[flang][OpenMP] Allow utility constructs in specification part (#121509)

Allow utility constructs (error and nothing) to appear in the
specification part as well as the execution part. The exception is
"ERROR AT(EXECUTION)" which should only be in the execution part.
In case of ambiguity (the boundary between the specification and the
execution part), utility constructs will be parsed as belonging to the
specification part. In such cases move them to the execution part in the
OpenMP canonicalization code.

Author: kparzysz

flang/examples/FlangOmpReport/FlangOmpReportVisitor.cpp

@@ -106,10 +106,16 @@ std::string OpenMPCounterVisitor::getName(const OmpWrapperType &w) {
   return getName(*std::get<const OpenMPDeclarativeConstruct *>(w));
 }
 std::string OpenMPCounterVisitor::getName(const OpenMPDeclarativeConstruct &c) {
-  return std::visit(
-      [&](const auto &o) -> std::string {
-        const CharBlock &source{std::get<Verbatim>(o.t).source};
-        return normalize_construct_name(source.ToString());
+  return std::visit( //
+      Fortran::common::visitors{
+          [&](const OpenMPUtilityConstruct &o) -> std::string {
+            const CharBlock &source{o.source};
+            return normalize_construct_name(source.ToString());
+          },
+          [&](const auto &o) -> std::string {
+            const CharBlock &source{std::get<Verbatim>(o.t).source};
+            return normalize_construct_name(source.ToString());
+          },
       },
       c.u);
 }

flang/include/flang/Parser/parse-tree.h

@@ -4342,7 +4342,7 @@ struct OpenMPDeclarativeConstruct {
   std::variant<OpenMPDeclarativeAllocate, OpenMPDeclareMapperConstruct,
       OpenMPDeclareReductionConstruct, OpenMPDeclareSimdConstruct,
       OpenMPDeclareTargetConstruct, OpenMPThreadprivate,
-      OpenMPRequiresConstruct>
+      OpenMPRequiresConstruct, OpenMPUtilityConstruct>
       u;
 };
 

flang/lib/Lower/OpenMP/OpenMP.cpp

@@ -2586,6 +2586,10 @@ static void genOMPDispatch(lower::AbstractConverter &converter,
 //===----------------------------------------------------------------------===//
 // OpenMPDeclarativeConstruct visitors
 //===----------------------------------------------------------------------===//
+static void genOMP(lower::AbstractConverter &converter, lower::SymMap &symTable,
+                   semantics::SemanticsContext &semaCtx,
+                   lower::pft::Evaluation &eval,
+                   const parser::OpenMPUtilityConstruct &);
 
 static void
 genOMP(lower::AbstractConverter &converter, lower::SymMap &symTable,

flang/lib/Parser/openmp-parsers.cpp

@@ -1090,7 +1090,9 @@ TYPE_PARSER(startOmpLine >>
             construct<OpenMPDeclarativeConstruct>(
                 Parser<OpenMPRequiresConstruct>{}) ||
             construct<OpenMPDeclarativeConstruct>(
-                Parser<OpenMPThreadprivate>{})) /
+                Parser<OpenMPThreadprivate>{}) ||
+            construct<OpenMPDeclarativeConstruct>(
+                Parser<OpenMPUtilityConstruct>{})) /
             endOmpLine))
 
 // Block Construct

flang/lib/Parser/unparse.cpp

@@ -2631,81 +2631,64 @@ class UnparseVisitor {
     }
   }
   void Unparse(const OpenMPDeclareReductionConstruct &x) {
+    BeginOpenMP();
+    Word("!$OMP DECLARE REDUCTION ");
     Put("(");
     Walk(std::get<OmpReductionIdentifier>(x.t)), Put(" : ");
     Walk(std::get<std::list<DeclarationTypeSpec>>(x.t), ","), Put(" : ");
     Walk(std::get<OmpReductionCombiner>(x.t));
     Put(")");
     Walk(std::get<std::optional<OmpReductionInitializerClause>>(x.t));
+    EndOpenMP();
   }
-  bool Pre(const OpenMPDeclarativeConstruct &x) {
+
+  void Unparse(const OpenMPDeclareMapperConstruct &z) {
     BeginOpenMP();
-    Word("!$OMP ");
-    return common::visit(
-        common::visitors{
-            [&](const OpenMPDeclarativeAllocate &z) {
-              Word("ALLOCATE (");
-              Walk(std::get<OmpObjectList>(z.t));
-              Put(")");
-              Walk(std::get<OmpClauseList>(z.t));
-              Put("\n");
-              EndOpenMP();
-              return false;
-            },
-            [&](const OpenMPDeclareMapperConstruct &z) {
-              Word("DECLARE MAPPER (");
-              const auto &spec{std::get<OmpDeclareMapperSpecifier>(z.t)};
-              if (auto mapname{std::get<std::optional<Name>>(spec.t)}) {
-                Walk(mapname);
-                Put(":");
-              }
-              Walk(std::get<TypeSpec>(spec.t));
-              Put("::");
-              Walk(std::get<Name>(spec.t));
-              Put(")");
+    Word("!$OMP DECLARE MAPPER (");
+    const auto &spec{std::get<OmpDeclareMapperSpecifier>(z.t)};
+    if (auto mapname{std::get<std::optional<Name>>(spec.t)}) {
+      Walk(mapname);
+      Put(":");
+    }
+    Walk(std::get<TypeSpec>(spec.t));
+    Put("::");
+    Walk(std::get<Name>(spec.t));
+    Put(")");
 
-              Walk(std::get<OmpClauseList>(z.t));
-              Put("\n");
-              return false;
-            },
-            [&](const OpenMPDeclareReductionConstruct &) {
-              Word("DECLARE REDUCTION ");
-              return true;
-            },
-            [&](const OpenMPDeclareSimdConstruct &y) {
-              Word("DECLARE SIMD ");
-              Walk("(", std::get<std::optional<Name>>(y.t), ")");
-              Walk(std::get<OmpClauseList>(y.t));
-              Put("\n");
-              EndOpenMP();
-              return false;
-            },
-            [&](const OpenMPDeclareTargetConstruct &) {
-              Word("DECLARE TARGET ");
-              return true;
-            },
-            [&](const OpenMPRequiresConstruct &y) {
-              Word("REQUIRES ");
-              Walk(std::get<OmpClauseList>(y.t));
-              Put("\n");
-              EndOpenMP();
-              return false;
-            },
-            [&](const OpenMPThreadprivate &) {
-              Word("THREADPRIVATE (");
-              return true;
-            },
-        },
-        x.u);
+    Walk(std::get<OmpClauseList>(z.t));
+    Put("\n");
+    EndOpenMP();
+  }
+  void Unparse(const OpenMPDeclareSimdConstruct &y) {
+    BeginOpenMP();
+    Word("!$OMP DECLARE SIMD ");
+    Walk("(", std::get<std::optional<Name>>(y.t), ")");
+    Walk(std::get<OmpClauseList>(y.t));
+    Put("\n");
+    EndOpenMP();
   }
-  void Post(const OpenMPDeclarativeConstruct &) {
+  void Unparse(const OpenMPDeclareTargetConstruct &x) {
+    BeginOpenMP();
+    Word("!$OMP DECLARE TARGET ");
+    Walk(std::get<parser::OmpDeclareTargetSpecifier>(x.t));
     Put("\n");
     EndOpenMP();
   }
-  void Post(const OpenMPThreadprivate &) {
+  void Unparse(const OpenMPRequiresConstruct &y) {
+    BeginOpenMP();
+    Word("!$OMP REQUIRES ");
+    Walk(std::get<OmpClauseList>(y.t));
+    Put("\n");
+    EndOpenMP();
+  }
+  void Unparse(const OpenMPThreadprivate &x) {
+    BeginOpenMP();
+    Word("!$OMP THREADPRIVATE (");
+    Walk(std::get<parser::OmpObjectList>(x.t));
     Put(")\n");
     EndOpenMP();
   }
+
   bool Pre(const OmpMessageClause &x) {
     Walk(x.v);
     return false;

flang/lib/Semantics/canonicalize-omp.cpp

@@ -50,6 +50,43 @@ class CanonicalizationOfOmp {
 
   void Post(parser::ExecutionPart &body) { RewriteOmpAllocations(body); }
 
+  // Pre-visit all constructs that have both a specification part and
+  // an execution part, and store the connection between the two.
+  bool Pre(parser::BlockConstruct &x) {
+    auto *spec = &std::get<parser::BlockSpecificationPart>(x.t).v;
+    auto *block = &std::get<parser::Block>(x.t);
+    blockForSpec_.insert(std::make_pair(spec, block));
+    return true;
+  }
+  bool Pre(parser::MainProgram &x) {
+    auto *spec = &std::get<parser::SpecificationPart>(x.t);
+    auto *block = &std::get<parser::ExecutionPart>(x.t).v;
+    blockForSpec_.insert(std::make_pair(spec, block));
+    return true;
+  }
+  bool Pre(parser::FunctionSubprogram &x) {
+    auto *spec = &std::get<parser::SpecificationPart>(x.t);
+    auto *block = &std::get<parser::ExecutionPart>(x.t).v;
+    blockForSpec_.insert(std::make_pair(spec, block));
+    return true;
+  }
+  bool Pre(parser::SubroutineSubprogram &x) {
+    auto *spec = &std::get<parser::SpecificationPart>(x.t);
+    auto *block = &std::get<parser::ExecutionPart>(x.t).v;
+    blockForSpec_.insert(std::make_pair(spec, block));
+    return true;
+  }
+  bool Pre(parser::SeparateModuleSubprogram &x) {
+    auto *spec = &std::get<parser::SpecificationPart>(x.t);
+    auto *block = &std::get<parser::ExecutionPart>(x.t).v;
+    blockForSpec_.insert(std::make_pair(spec, block));
+    return true;
+  }
+
+  void Post(parser::SpecificationPart &spec) {
+    CanonicalizeUtilityConstructs(spec);
+  }
+
 private:
   template <typename T> T *GetConstructIf(parser::ExecutionPartConstruct &x) {
     if (auto *y{std::get_if<parser::ExecutableConstruct>(&x.u)}) {
@@ -155,6 +192,131 @@ class CanonicalizationOfOmp {
     }
   }
 
+  // Canonicalization of utility constructs.
+  //
+  // This addresses the issue of utility constructs that appear at the
+  // boundary between the specification and the execution parts, e.g.
+  //   subroutine foo
+  //     integer :: x     ! Specification
+  //     !$omp nothing
+  //     x = 1            ! Execution
+  //     ...
+  //   end
+  //
+  // Utility constructs (error and nothing) can appear in both the
+  // specification part and the execution part, except "error at(execution)",
+  // which cannot be present in the specification part (whereas any utility
+  // construct can be in the execution part).
+  // When a utility construct is at the boundary, it should preferably be
+  // parsed as an element of the execution part, but since the specification
+  // part is parsed first, the utility construct ends up belonging to the
+  // specification part.
+  //
+  // To allow the likes of the following code to compile, move all utility
+  // construct that are at the end of the specification part to the beginning
+  // of the execution part.
+  //
+  // subroutine foo
+  //   !$omp error at(execution)  ! Initially parsed as declarative construct.
+  //                              ! Move it to the execution part.
+  // end
+
+  void CanonicalizeUtilityConstructs(parser::SpecificationPart &spec) {
+    auto found = blockForSpec_.find(&spec);
+    if (found == blockForSpec_.end()) {
+      // There is no corresponding execution part, so there is nothing to do.
+      return;
+    }
+    parser::Block &block = *found->second;
+
+    // There are two places where an OpenMP declarative construct can
+    // show up in the tuple in specification part:
+    // (1) in std::list<OpenMPDeclarativeConstruct>, or
+    // (2) in std::list<DeclarationConstruct>.
+    // The case (1) is only possible is the list (2) is empty.
+
+    auto &omps =
+        std::get<std::list<parser::OpenMPDeclarativeConstruct>>(spec.t);
+    auto &decls = std::get<std::list<parser::DeclarationConstruct>>(spec.t);
+
+    if (!decls.empty()) {
+      MoveUtilityConstructsFromDecls(decls, block);
+    } else {
+      MoveUtilityConstructsFromOmps(omps, block);
+    }
+  }
+
+  void MoveUtilityConstructsFromDecls(
+      std::list<parser::DeclarationConstruct> &decls, parser::Block &block) {
+    // Find the trailing range of DeclarationConstructs that are OpenMP
+    // utility construct, that are to be moved to the execution part.
+    std::list<parser::DeclarationConstruct>::reverse_iterator rlast = [&]() {
+      for (auto rit = decls.rbegin(), rend = decls.rend(); rit != rend; ++rit) {
+        parser::DeclarationConstruct &dc = *rit;
+        if (!std::holds_alternative<parser::SpecificationConstruct>(dc.u)) {
+          return rit;
+        }
+        auto &sc = std::get<parser::SpecificationConstruct>(dc.u);
+        using OpenMPDeclarativeConstruct =
+            common::Indirection<parser::OpenMPDeclarativeConstruct>;
+        if (!std::holds_alternative<OpenMPDeclarativeConstruct>(sc.u)) {
+          return rit;
+        }
+        // Got OpenMPDeclarativeConstruct. If it's not a utility construct
+        // then stop.
+        auto &odc = std::get<OpenMPDeclarativeConstruct>(sc.u).value();
+        if (!std::holds_alternative<parser::OpenMPUtilityConstruct>(odc.u)) {
+          return rit;
+        }
+      }
+      return decls.rend();
+    }();
+
+    std::transform(decls.rbegin(), rlast, std::front_inserter(block),
+        [](parser::DeclarationConstruct &dc) {
+          auto &sc = std::get<parser::SpecificationConstruct>(dc.u);
+          using OpenMPDeclarativeConstruct =
+              common::Indirection<parser::OpenMPDeclarativeConstruct>;
+          auto &oc = std::get<OpenMPDeclarativeConstruct>(sc.u).value();
+          auto &ut = std::get<parser::OpenMPUtilityConstruct>(oc.u);
+
+          return parser::ExecutionPartConstruct(parser::ExecutableConstruct(
+              common::Indirection(parser::OpenMPConstruct(std::move(ut)))));
+        });
+
+    decls.erase(rlast.base(), decls.end());
+  }
+
+  void MoveUtilityConstructsFromOmps(
+      std::list<parser::OpenMPDeclarativeConstruct> &omps,
+      parser::Block &block) {
+    using OpenMPDeclarativeConstruct = parser::OpenMPDeclarativeConstruct;
+    // Find the trailing range of OpenMPDeclarativeConstruct that are OpenMP
+    // utility construct, that are to be moved to the execution part.
+    std::list<OpenMPDeclarativeConstruct>::reverse_iterator rlast = [&]() {
+      for (auto rit = omps.rbegin(), rend = omps.rend(); rit != rend; ++rit) {
+        OpenMPDeclarativeConstruct &dc = *rit;
+        if (!std::holds_alternative<parser::OpenMPUtilityConstruct>(dc.u)) {
+          return rit;
+        }
+      }
+      return omps.rend();
+    }();
+
+    std::transform(omps.rbegin(), rlast, std::front_inserter(block),
+        [](parser::OpenMPDeclarativeConstruct &dc) {
+          auto &ut = std::get<parser::OpenMPUtilityConstruct>(dc.u);
+          return parser::ExecutionPartConstruct(parser::ExecutableConstruct(
+              common::Indirection(parser::OpenMPConstruct(std::move(ut)))));
+        });
+
+    omps.erase(rlast.base(), omps.end());
+  }
+
+  // Mapping from the specification parts to the blocks that follow in the
+  // same construct. This is for converting utility constructs to executable
+  // constructs.
+  std::map<parser::SpecificationPart *, parser::Block *> blockForSpec_;
   parser::Messages &messages_;
 };
 

flang/lib/Semantics/check-omp-structure.cpp

@@ -614,6 +614,14 @@ void OmpStructureChecker::Leave(const parser::OpenMPConstruct &) {
   deferredNonVariables_.clear();
 }
 
+void OmpStructureChecker::Enter(const parser::OpenMPDeclarativeConstruct &x) {
+  EnterDirectiveNest(DeclarativeNest);
+}
+
+void OmpStructureChecker::Leave(const parser::OpenMPDeclarativeConstruct &x) {
+  ExitDirectiveNest(DeclarativeNest);
+}
+
 void OmpStructureChecker::Enter(const parser::OpenMPLoopConstruct &x) {
   loopStack_.push_back(&x);
   const auto &beginLoopDir{std::get<parser::OmpBeginLoopDirective>(x.t)};
@@ -1697,6 +1705,16 @@ void OmpStructureChecker::Leave(const parser::OmpErrorDirective &x) {
   dirContext_.pop_back();
 }
 
+void OmpStructureChecker::Enter(const parser::OmpClause::At &x) {
+  CheckAllowedClause(llvm::omp::Clause::OMPC_at);
+  if (GetDirectiveNest(DeclarativeNest) > 0) {
+    if (x.v.v == parser::OmpAtClause::ActionTime::Execution) {
+      context_.Say(GetContext().clauseSource,
+          "The ERROR directive with AT(EXECUTION) cannot appear in the specification part"_err_en_US);
+    }
+  }
+}
+
 void OmpStructureChecker::Enter(const parser::OpenMPExecutableAllocate &x) {
   isPredefinedAllocator = true;
   const auto &dir{std::get<parser::Verbatim>(x.t)};
@@ -2856,7 +2874,6 @@ CHECK_SIMPLE_CLAUSE(Init, OMPC_init)
 CHECK_SIMPLE_CLAUSE(Use, OMPC_use)
 CHECK_SIMPLE_CLAUSE(Novariants, OMPC_novariants)
 CHECK_SIMPLE_CLAUSE(Nocontext, OMPC_nocontext)
-CHECK_SIMPLE_CLAUSE(At, OMPC_at)
 CHECK_SIMPLE_CLAUSE(Severity, OMPC_severity)
 CHECK_SIMPLE_CLAUSE(Message, OMPC_message)
 CHECK_SIMPLE_CLAUSE(Filter, OMPC_filter)