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[flang][cuda] Move function result assignment to managed variable on host #163705

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Merged
merged 1 commit into from
Oct 16, 2025
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[flang][cuda] Move function result assignment to managed variable on host #163705

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10 changes: 6 additions & 4 deletions flang/include/flang/Evaluate/tools.h
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Original file line number Diff line number Diff line change
Expand Up @@ -1342,10 +1342,12 @@ inline bool IsCUDADataTransfer(const A &lhs, const B &rhs) {
int rhsNbManagedSymbols = {GetNbOfCUDAManagedOrUnifiedSymbols(rhs)};
int rhsNbSymbols{GetNbOfCUDADeviceSymbols(rhs)};

// Special case where only managed or unifed symbols are involved. This is
// performed on the host.
if (lhsNbManagedSymbols == 1 && rhsNbManagedSymbols == 1 &&
rhsNbSymbols == 1) {
// Special cases perforemd on the host:
// - Only managed or unifed symbols are involved on RHS and LHS.
// - LHS is managed or unified and the RHS is host only.
if ((lhsNbManagedSymbols == 1 && rhsNbManagedSymbols == 1 &&
rhsNbSymbols == 1) ||
(lhsNbManagedSymbols == 1 && rhsNbSymbols == 0)) {
return false;
}
return HasCUDADeviceAttrs(lhs) || rhsNbSymbols > 0;
Expand Down
20 changes: 20 additions & 0 deletions flang/test/Lower/CUDA/cuda-data-transfer.cuf
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Expand Up @@ -15,6 +15,13 @@ module mod1

real(kind=8), device, allocatable, dimension(:) :: p

interface
function __sum(a_d) result(res_h)
integer(4), managed, intent(in) :: a_d(:,:,:,:)
integer(4), allocatable, managed :: res_h(:,:,:)
end function
end interface

contains
function dev1(a)
integer, device :: a(:)
Expand Down Expand Up @@ -522,3 +529,16 @@ end subroutine
! CHECK: hlfir.yield_element %[[CONV]] : f32
! CHECK: }
! CHECKL: hlfir.assign %[[ELE]] to %[[HD]]#0 : !hlfir.expr<10x20x30xf32>, !fir.ref<!fir.array<10x20x30xf32>>

subroutine sub28(N1,N2,N3,N4)
use mod1
integer(4), managed :: a(N1,N2,N3,N4)
integer(4), managed :: bres(N1,N2,N3)
bres = __sum(a)
end subroutine

! CHECK-LABEL: func.func @_QPsub28
! CHECK: fir.call @_QP__sum
! CHECK-NOT: cuf.data_transfer
! CHECK: hlfir.assign
! CHECK-NOT: cuf.data_transfer
20 changes: 8 additions & 12 deletions flang/test/Lower/CUDA/cuda-managed.cuf
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@@ -1,27 +1,23 @@
! RUN: bbc -emit-hlfir -fcuda %s -o - | FileCheck %s

! Check for implicit data transfer of managed variable

subroutine testr2(N1,N2)
real(4), managed :: ai4(N1,N2)
real(4), allocatable :: bRefi4(:)

integer :: i1, i2

do i2 = 1, N2
do i1 = 1, N1
ai4(i1,i2) = i1 + N1*(i2-1)
enddo
enddo

allocate(bRefi4 (N1))
allocate(bRefi4(N1))
do i1 = 1, N1
bRefi4(i1) = (ai4(i1,1)+ai4(i1,N2))*N2/2
enddo
deallocate(bRefi4)

end subroutine

!CHECK-LABEL: func.func @_QPtestr2
!CHECK: %[[ALLOC:.*]] = cuf.alloc !fir.array<?x?xf32>, %{{.*}}, %{{.*}} : index, index {bindc_name = "ai4", data_attr = #cuf.cuda<managed>, uniq_name = "_QFtestr2Eai4"} -> !fir.ref<!fir.array<?x?xf32>>
!CHECK: %[[DECLARE:.*]]:2 = hlfir.declare %[[ALLOC]](%{{.*}}) {data_attr = #cuf.cuda<managed>, uniq_name = "_QFtestr2Eai4"} : (!fir.ref<!fir.array<?x?xf32>>, !fir.shape<2>) -> (!fir.box<!fir.array<?x?xf32>>, !fir.ref<!fir.array<?x?xf32>>)
!CHECK: %[[DEST:.*]] = hlfir.designate %[[DECLARE]]#0 (%{{.*}}, %{{.*}}) : (!fir.box<!fir.array<?x?xf32>>, i64, i64) -> !fir.ref<f32>
!CHECK: cuf.data_transfer %{{.*}}#0 to %[[DEST]] {transfer_kind = #cuf.cuda_transfer<host_device>} : !fir.ref<f32>, !fir.ref<f32>
! CHECK-LABEL: func.func @_QPtestr2
! CHECK: %[[MANAGED:.*]]:2 = hlfir.declare %22(%23) {data_attr = #cuf.cuda<managed>, uniq_name = "_QFtestr2Eai4"} : (!fir.ref<!fir.array<?x?xf32>>, !fir.shape<2>) -> (!fir.box<!fir.array<?x?xf32>>, !fir.ref<!fir.array<?x?xf32>>)
! CHECK: %[[TMP:.*]] = fir.allocmem !fir.array<?x?xf32>, %16, %21 {bindc_name = ".tmp", uniq_name = ""}
! CHECK: %[[TMP_DECL:.*]]:2 = hlfir.declare %[[TMP]](%{{.*}}) {uniq_name = ".tmp"} : (!fir.heap<!fir.array<?x?xf32>>, !fir.shape<2>) -> (!fir.box<!fir.array<?x?xf32>>, !fir.heap<!fir.array<?x?xf32>>)
! CHECK: cuf.data_transfer %[[MANAGED]]#1 to %[[TMP_DECL]]#0 {transfer_kind = #cuf.cuda_transfer<device_host>} : !fir.ref<!fir.array<?x?xf32>>, !fir.box<!fir.array<?x?xf32>>