[flang][openacc] Add lowering support for the link clause on OpenACC declare

[clementval]

Summary

Lower link clause with data entry operation.

[razvanlupusoru]

Seems OK to me!

flang/lib/Lower/OpenACC.cpp

for (const Fortran::parser::AccClause &clause : accClauseList.v) {
     } else if (const auto *deviceResidentClause =
                    std::get_if<Fortran::parser::AccClause::DeviceResident>(
                        &clause.u)) {
       genDataOperandOperations<mlir::acc::DeclareDeviceResidentOp>(
           deviceResidentClause->v, converter, semanticsContext, stmtCtx,
           dataClauseOperands,
           mlir::acc::DataClause::acc_declare_device_resident,
           /*structured=*/true);
+    } else if (const auto *linkClause =
+                   std::get_if<Fortran::parser::AccClause::Link>(&clause.u)) {
+      genDataOperandOperations<mlir::acc::DeclareLinkOp>(
+          linkClause->v, converter, semanticsContext, stmtCtx,
+          dataClauseOperands, mlir::acc::DataClause::acc_declare_link,
+          /*structured=*/true);
     } else {
       mlir::Location clauseLocation = converter.genLocation(clause.source);
       TODO(clauseLocation, "clause on declare directive");
     }
   }
   builder.create<mlir::acc::DeclareEnterOp>(loc, dataClauseOperands);
 
   if (!createEntryOperands.empty() || !copyEntryOperands.empty() ||

flang/test/Lower/OpenACC/acc-declare.f90

 
 ! CHECK-LABEL: func.func @_QMacc_declarePacc_declare_device_resident(
 ! CHECK-SAME: %[[ARG0:.*]]: !fir.ref<!fir.array<100xi32>> {fir.bindc_name = "a"})
 ! CHECK: %[[DEVICERES:.*]] = acc.declare_device_resident varPtr(%[[ARG0]] : !fir.ref<!fir.array<100xi32>>) bounds(%{{.*}}) -> !fir.ref<!fir.array<100xi32>> {name = "a"}
 ! CHECK: acc.declare_enter dataOperands(%[[DEVICERES]] : !fir.ref<!fir.array<100xi32>>)
 ! CHECK: %{{.*}}:2 = fir.do_loop %{{.*}} = %{{.*}} to %{{.*}} step %{{.*}} iter_args(%arg{{.*}} = %{{.*}}) -> (index, i32)
 ! CHECK-NOT: acc.declare_exit
 
+  subroutine acc_declare_link(a)
+    integer :: a(100), i
+    !$acc declare link(a)
+
+    do i = 1, 100
+      a(i) = i
+    end do
+  end subroutine
+
+! CHECK-LABEL: func.func @_QMacc_declarePacc_declare_link(
+! CHECK-SAME: %[[ARG0:.*]]: !fir.ref<!fir.array<100xi32>> {fir.bindc_name = "a"})
+! CHECK: %[[LINK:.*]] = acc.declare_link varPtr(%[[ARG0]] : !fir.ref<!fir.array<100xi32>>) bounds(%{{.*}}) -> !fir.ref<!fir.array<100xi32>> {name = "a"}
+! CHECK: acc.declare_enter dataOperands(%[[LINK]] : !fir.ref<!fir.array<100xi32>>)
+! CHECK: %{{.*}}:2 = fir.do_loop %{{.*}} = %{{.*}} to %{{.*}} step %{{.*}} iter_args(%arg{{.*}} = %{{.*}}) -> (index, i32)
+! CHECK-NOT: acc.declare_exit
+
 end module