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

[clementval]

Summary

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.

flang/lib/Lower/OpenACC.cpp

if (const auto *ifClause =
       genDataOperandOperations<mlir::acc::GetDevicePtrOp>(
           hostClause->v, converter, semanticsContext, stmtCtx,
           updateHostOperands, mlir::acc::DataClause::acc_update_host, false);
     } else if (const auto *deviceClause =
                    std::get_if<Fortran::parser::AccClause::Device>(&clause.u)) {
       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;
     }
   }
 
   dataClauseOperands.append(updateHostOperands);
 
   // Prepare the operand segment size attribute and the operands value range.
   llvm::SmallVector<mlir::Value> operands;
   llvm::SmallVector<int32_t> operandSegments;

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

 !CHECK: %[[B:.*]] = fir.alloca !fir.array<10x10xf32> {{{.*}}uniq_name = "{{.*}}Eb"}
 !CHECK: %[[C:.*]] = fir.alloca !fir.array<10x10xf32> {{{.*}}uniq_name = "{{.*}}Ec"}
 
   !$acc update host(a)
 ! CHECK: %[[DEVPTR_A:.*]] = acc.getdeviceptr varPtr(%[[A]] : !fir.ref<!fir.array<10x10xf32>>) bounds(%{{.*}}, %{{.*}}) -> !fir.ref<!fir.array<10x10xf32>> {dataClause = 17 : i64, name = "a", structured = false}
 ! CHECK: acc.update dataOperands(%[[DEVPTR_A]] : !fir.ref<!fir.array<10x10xf32>>){{$}}
 ! 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}
+
   !$acc update host(a) if(.true.)
 ! CHECK: %[[DEVPTR_A:.*]] = acc.getdeviceptr varPtr(%[[A]] : !fir.ref<!fir.array<10x10xf32>>) bounds(%{{.*}}, %{{.*}}) -> !fir.ref<!fir.array<10x10xf32>> {dataClause = 17 : i64, name = "a", structured = false}
 ! CHECK: %[[IF1:.*]] = arith.constant true
 ! CHECK: acc.update if(%[[IF1]]) dataOperands(%[[DEVPTR_A]] : !fir.ref<!fir.array<10x10xf32>>){{$}}
 ! 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(ifCondition)
 ! 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}