[flang][openacc] Lower if_present clause correctly on acc update

The `if_present` clause is modeled as an attribute on the
acc.update operation. The lowering was not adding correctly the attribute
when the clause was present. This patch update the lowering to add
the attribute when needed.

Reviewed By: razvanlupusoru

Differential Revision: https://reviews.llvm.org/D150171

flang/lib/Lower/OpenACC.cpp

@@ -1481,6 +1481,8 @@ genACCUpdateOp(Fortran::lower::AbstractConverter &converter,
       genDataOperandOperations<mlir::acc::UpdateDeviceOp>(
           deviceClause->v, converter, semanticsContext, stmtCtx,
           dataClauseOperands, mlir::acc::DataClause::acc_update_device, false);
+    } else if (std::get_if<Fortran::parser::AccClause::IfPresent>(&clause.u)) {
+      addIfPresentAttr = true;
     }
   }
 

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

@@ -14,6 +14,11 @@ subroutine acc_update
   !$acc update host(a)
 ! CHECK: %[[DEVPTR_A:.*]] = acc.getdeviceptr varPtr(%[[A]] : !fir.ref<!fir.array<10x10xf32>>) bounds(%{{.*}}, %{{.*}}) -> !fir.ref<!fir.array<10x10xf32>> {dataClause = 17 : i64, name = "a", structured = false}
 ! CHECK: acc.update dataOperands(%[[DEVPTR_A]] : !fir.ref<!fir.array<10x10xf32>>){{$}}
+! CHECK: acc.update_host accPtr(%[[DEVPTR_A]] : !fir.ref<!fir.array<10x10xf32>>) bounds(%{{.*}}, %{{.*}}) to varPtr(%[[A]] : !fir.ref<!fir.array<10x10xf32>>) {name = "a", structured = false}
+
+  !$acc update host(a) if_present
+! CHECK: %[[DEVPTR_A:.*]] = acc.getdeviceptr varPtr(%[[A]] : !fir.ref<!fir.array<10x10xf32>>) bounds(%{{.*}}, %{{.*}}) -> !fir.ref<!fir.array<10x10xf32>> {dataClause = 17 : i64, name = "a", structured = false}
+! CHECK: acc.update dataOperands(%[[DEVPTR_A]] : !fir.ref<!fir.array<10x10xf32>>) attributes {ifPresent}{{$}}
 ! CHECK: acc.update_host accPtr(%[[DEVPTR_A]] : !fir.ref<!fir.array<10x10xf32>>) bounds(%{{.*}}, %{{.*}}) to varPtr(%[[A]] : !fir.ref<!fir.array<10x10xf32>>) {name = "a", structured = false}
 
   !$acc update host(a) if(.true.)