsFortran());
  99               hasErrors_ = true;
 100               return std::nullopt;
 101             }
 102           }
 103         }
 104         context_.Say(expr.source,
 105             "CASE value (%s) must be a constant scalar"_err_en_US,
 106             x->v->AsFortran());
 107       } else {
 108         std::string typeStr{type ? type->AsFortran() : "typeless"s};
 109         context_.Say(expr.source,
 110             "CASE value has type '%s' which is not compatible with the SELECT CASE expression's type '%s'"_err_en_US,
 111             typeStr, caseExprType_.AsFortran());
 112       }
 113       hasErrors_ = true;
 114     }
 115     return std::nullopt;
 116   }
 117
 118   using PairOfValues = std::pair<std::optional<Value>, std::optional<Value>>;
 119   PairOfValues ComputeBounds(const parser::CaseValueRange &range) {
 120     return common::visit(
 121         common::visitors{
 122             [&](const parser::CaseValue &x) {
 123               auto value{GetValue(x)};
 124               return PairOfValues{value, value};
 125             },
 126             [&](const parser::CaseValueRange::Range &x) {
 127               std::optional<Value> lo, hi;
 128               if (x.lower) {
 129                 lo = GetValue(*x.lower);
 130               }
 131               if (x.upper) {
 132                 hi = GetValue(*x.upper);
 133               }
 134               if ((x.lower && !lo) || (x.upper && !hi)) {
 135                 return PairOfValues{}; // error case
 136               }
 137               return PairOfValues{std::move(lo), std::move(hi)};
 138             },
 139         },
 140         range.u);
 141   }
 142
 143   struct Case {
 144     explicit Case(const parser::Statement<parser::CaseStmt> &s) : stmt{s} {}
 145     bool IsDefault() const { return !lower && !upper; }
 146     std::string AsFortran() const {
 147       std::string result;
 148       {
 149         llvm::raw_string_ostream bs{result};
 150         if (lower) {
 151           evaluate::Constant<T>{*lower}.AsFortran(bs << '(');
 152           if (!upper) {
 153             bs << ':';
 154           } else if (*lower != *upper) {
 155             evaluate::Constant<T>{*upper}.AsFortran(bs << ':');
 156           }
 157           bs << ')';
 158         } else if (upper) {
 159           evaluate::Constant<T>{*upper}.AsFortran(bs << "(:") << ')';
 160         } else {
 161           bs << "DEFAULT";
 162         }
 163       }
 164       return result;
 165     }
 166
 167     const parser::Statement<parser::CaseStmt> &stmt;
 168     std::optional<Value> lower, upper;
 169   };
 170
 171   // Defines a comparator for use with std::list<>::sort().
 172   // Returns true if and only if the highest value in range x is less
 173   // than the least value in range y.  The DEFAULT case is arbitrarily
 174   // defined to be less than all others.  When two ranges overlap,
 175   // neither is less than the other.
 176   struct Comparator {
 177     bool operator()(const Case &x, const Case &y) const {
 178       if (x.IsDefault()) {
 179         return !y.IsDefault();
 180       } else {
 181         return x.upper && y.lower && *x.upper < *y.lower;
 182       }
 183     }
 184   };
 185
 186   bool AreCasesDisjoint() const {
 187     auto endIter{cases_.end()};
 188     for (auto iter{cases_.begin()}; iter != endIter; ++iter) {
 189       auto next{iter};
 190       if (++next != endIter && !Comparator{}(*iter, *next)) {
 191         return false;
 192       }
 193     }
 194     return true;
 195   }
 196
 197   // This has quadratic time, but only runs in error cases
 198   void ReportConflictingCases() {
 199     for (auto iter{cases_.begin()}; iter != cases_.end(); ++iter) {
 200       parser::Message *msg{nullptr};
 201       for (auto p{cases_.begin()}; p != cases_.end(); ++p) {
 202         if (p->stmt.source.begin() < iter->stmt.source.begin() &&
 203             !Comparator{}(*p, *iter) && !Comparator{}(*iter, *p)) {
 204           if (!msg) {
 205             msg = &context_.Say(iter->stmt.source,
 206                 "CASE %s conflicts with previous cases"_err_en_US,
 207                 iter->AsFortran());
 208           }
 209           msg->Attach(
 210               p->stmt.source, "Conflicting CASE %s"_en_US, p->AsFortran());
 211         }
 212       }
 213     }
 214   }
 215
 216   SemanticsContext &context_;
 217   const evaluate::DynamicType &caseExprType_;
 218   std::list<Case> cases_;
 219   bool hasErrors_{false};
 220 };
 221
 222 template <TypeCategory CAT> struct TypeVisitor {
 223   using Result = bool;
 224   using Types = evaluate::CategoryTypes<CAT>;
 225   template <typename T> Result Test() {
 226     if (T::kind == exprType.kind()) {
 227       CaseValues<T>(context, exprType).Check(caseList);
 228       return true;
 229     } else {
 230       return false;
 231     }
 232   }
 233   SemanticsContext &context;
 234   const evaluate::DynamicType &exprType;
 235   const std::list<parser::CaseConstruct::Case> &caseList;
 236 };
 237
 238 void CaseChecker::Enter(const parser::CaseConstruct &construct) {
 239   const auto &selectCaseStmt{
 240       std::get<parser::Statement<parser::SelectCaseStmt>>(construct.t)};
 241   const auto &selectCase{selectCaseStmt.statement};
 242   const auto &selectExpr{
 243       std::get<parser::Scalar<parser::Expr>>(selectCase.t).thing};
 244   const auto *x{GetExpr(context_, selectExpr)};
 245   if (!x) {
 246     return; // expression semantics failed
 247   }
 248   if (auto exprType{x->GetType()}) {
 249     const auto &caseList{
 250         std::get<std::list<parser::CaseConstruct::Case>>(construct.t)};
 251     switch (exprType->category()) {
 252     case TypeCategory::Integer:
 253       common::SearchTypes(
 254           TypeVisitor<TypeCategory::Integer>{context_, *exprType, caseList});
 255       return;
 256     case TypeCategory::Logical:
 257       CaseValues<evaluate::Type<TypeCategory::Logical, 1>>{context_, *exprType}
 258           .Check(caseList);
 259       return;
 260     case TypeCategory::Character:
 261       common::SearchTypes(
 262           TypeVisitor<TypeCategory::Character>{context_, *exprType, caseList});
 263       return;
 264     default:
 265       break;
 266     }
 267   }
 268   context_.Say(selectExpr.source,
 269       "SELECT CASE expression must be integer, logical, or character"_err_en_US);
 270 }
 271 } // namespace Fortran::semantics