[Flang][OpenMP] Update declare mapper lookup via use-module

flang/include/flang/Lower/OpenMP.h

@@ -97,6 +97,13 @@ bool markOpenMPDeferredDeclareTargetFunctions(
     AbstractConverter &);
 void genOpenMPRequires(mlir::Operation *, const Fortran::semantics::Symbol *);
 
+// Materialize omp.declare_mapper ops for mapper declarations found in
+// imported modules. If \p scope is null, materialize for the whole
+// semantics global scope; otherwise, operate recursively starting at \p scope.
+void materializeOpenMPDeclareMappers(
+    Fortran::lower::AbstractConverter &, Fortran::semantics::SemanticsContext &,
+    const Fortran::semantics::Scope *scope = nullptr);
+
 } // namespace lower
 } // namespace Fortran
 

flang/include/flang/Semantics/symbol.h

@@ -777,14 +777,32 @@ class UserReductionDetails {
   DeclVector declList_;
 };
 
+// Used for OpenMP DECLARE MAPPER, it holds the declaration constructs
+// so they can be serialized into module files and later re-parsed when
+// USE-associated.
+class MapperDetails {
+public:
+  using DeclVector = std::vector<const parser::OpenMPDeclarativeConstruct *>;
+
+  MapperDetails() = default;
+
+  void AddDecl(const parser::OpenMPDeclarativeConstruct *decl) {
+    declList_.emplace_back(decl);
+  }
+  const DeclVector &GetDeclList() const { return declList_; }
+
+private:
+  DeclVector declList_;
+};
+
 class UnknownDetails {};
 
 using Details = std::variant<UnknownDetails, MainProgramDetails, ModuleDetails,
     SubprogramDetails, SubprogramNameDetails, EntityDetails,
     ObjectEntityDetails, ProcEntityDetails, AssocEntityDetails,
     DerivedTypeDetails, UseDetails, UseErrorDetails, HostAssocDetails,
     GenericDetails, ProcBindingDetails, NamelistDetails, CommonBlockDetails,
-    TypeParamDetails, MiscDetails, UserReductionDetails>;
+    TypeParamDetails, MiscDetails, UserReductionDetails, MapperDetails>;
 llvm::raw_ostream &operator<<(llvm::raw_ostream &, const Details &);
 std::string DetailsToString(const Details &);
 

flang/lib/Lower/Bridge.cpp

@@ -447,6 +447,13 @@ class FirConverter : public Fortran::lower::AbstractConverter {
       }
     });
 
+    // 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); });

flang/lib/Lower/OpenMP/ClauseProcessor.cpp

@@ -1402,10 +1402,14 @@ 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,

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),
+  // 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,
@@ -4239,3 +4255,32 @@ 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;
+
+  // 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);
+        }
+      }
+    }
+  }
+}

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());
@@ -1098,6 +1100,16 @@ 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()) {