[flang-commits] [flang] [flang][OpenMP] Fix mapping of constant arrays. (PR #176763)
Abid Qadeer via flang-commits
flang-commits at lists.llvm.org
Mon Jan 19 07:14:22 PST 2026
https://github.com/abidh created https://github.com/llvm/llvm-project/pull/176763
The compiler skips mapping of named constants (parameters) to OpenMP target regions under the assumption that constants don't need to be mapped. This assumption is not valid when array is accessed inside with dynamic index. The problem can be seen with the following code:
```
module fir_lowering_check
implicit none
integer, parameter :: dp = selected_real_kind(15, 307)
real(dp), parameter :: arrays(2) = (/ 0.0, 0.0 /)
contains
subroutine test(hold)
integer, intent(in) :: hold
integer :: z
real(dp) :: temp
!$omp target teams distribute parallel do
do z = 1, 2
temp = arrays(hold)
end do
!$omp end target teams distribute parallel do
end subroutine test
end module fir_lowering_check
program main
use fir_lowering_check
implicit none
integer :: hold
hold = 1
call test(hold)
print *, "Finished"
end program main
```
It fails with the following error
`'hlfir.designate' op using value defined outside the region`
The fix is to allow mapping of constant arrays and map them as `to`.
>From ff7e5013ba0f238932af99b30d0aef9b660bac80 Mon Sep 17 00:00:00 2001
From: Abid Qadeer <haqadeer at amd.com>
Date: Mon, 19 Jan 2026 14:51:56 +0000
Subject: [PATCH] [flang][OpenMP] Fix mapping of constant arrays.
The compiler skips mapping of named constants (parameters) to OpenMP
target regions under the assumption that constants don't need to be
mapped. This assumption is not valid when array is accessed inside with
dynamic index. The problem can be seen with the following code:
`module fir_lowering_check
implicit none
integer, parameter :: dp = selected_real_kind(15, 307)
real(dp), parameter :: arrays(2) = (/ 0.0, 0.0 /)
contains
subroutine s_compute_chemistry_reaction_flux(hold)
integer, intent(in) :: hold
integer :: z
real(dp) :: temp
!$omp target teams distribute parallel do
do z = 1, 2
temp = arrays(hold)
end do
!$omp end target teams distribute parallel do
end subroutine s_compute_chemistry_reaction_flux
end module fir_lowering_check
program fir_mvp_prog
use fir_lowering_check
implicit none
integer :: hold
hold = 1
call s_compute_chemistry_reaction_flux(hold)
print *, "Finished"
end program fir_mvp_prog`
It fails with the following error
"'hlfir.designate' op using value defined outside the region"
The fix is to allow mapping of constant arrays and map them as "to".
---
flang/lib/Lower/OpenMP/OpenMP.cpp | 11 +++-
.../Lower/OpenMP/target-parameter-array.f90 | 60 +++++++++++++++++++
2 files changed, 69 insertions(+), 2 deletions(-)
create mode 100644 flang/test/Lower/OpenMP/target-parameter-array.f90
diff --git a/flang/lib/Lower/OpenMP/OpenMP.cpp b/flang/lib/Lower/OpenMP/OpenMP.cpp
index 0764693f748a5..dddb02adffa36 100644
--- a/flang/lib/Lower/OpenMP/OpenMP.cpp
+++ b/flang/lib/Lower/OpenMP/OpenMP.cpp
@@ -995,6 +995,11 @@ getImplicitMapTypeAndKind(fir::FirOpBuilder &firOpBuilder,
} else {
mapFlag |= mlir::omp::ClauseMapFlags::to;
}
+ } else if (semantics::IsNamedConstant(sym)) {
+ // Parameter constants should be mapped as read-only (to) since they
+ // cannot be modified. Mapping them as tofrom would cause a crash when
+ // trying to write back to read-only memory.
+ mapFlag |= mlir::omp::ClauseMapFlags::to;
} else if (!fir::isa_builtin_cptr_type(varType)) {
mapFlag |= mlir::omp::ClauseMapFlags::to;
mapFlag |= mlir::omp::ClauseMapFlags::from;
@@ -2657,8 +2662,10 @@ genTargetOp(lower::AbstractConverter &converter, lower::SymMap &symTable,
if (!converter.getSymbolAddress(sym))
return;
- // Skip parameters/constants as they do not need to be mapped.
- if (semantics::IsNamedConstant(sym))
+ // Skip scalar parameters/constants as they do not need to be mapped.
+ // However, parameter arrays must be mapped as they may be accessed with
+ // dynamic indices on the device (e.g., const_array(runtime_index)).
+ if (semantics::IsNamedConstant(sym) && sym.Rank() == 0)
return;
if (!isDuplicateMappedSymbol(sym, dsp.getAllSymbolsToPrivatize(),
diff --git a/flang/test/Lower/OpenMP/target-parameter-array.f90 b/flang/test/Lower/OpenMP/target-parameter-array.f90
new file mode 100644
index 0000000000000..f494a6d479370
--- /dev/null
+++ b/flang/test/Lower/OpenMP/target-parameter-array.f90
@@ -0,0 +1,60 @@
+! RUN: %flang_fc1 -emit-hlfir -fopenmp %s -o - | FileCheck %s
+
+! Test that parameter (constant) arrays can be mapped to OpenMP target regions
+! and are mapped as read-only when accessed with dynamic indices.
+
+module param_array_module
+ implicit none
+ integer, parameter :: dp = selected_real_kind(15, 307)
+
+ ! Parameter arrays that should be mapped to device
+ real(dp), parameter :: const_array(3) = [1.0_dp, 2.0_dp, 3.0_dp]
+ integer, parameter :: int_array(4) = [10, 20, 30, 40]
+
+contains
+
+! Test 1: Parameter array with dynamic index in target region with teams distribute
+! CHECK-LABEL: func.func @_QMparam_array_modulePtest_param_array_target
+subroutine test_param_array_target(idx)
+ integer, intent(in) :: idx
+ integer :: i
+ real(dp) :: result
+
+ ! CHECK: omp.map.info{{.*}}map_clauses(implicit, to){{.*}}{name = "const_array"}
+ !$omp target teams distribute parallel do
+ do i = 1, 3
+ ! Access parameter array with dynamic index
+ result = const_array(idx)
+ end do
+ !$omp end target teams distribute parallel do
+
+end subroutine test_param_array_target
+
+! Integer parameter array in simple target region
+! CHECK-LABEL: func.func @_QMparam_array_modulePtest_int_param_array
+subroutine test_int_param_array(idx)
+ integer, intent(in) :: idx
+ integer :: result
+
+ ! CHECK: omp.map.info{{.*}}map_clauses(implicit, to){{.*}}{name = "int_array"}
+ !$omp target
+ ! Access parameter array with dynamic index
+ result = int_array(idx)
+ !$omp end target
+
+end subroutine test_int_param_array
+
+! Verify scalar parameters are NOT mapped (can be inlined)
+! CHECK-LABEL: func.func @_QMparam_array_modulePtest_scalar_param
+subroutine test_scalar_param()
+ integer, parameter :: scalar_const = 42
+ integer :: result
+
+ ! CHECK-NOT: omp.map.info{{.*}}{name = "scalar_const"}
+ !$omp target
+ result = scalar_const
+ !$omp end target
+
+end subroutine test_scalar_param
+
+end module param_array_module
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