[flang][OpenMP] Put taskgroup in a new scope

Although taskgroup is a privatizing construct, because of
task_reduction clause, a new scope was not being created for it.
This could cause an extra privatization of variables when
taskgroup was lowered, because its scope would be the same as of
the parent privatizing construct.

This fixes regressions in tests 1052_0201 and 1052_0205, from
Fujitsu testsuite.

This issue didn't happen before because implicit symbols were
being created in a different way before #142154.

Author: luporl

flang/lib/Semantics/resolve-names.cpp

@@ -1729,7 +1729,6 @@ bool OmpVisitor::NeedsScope(const parser::OpenMPBlockConstruct &x) {
   switch (beginDir.v) {
   case llvm::omp::Directive::OMPD_master:
   case llvm::omp::Directive::OMPD_ordered:
-  case llvm::omp::Directive::OMPD_taskgroup:
     return false;
   default:
     return true;

flang/test/Lower/OpenMP/taskgroup02.f90

@@ -0,0 +1,32 @@
+! RUN: %flang_fc1 -emit-hlfir -fopenmp -o - %s 2>&1 | FileCheck %s
+
+! Check that variables are not privatized twice when TASKGROUP is used.
+
+!CHECK-LABEL: func.func @_QPsub() {
+!CHECK:         omp.parallel {
+!CHECK:           %[[PAR_I:.*]]:2 = hlfir.declare %{{.*}} {uniq_name = "_QFsubEi"}
+!CHECK:           omp.master {
+!CHECK:             omp.taskgroup {
+!CHECK-NEXT:          omp.task private(@_QFsubEi_firstprivate_i32 %[[PAR_I]]#0 -> %[[TASK_I:.*]] : !fir.ref<i32>) {
+!CHECK:                 %[[TASK_I_DECL:.*]]:2 = hlfir.declare %[[TASK_I]] {uniq_name = "_QFsubEi"}
+!CHECK:               }
+!CHECK:             }
+!CHECK:           }
+!CHECK:         }
+
+subroutine sub()
+  integer, dimension(10) :: a
+  integer :: i
+
+  !$omp parallel
+    !$omp master
+      do i=1,10
+       !$omp taskgroup
+         !$omp task shared(a)
+           a(i) = 1
+         !$omp end task
+       !$omp end taskgroup
+      end do
+    !$omp end master
+  !$omp end parallel
+end subroutine