[Flang][OpenMP] Update declare mapper lookup via use-module (#163860)

- Implemented semantic TODO to catch undeclared mappers.
- Fix mapper lookup to include modules imported through USE.
- Update and add tests.

Fixes #163385.

6 files changed, 120 insertions, 23 deletions

diff --git a/flang/lib/Lower/Bridge.cpp b/flang/lib/Lower/Bridge.cpp
index 20e85a940b18..5bfcff310c23 100644
--- a/flang/lib/Lower/Bridge.cpp
+++ b/flang/lib/Lower/Bridge.cpp
@@ -448,6 +448,13 @@ public:
       }
     });
 
+    // Ensure imported OpenMP declare mappers are materialized at module
+    // scope before lowering any constructs that may reference them.
+    createBuilderOutsideOfFuncOpAndDo([&]() {
+      Fortran::lower::materializeOpenMPDeclareMappers(
+          *this, bridge.getSemanticsContext());
+    });
+
     // Create definitions of intrinsic module constants.
     createBuilderOutsideOfFuncOpAndDo(
         [&]() { createIntrinsicModuleDefinitions(pft); });
diff --git a/flang/lib/Lower/OpenMP/ClauseProcessor.cpp b/flang/lib/Lower/OpenMP/ClauseProcessor.cpp
index 872f31fe45cc..2dd89168ca09 100644
--- a/flang/lib/Lower/OpenMP/ClauseProcessor.cpp
+++ b/flang/lib/Lower/OpenMP/ClauseProcessor.cpp
@@ -1397,10 +1397,14 @@ bool ClauseProcessor::processMap(
     }
     if (mappers) {
       assert(mappers->size() == 1 && "more than one mapper");
-      mapperIdName = mappers->front().v.id().symbol->name().ToString();
-      if (mapperIdName != "default")
-        mapperIdName = converter.mangleName(
-            mapperIdName, mappers->front().v.id().symbol->owner());
+      const semantics::Symbol *mapperSym = mappers->front().v.id().symbol;
+      mapperIdName = mapperSym->name().ToString();
+      if (mapperIdName != "default") {
+        // Mangle with the ultimate owner so that use-associated mapper
+        // identifiers resolve to the same symbol as their defining scope.
+        const semantics::Symbol &ultimate = mapperSym->GetUltimate();
+        mapperIdName = converter.mangleName(mapperIdName, ultimate.owner());
+      }
     }
 
     processMapObjects(stmtCtx, clauseLocation,
diff --git a/flang/lib/Lower/OpenMP/OpenMP.cpp b/flang/lib/Lower/OpenMP/OpenMP.cpp
index 4048aeea37b9..fe80c46c23d0 100644
--- a/flang/lib/Lower/OpenMP/OpenMP.cpp
+++ b/flang/lib/Lower/OpenMP/OpenMP.cpp
@@ -3553,10 +3553,10 @@ genOMP(lower::AbstractConverter &converter, lower::SymMap &symTable,
     TODO(converter.getCurrentLocation(), "OpenMPDeclareSimdConstruct");
 }
 
-static void genOMP(lower::AbstractConverter &converter, lower::SymMap &symTable,
-                   semantics::SemanticsContext &semaCtx,
-                   lower::pft::Evaluation &eval,
-                   const parser::OpenMPDeclareMapperConstruct &construct) {
+static void genOpenMPDeclareMapperImpl(
+    lower::AbstractConverter &converter, semantics::SemanticsContext &semaCtx,
+    const parser::OpenMPDeclareMapperConstruct &construct,
+    const semantics::Symbol *mapperSymOpt = nullptr) {
   mlir::Location loc = converter.genLocation(construct.source);
   fir::FirOpBuilder &firOpBuilder = converter.getFirOpBuilder();
   const parser::OmpArgumentList &args = construct.v.Arguments();
@@ -3572,8 +3572,17 @@ static void genOMP(lower::AbstractConverter &converter, lower::SymMap &symTable,
          "Expected derived type");
 
   std::string mapperNameStr = mapperName;
-  if (auto *sym = converter.getCurrentScope().FindSymbol(mapperNameStr))
+  if (mapperSymOpt && mapperNameStr != "default") {
+    mapperNameStr = converter.mangleName(mapperNameStr, mapperSymOpt->owner());
+  } else if (auto *sym =
+                 converter.getCurrentScope().FindSymbol(mapperNameStr)) {
     mapperNameStr = converter.mangleName(mapperNameStr, sym->owner());
+  }
+
+  // If the mapper op already exists (e.g., created by regular lowering or by
+  // materialization of imported mappers), do not recreate it.
+  if (converter.getModuleOp().lookupSymbol(mapperNameStr))
+    return;
 
   // Save current insertion point before moving to the module scope to create
   // the DeclareMapperOp
@@ -3596,6 +3605,13 @@ static void genOMP(lower::AbstractConverter &converter, lower::SymMap &symTable,
   mlir::omp::DeclareMapperInfoOp::create(firOpBuilder, loc, clauseOps.mapVars);
 }
 
+static void genOMP(lower::AbstractConverter &converter, lower::SymMap &symTable,
+                   semantics::SemanticsContext &semaCtx,
+                   lower::pft::Evaluation &eval,
+                   const parser::OpenMPDeclareMapperConstruct &construct) {
+  genOpenMPDeclareMapperImpl(converter, semaCtx, construct);
+}
+
 static void
 genOMP(lower::AbstractConverter &converter, lower::SymMap &symTable,
        semantics::SemanticsContext &semaCtx, lower::pft::Evaluation &eval,
@@ -4231,3 +4247,36 @@ void Fortran::lower::genOpenMPRequires(mlir::Operation *mod,
     offloadMod.setRequires(mlirFlags);
   }
 }
+
+// Walk scopes and materialize omp.declare_mapper ops for mapper declarations
+// found in imported modules. If \p scope is null, start from the global scope.
+void Fortran::lower::materializeOpenMPDeclareMappers(
+    Fortran::lower::AbstractConverter &converter,
+    semantics::SemanticsContext &semaCtx, const semantics::Scope *scope) {
+  const semantics::Scope &root = scope ? *scope : semaCtx.globalScope();
+
+  // Recurse into child scopes first (modules, submodules, etc.).
+  for (const semantics::Scope &child : root.children())
+    materializeOpenMPDeclareMappers(converter, semaCtx, &child);
+
+  // Only consider module scopes to avoid duplicating local constructs.
+  if (!root.IsModule())
+    return;
+
+  // Only materialize for modules coming from mod files to avoid duplicates.
+  if (!root.symbol() || !root.symbol()->test(semantics::Symbol::Flag::ModFile))
+    return;
+
+  // Scan symbols in this module scope for MapperDetails.
+  for (auto &it : root) {
+    const semantics::Symbol &sym = *it.second;
+    if (auto *md = sym.detailsIf<semantics::MapperDetails>()) {
+      for (const auto *decl : md->GetDeclList()) {
+        if (const auto *mapperDecl =
+                std::get_if<parser::OpenMPDeclareMapperConstruct>(&decl->u)) {
+          genOpenMPDeclareMapperImpl(converter, semaCtx, *mapperDecl, &sym);
+        }
+      }
+    }
+  }
+}
diff --git a/flang/lib/Semantics/mod-file.cpp b/flang/lib/Semantics/mod-file.cpp
index b419864f73b8..840b98dd4213 100644
--- a/flang/lib/Semantics/mod-file.cpp
+++ b/flang/lib/Semantics/mod-file.cpp
@@ -59,6 +59,7 @@ static void PutBound(llvm::raw_ostream &, const Bound &);
 static void PutShapeSpec(llvm::raw_ostream &, const ShapeSpec &);
 static void PutShape(
     llvm::raw_ostream &, const ArraySpec &, char open, char close);
+static void PutMapper(llvm::raw_ostream &, const Symbol &, SemanticsContext &);
 
 static llvm::raw_ostream &PutAttr(llvm::raw_ostream &, Attr);
 static llvm::raw_ostream &PutType(llvm::raw_ostream &, const DeclTypeSpec &);
@@ -938,6 +939,7 @@ void ModFileWriter::PutEntity(llvm::raw_ostream &os, const Symbol &symbol) {
           [&](const ProcEntityDetails &) { PutProcEntity(os, symbol); },
           [&](const TypeParamDetails &) { PutTypeParam(os, symbol); },
           [&](const UserReductionDetails &) { PutUserReduction(os, symbol); },
+          [&](const MapperDetails &) { PutMapper(decls_, symbol, context_); },
           [&](const auto &) {
             common::die("PutEntity: unexpected details: %s",
                 DetailsToString(symbol.details()).c_str());
@@ -1101,6 +1103,16 @@ void ModFileWriter::PutUserReduction(
   }
 }
 
+static void PutMapper(
+    llvm::raw_ostream &os, const Symbol &symbol, SemanticsContext &context) {
+  const auto &details{symbol.get<MapperDetails>()};
+  // Emit each saved DECLARE MAPPER construct as-is, so that consumers of the
+  // module can reparse it and recreate the mapper symbol and semantics state.
+  for (const auto *decl : details.GetDeclList()) {
+    Unparse(os, *decl, context.langOptions());
+  }
+}
+
 void PutInit(llvm::raw_ostream &os, const Symbol &symbol, const MaybeExpr &init,
     const parser::Expr *unanalyzed, SemanticsContext &context) {
   if (IsNamedConstant(symbol) || symbol.owner().IsDerivedType()) {
diff --git a/flang/lib/Semantics/resolve-names.cpp b/flang/lib/Semantics/resolve-names.cpp
index 09ec951a422c..ea0d38c573af 100644
--- a/flang/lib/Semantics/resolve-names.cpp
+++ b/flang/lib/Semantics/resolve-names.cpp
@@ -1852,21 +1852,25 @@ bool OmpVisitor::Pre(const parser::OmpMapClause &x) {
       // TODO: Do we need a specific flag or type here, to distinghuish against
       // other ConstructName things? Leaving this for the full implementation
       // of mapper lowering.
-      auto *misc{symbol->detailsIf<MiscDetails>()};
-      if (!misc || misc->kind() != MiscDetails::Kind::ConstructName)
+      auto &ultimate{symbol->GetUltimate()};
+      auto *misc{ultimate.detailsIf<MiscDetails>()};
+      auto *md{ultimate.detailsIf<MapperDetails>()};
+      if (!md && (!misc || misc->kind() != MiscDetails::Kind::ConstructName))
         context().Say(mapper->v.source,
             "Name '%s' should be a mapper name"_err_en_US, mapper->v.source);
       else
         mapper->v.symbol = symbol;
     } else {
-      mapper->v.symbol =
-          &MakeSymbol(mapper->v, MiscDetails{MiscDetails::Kind::ConstructName});
-      // TODO: When completing the implementation, we probably want to error if
-      // the symbol is not declared, but right now, testing that the TODO for
-      // OmpMapClause happens is obscured by the TODO for declare mapper, so
-      // leaving this out. Remove the above line once the declare mapper is
-      // implemented. context().Say(mapper->v.source, "'%s' not
-      // declared"_err_en_US, mapper->v.source);
+      // Allow the special 'default' mapper identifier without prior
+      // declaration so lowering can recognize and handle it. Emit an
+      // error for any other missing mapper identifier.
+      if (mapper->v.source.ToString() == "default") {
+        mapper->v.symbol = &MakeSymbol(
+            mapper->v, MiscDetails{MiscDetails::Kind::ConstructName});
+      } else {
+        context().Say(
+            mapper->v.source, "'%s' not declared"_err_en_US, mapper->v.source);
+      }
     }
   }
   return true;
@@ -1880,8 +1884,15 @@ void OmpVisitor::ProcessMapperSpecifier(const parser::OmpMapperSpecifier &spec,
   // the type has been fully processed.
   BeginDeclTypeSpec();
   auto &mapperName{std::get<std::string>(spec.t)};
-  MakeSymbol(parser::CharBlock(mapperName), Attrs{},
-      MiscDetails{MiscDetails::Kind::ConstructName});
+  // Create or update the mapper symbol with MapperDetails and
+  // keep track of the declarative construct for module emission.
+  Symbol &mapperSym{MakeSymbol(parser::CharBlock(mapperName), Attrs{})};
+  if (auto *md{mapperSym.detailsIf<MapperDetails>()}) {
+    md->AddDecl(declaratives_.back());
+  } else if (mapperSym.has<UnknownDetails>() || mapperSym.has<MiscDetails>()) {
+    mapperSym.set_details(MapperDetails{});
+    mapperSym.get<MapperDetails>().AddDecl(declaratives_.back());
+  }
   PushScope(Scope::Kind::OtherConstruct, nullptr);
   Walk(std::get<parser::TypeSpec>(spec.t));
   auto &varName{std::get<parser::Name>(spec.t)};
@@ -3611,10 +3622,20 @@ void ModuleVisitor::Post(const parser::UseStmt &x) {
           rename.u);
     }
     for (const auto &[name, symbol] : *useModuleScope_) {
+      // Default USE imports public names, excluding intrinsic-only and most
+      // miscellaneous details. Allow OpenMP mapper identifiers represented
+      // as MapperDetails, and also legacy MiscDetails::ConstructName.
+      bool isMapper{symbol->has<MapperDetails>()};
+      if (!isMapper) {
+        if (const auto *misc{symbol->detailsIf<MiscDetails>()}) {
+          isMapper = misc->kind() == MiscDetails::Kind::ConstructName;
+        }
+      }
       if (symbol->attrs().test(Attr::PUBLIC) && !IsUseRenamed(symbol->name()) &&
           (!symbol->implicitAttrs().test(Attr::INTRINSIC) ||
               symbol->has<UseDetails>()) &&
-          !symbol->has<MiscDetails>() && useNames.count(name) == 0) {
+          (!symbol->has<MiscDetails>() || isMapper) &&
+          useNames.count(name) == 0) {
         SourceName location{x.moduleName.source};
         if (auto *localSymbol{FindInScope(name)}) {
           DoAddUse(location, localSymbol->name(), *localSymbol, *symbol);
diff --git a/flang/lib/Semantics/symbol.cpp b/flang/lib/Semantics/symbol.cpp
index 0ec44b7c4049..ed0715a422e7 100644
--- a/flang/lib/Semantics/symbol.cpp
+++ b/flang/lib/Semantics/symbol.cpp
@@ -338,7 +338,8 @@ std::string DetailsToString(const Details &details) {
           [](const TypeParamDetails &) { return "TypeParam"; },
           [](const MiscDetails &) { return "Misc"; },
           [](const AssocEntityDetails &) { return "AssocEntity"; },
-          [](const UserReductionDetails &) { return "UserReductionDetails"; }},
+          [](const UserReductionDetails &) { return "UserReductionDetails"; },
+          [](const MapperDetails &) { return "MapperDetails"; }},
       details);
 }
 
@@ -379,6 +380,7 @@ bool Symbol::CanReplaceDetails(const Details &details) const {
             [&](const UserReductionDetails &) {
               return has<UserReductionDetails>();
             },
+            [&](const MapperDetails &) { return has<MapperDetails>(); },
             [](const auto &) { return false; },
         },
         details);
@@ -685,6 +687,8 @@ llvm::raw_ostream &operator<<(llvm::raw_ostream &os, const Details &details) {
               DumpType(os, type);
             }
           },
+          // Avoid recursive streaming for MapperDetails; nothing more to dump
+          [&](const MapperDetails &) {},
           [&](const auto &x) { os << x; },
       },
       details);