[flang] Retrieve the correct scope when lowering SELECT TYPE

[clementval]

Summary

Scope to retrieve the associating entity is needed to map the
symbol to the IR value. The scope can be found with a source
information. For the type case in SELECT TYPE construct, the source
information is on the Statement<TypeCase>. This patch updates
the lowering so the scopes for each type guards is retrieved
before the processing.

[PeteSteinfeld]

All builds and tests correctly and looks good.

[vdonaldson]

So you need to drop down a scope level - looks ok to me.

flang/lib/Lower/Bridge.cpp

void genFIR(const Fortran::parser::SelectTypeConstruct &selectTypeConstruct) {
     mlir::MLIRContext *context = builder->getContext();
     Fortran::lower::StatementContext stmtCtx;
     fir::ExtendedValue selector;
     llvm::SmallVector<mlir::Attribute> attrList;
     llvm::SmallVector<mlir::Block *> blockList;
     unsigned typeGuardIdx = 0;
     std::size_t defaultAttrPos = std::numeric_limits<size_t>::max();
     bool hasLocalScope = false;
+    llvm::SmallVector<const Fortran::semantics::Scope *> typeCaseScopes;
+
+    const auto &typeCaseList =
+        std::get<std::list<Fortran::parser::SelectTypeConstruct::TypeCase>>(
+            selectTypeConstruct.t);
+    for (const auto &typeCase : typeCaseList) {
+      const auto &stmt =
+          std::get<Fortran::parser::Statement<Fortran::parser::TypeGuardStmt>>(
+              typeCase.t);
+      const Fortran::semantics::Scope &scope =
+          bridge.getSemanticsContext().FindScope(stmt.source);
+      typeCaseScopes.push_back(&scope);
+    }
 
     for (Fortran::lower::pft::Evaluation &eval :
          getEval().getNestedEvaluations()) {
       if (auto *selectTypeStmt =
               eval.getIf<Fortran::parser::SelectTypeStmt>()) {
         // A genFIR(SelectTypeStmt) call would have unwanted side effects.
         maybeStartBlock(eval.block);
         // Retrieve the selector
for (Fortran::lower::pft::Evaluation &eval :
         if (hasLocalScope)
           localSymbols.popScope();
         localSymbols.pushScope();
         hasLocalScope = true;
         assert(attrList.size() >= typeGuardIdx &&
                "TypeGuard attribute missing");
         mlir::Attribute typeGuardAttr = attrList[typeGuardIdx];
         mlir::Block *typeGuardBlock = blockList[typeGuardIdx];
-        const Fortran::semantics::Scope &guardScope =
-            bridge.getSemanticsContext().FindScope(eval.position);
         mlir::OpBuilder::InsertPoint crtInsPt = builder->saveInsertionPoint();
         builder->setInsertionPointToStart(typeGuardBlock);
 
         auto addAssocEntitySymbol = [&](fir::ExtendedValue exv) {
-          for (auto &symbol : guardScope.GetSymbols()) {
+          for (auto &symbol : typeCaseScopes[typeGuardIdx]->GetSymbols()) {
             if (symbol->GetUltimate()
                     .detailsIf<Fortran::semantics::AssocEntityDetails>()) {
               addSymbol(symbol, exv);
               break;
             }
           }
         };
 

flang/test/Lower/select-type.f90

 ! CHECK: ^bb2:
 ! CHECK: ^bb3:
 ! CHECK: fir.select_type %{{.*}} : !fir.class<!fir.array<?x!fir.type<_QMselect_type_lower_testTp1{a:i32,b:i32}>>> [#fir.type_is<!fir.type<_QMselect_type_lower_testTp1{a:i32,b:i32}>>, ^bb4, #fir.class_is<!fir.type<_QMselect_type_lower_testTp1{a:i32,b:i32}>>, ^bb6, unit, ^bb5]
 ! CHECK: ^bb4:
 ! CHECK: ^bb5:
 ! CHECK: ^bb6:
 ! CHECK: ^bb7:
 
+  subroutine select_type14(a, b)
+    class(p1) :: a, b
+
+    select type(a)
+      type is (p2)
+        select type (b)
+          type is (p2)
+            print*,a%c,b%C
+        end select
+      class default
+        print*,a%a
+    end select
+  end subroutine
+
+  ! Just makes sure the example can be lowered.
+  ! CHECK-LABEL: func.func @_QMselect_type_lower_testPselect_type14
+   
 end module
 
 program test_select_type
   use select_type_lower_test
 
   integer :: a
   integer :: arr(2)
   real :: b