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

[clementval]

Summary

Lower the present clause on the OpenACC declare construct in
function/subroutine.

Depends on D156572

[razvanlupusoru]

Looks great. I do think eventually it might be good to introduce an opposite for "present", but seems fine like this for now!

flang/lib/Lower/OpenACC.cpp

static Op createDataEntryOp(fir::FirOpBuilder &builder, mlir::Location loc,
   op->setAttr(Op::getOperandSegmentSizeAttr(),
               builder.getDenseI32ArrayAttr(
                   {1, varPtrPtr ? 1 : 0, static_cast<int32_t>(bounds.size())}));
   return op;
 }
 
 static void addDeclareAttr(fir::FirOpBuilder &builder, mlir::Operation *op,
                            mlir::acc::DataClause clause) {
+  if (!op)
+    return;
   op->setAttr(mlir::acc::getDeclareAttrName(),
               mlir::acc::DeclareAttr::get(builder.getContext(),
                                           mlir::acc::DataClauseAttr::get(
                                               builder.getContext(), clause)));
 }
 
 template <typename Op>
 static void
if (const auto *copyClause =
           std::get<Fortran::parser::AccObjectList>(listWithModifier.t);
       auto crtDataStart = dataClauseOperands.size();
       genDataOperandOperations<mlir::acc::CreateOp>(
           accObjectList, converter, semanticsContext, stmtCtx,
           dataClauseOperands, mlir::acc::DataClause::acc_create,
           /*structured=*/true, /*setDeclareAttr=*/true);
       createEntryOperands.append(dataClauseOperands.begin() + crtDataStart,
                                  dataClauseOperands.end());
+    } else if (const auto *presentClause =
+                   std::get_if<Fortran::parser::AccClause::Present>(
+                       &clause.u)) {
+      genDataOperandOperations<mlir::acc::PresentOp>(
+          presentClause->v, converter, semanticsContext, stmtCtx,
+          dataClauseOperands, mlir::acc::DataClause::acc_present,
+          /*structured=*/true, /*setDeclareAttr=*/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()) {
     // Attach declare exit operation generation to function context.
-  fctCtx.attachCleanup([&builder, loc, dataClauseOperands, createEntryOperands,
-                        copyEntryOperands]() {
+    fctCtx.attachCleanup([&builder, loc, dataClauseOperands,
+                          createEntryOperands, copyEntryOperands]() {
       builder.create<mlir::acc::DeclareExitOp>(loc, dataClauseOperands);
       genDataExitOperations<mlir::acc::CreateOp, mlir::acc::DeleteOp>(
-        builder, createEntryOperands, /*structured=*/true, /*implicit=*/false);
-    genDataExitOperations<mlir::acc::CopyinOp, mlir::acc::CopyoutOp>(builder,
-        copyEntryOperands, /*structured=*/true, /*implicit=*/false);
+          builder, createEntryOperands, /*structured=*/true,
+          /*implicit=*/false);
+      genDataExitOperations<mlir::acc::CopyinOp, mlir::acc::CopyoutOp>(
+          builder, copyEntryOperands, /*structured=*/true, /*implicit=*/false);
     });
   }
+}
 
 static void
 genDeclareInModule(Fortran::lower::AbstractConverter &converter,
                    mlir::ModuleOp &moduleOp,
                    const Fortran::parser::AccClauseList &accClauseList) {
   mlir::OpBuilder modBuilder(moduleOp.getBodyRegion());
   for (const Fortran::parser::AccClause &clause : accClauseList.v) {
     if (const auto *createClause =

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

 
 ! CHECK: %{{.*}}:2 = fir.do_loop %{{.*}} = %{{.*}} to %{{.*}} step %{{.*}} iter_args(%{{.*}} = %{{.*}}) -> (index, i32) {
 ! CHECK: }
 
 ! CHECK: acc.declare_exit dataOperands(%[[CREATE]] : !fir.ref<!fir.array<100xi32>>)
 ! CHECK: acc.delete accPtr(%[[CREATE]] : !fir.ref<!fir.array<100xi32>>) bounds(%[[BOUND]]) {dataClause = #acc<data_clause acc_create>, name = "a"}
 ! CHECK: return
 
+  subroutine acc_declare_present(a)
+    integer :: a(100), i
+    !$acc declare present(a)
+
+    do i = 1, 100
+      a(i) = i
+    end do
+  end subroutine
+
+! CHECK-LABEL: func.func @_QMacc_declarePacc_declare_present(
+! CHECK-SAME: %[[ARG0:.*]]: !fir.ref<!fir.array<100xi32>> {fir.bindc_name = "a"})
+! CHECK: %[[BOUND:.*]] = acc.bounds lowerbound(%{{.*}} : index) upperbound(%{{.*}} : index) extent(%{{.*}} : index) stride(%{{.*}} : index) startIdx(%c1 : index)
+! CHECK: %[[PRESENT:.*]] = acc.present varPtr(%[[ARG0]] : !fir.ref<!fir.array<100xi32>>) bounds(%[[BOUND]]) -> !fir.ref<!fir.array<100xi32>> {name = "a"}
+! CHECK: acc.declare_enter dataOperands(%[[PRESENT]] : !fir.ref<!fir.array<100xi32>>)
+! CHECK: %{{.*}}:2 = fir.do_loop %{{.*}} = %{{.*}} to %{{.*}} step %{{.*}} iter_args(%arg{{.*}} = %{{.*}}) -> (index, i32)
+! CHECK-NOT: acc.declare_exit
 
 end module