[flang-commits] [flang] [flang][OpenMP] Don't emit implicit default mapper for flat allocatable derived types (PR #209645)
Spencer Bryngelson via flang-commits
flang-commits at lists.llvm.org
Wed Jul 22 07:25:02 PDT 2026
https://github.com/sbryngelson updated https://github.com/llvm/llvm-project/pull/209645
>From 4a2ba7805145e2d96d217e8de7853d73cc2ad3b7 Mon Sep 17 00:00:00 2001
From: Spencer Bryngelson <sbryngelson at gmail.com>
Date: Tue, 14 Jul 2026 17:18:44 -0500
Subject: [PATCH] [flang][OpenMP] Don't emit implicit default mapper for flat
allocatable derived types
An allocatable/pointer capture of a derived type triggered synthesis of an
implicit default declare mapper unconditionally. For a flat type -- all
components trivially mappable, no allocatable/pointer/nested-record members --
that mapper is unnecessary: the object maps as a plain bulk copy. Emitting it
anyway lowers to a per-element, per-component mapper walk in the offload
runtime with O(num_elements * num_components) cost, busy-looping the host for
minutes on large device-resident arrays while the GPU sits idle
(ROCm/llvm-project#3385).
requiresImplicitDefaultDeclareMapper() already answers whether a type needs a
mapper; the allocatable-capture path never consulted it. Gate on it. Pointer
captures and user/pre-existing declare mappers are unaffected.
Update derived-type-map.f90 and defaultmap.f90, which asserted a mapper for a
flat allocatable capture, and add implicit-map-flat-allocatable-no-mapper.f90.
Assisted-by: Claude (Opus 4.8)
---
flang/lib/Lower/OpenMP/OpenMP.cpp | 8 ++++++-
flang/test/Lower/OpenMP/defaultmap.f90 | 5 +++-
flang/test/Lower/OpenMP/derived-type-map.f90 | 4 ++--
...mplicit-map-flat-allocatable-no-mapper.f90 | 23 +++++++++++++++++++
...implicit-map-pointer-no-default-mapper.f90 | 2 ++
5 files changed, 38 insertions(+), 4 deletions(-)
create mode 100644 flang/test/Lower/OpenMP/implicit-map-flat-allocatable-no-mapper.f90
diff --git a/flang/lib/Lower/OpenMP/OpenMP.cpp b/flang/lib/Lower/OpenMP/OpenMP.cpp
index a3acc2e991307..e2a2e54ac2783 100644
--- a/flang/lib/Lower/OpenMP/OpenMP.cpp
+++ b/flang/lib/Lower/OpenMP/OpenMP.cpp
@@ -3999,7 +3999,13 @@ genTargetOp(lower::AbstractConverter &converter, lower::SymMap &symTable,
// Avoid attaching implicit default mappers to pointer captures.
// For large pointer-based derived aggregates this can over-map
// nested payloads and conflict with explicit enter/exit maps.
- if (!isPointer && (hasDefaultMapper || isAllocatable)) {
+ //
+ // For an allocatable capture, only synthesize an implicit default
+ // mapper when the type requires one; a flat record does not.
+ if (!isPointer &&
+ (hasDefaultMapper ||
+ (isAllocatable &&
+ requiresImplicitDefaultDeclareMapper(*typeSpec)))) {
if (!hasDefaultMapper) {
if (auto recordType = mlir::dyn_cast_or_null<fir::RecordType>(
converter.genType(*typeSpec)))
diff --git a/flang/test/Lower/OpenMP/defaultmap.f90 b/flang/test/Lower/OpenMP/defaultmap.f90
index d2c9b48b13834..d43efdb3ad8ed 100644
--- a/flang/test/Lower/OpenMP/defaultmap.f90
+++ b/flang/test/Lower/OpenMP/defaultmap.f90
@@ -1,6 +1,9 @@
!RUN: %flang_fc1 -emit-hlfir -fopenmp -fopenmp-version=52 -mmlir --enable-delayed-privatization-staging=false %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-NO-FPRIV
!RUN: %flang_fc1 -emit-hlfir -fopenmp -fopenmp-version=52 -mmlir --enable-delayed-privatization-staging=true %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-FPRIV
+! Flat derived types get no implicit default mapper through an allocatable.
+! CHECK-NOT: omp.declare_mapper
+
subroutine defaultmap_allocatable_present()
implicit none
integer, dimension(:), allocatable :: arr
@@ -117,7 +120,7 @@ subroutine defaultmap_scalar_implicit_mapper()
type(dtype), allocatable :: obj
! CHECK-LABEL: func.func @_QPdefaultmap_scalar_implicit_mapper
-! CHECK: %[[BASE_MAP:.*]] = omp.map.info {{.*}} map_clauses(implicit, tofrom) capture(ByRef) {{.*}} mapper(@{{.*}}) -> {{.*}} {name = ""}
+! CHECK: %[[BASE_MAP:.*]] = omp.map.info {{.*}} map_clauses(implicit, tofrom) capture(ByRef) {{.*}} -> {{.*}} {name = ""}
! CHECK: %[[DESC_MAP:.*]] = omp.map.info {{.*}} map_clauses(always, implicit, to) capture(ByRef) members(%[[BASE_MAP]] : [0] : {{.*}}) -> {{.*}} {name = "obj"}
! CHECK: omp.target kernel_type(generic) map_entries(%[[DESC_MAP]] -> {{.*}}, %[[BASE_MAP]] -> {{.*}})
allocate(obj)
diff --git a/flang/test/Lower/OpenMP/derived-type-map.f90 b/flang/test/Lower/OpenMP/derived-type-map.f90
index a2f43afaccca2..8f45727534a2e 100644
--- a/flang/test/Lower/OpenMP/derived-type-map.f90
+++ b/flang/test/Lower/OpenMP/derived-type-map.f90
@@ -1,6 +1,6 @@
!RUN: %flang_fc1 -emit-hlfir -fopenmp %s -o - | FileCheck %s
-!CHECK: omp.declare_mapper @[[MAPPER1:_QQFmaptype_derived_implicit_allocatablescalar_and_array_omp_default_mapper]] : !fir.type<_QFmaptype_derived_implicit_allocatableTscalar_and_array{real:f32,array:!fir.array<10xi32>,int:i32}> {
+!CHECK-NOT: omp.declare_mapper
!CHECK: %[[ALLOCA:.*]] = fir.alloca !fir.type<_QFmaptype_derived_implicitTscalar_and_array{real:f32,array:!fir.array<10xi32>,int:i32}> {bindc_name = "scalar_arr", uniq_name = "_QFmaptype_derived_implicitEscalar_arr"}
!CHECK: %[[DECLARE:.*]]:2 = hlfir.declare %[[ALLOCA]] {uniq_name = "_QFmaptype_derived_implicitEscalar_arr"} : (!fir.ref<!fir.type<_QFmaptype_derived_implicitTscalar_and_array{real:f32,array:!fir.array<10xi32>,int:i32}>>) -> (!fir.ref<!fir.type<_QFmaptype_derived_implicitTscalar_and_array{real:f32,array:!fir.array<10xi32>,int:i32}>>, !fir.ref<!fir.type<_QFmaptype_derived_implicitTscalar_and_array{real:f32,array:!fir.array<10xi32>,int:i32}>>)
@@ -22,7 +22,7 @@ end subroutine mapType_derived_implicit
!CHECK: %[[ALLOCA:.*]] = fir.alloca !fir.box<!fir.heap<!fir.type<_QFmaptype_derived_implicit_allocatableTscalar_and_array{real:f32,array:!fir.array<10xi32>,int:i32}>>> {bindc_name = "scalar_arr", uniq_name = "_QFmaptype_derived_implicit_allocatableEscalar_arr"}
!CHECK: %[[DECLARE:.*]]:2 = hlfir.declare %[[ALLOCA]] {fortran_attrs = #fir.var_attrs<allocatable>, uniq_name = "_QFmaptype_derived_implicit_allocatableEscalar_arr"} : (!fir.ref<!fir.box<!fir.heap<!fir.type<_QFmaptype_derived_implicit_allocatableTscalar_and_array{real:f32,array:!fir.array<10xi32>,int:i32}>>>>) -> (!fir.ref<!fir.box<!fir.heap<!fir.type<_QFmaptype_derived_implicit_allocatableTscalar_and_array{real:f32,array:!fir.array<10xi32>,int:i32}>>>>, !fir.ref<!fir.box<!fir.heap<!fir.type<_QFmaptype_derived_implicit_allocatableTscalar_and_array{real:f32,array:!fir.array<10xi32>,int:i32}>>>>)
!CHECK: %[[BOX_ADDR:.*]] = fir.box_offset %[[DECLARE]]#1 base_addr : (!fir.ref<!fir.box<!fir.heap<!fir.type<_QFmaptype_derived_implicit_allocatableTscalar_and_array{real:f32,array:!fir.array<10xi32>,int:i32}>>>>) -> !fir.llvm_ptr<!fir.ref<!fir.type<_QFmaptype_derived_implicit_allocatableTscalar_and_array{real:f32,array:!fir.array<10xi32>,int:i32}>>>
-!CHECK: %[[BASE_MAP:.*]] = omp.map.info var_ptr(%[[DECLARE]]#1 : !fir.ref<!fir.box<!fir.heap<!fir.type<_QFmaptype_derived_implicit_allocatableTscalar_and_array{real:f32,array:!fir.array<10xi32>,int:i32}>>>>, !fir.box<!fir.heap<!fir.type<_QFmaptype_derived_implicit_allocatableTscalar_and_array{real:f32,array:!fir.array<10xi32>,int:i32}>>>) map_clauses(implicit, tofrom) capture(ByRef) var_ptr_ptr(%[[BOX_ADDR]] : !fir.llvm_ptr<!fir.ref<!fir.type<_QFmaptype_derived_implicit_allocatableTscalar_and_array{real:f32,array:!fir.array<10xi32>,int:i32}>>>, !fir.type<_QFmaptype_derived_implicit_allocatableTscalar_and_array{real:f32,array:!fir.array<10xi32>,int:i32}>) mapper(@[[MAPPER1]]) -> !fir.llvm_ptr<!fir.ref<!fir.type<_QFmaptype_derived_implicit_allocatableTscalar_and_array{real:f32,array:!fir.array<10xi32>,int:i32}>>> {name = ""}
+!CHECK: %[[BASE_MAP:.*]] = omp.map.info var_ptr(%[[DECLARE]]#1 : !fir.ref<!fir.box<!fir.heap<!fir.type<_QFmaptype_derived_implicit_allocatableTscalar_and_array{real:f32,array:!fir.array<10xi32>,int:i32}>>>>, !fir.box<!fir.heap<!fir.type<_QFmaptype_derived_implicit_allocatableTscalar_and_array{real:f32,array:!fir.array<10xi32>,int:i32}>>>) map_clauses(implicit, tofrom) capture(ByRef) var_ptr_ptr(%[[BOX_ADDR]] : !fir.llvm_ptr<!fir.ref<!fir.type<_QFmaptype_derived_implicit_allocatableTscalar_and_array{real:f32,array:!fir.array<10xi32>,int:i32}>>>, !fir.type<_QFmaptype_derived_implicit_allocatableTscalar_and_array{real:f32,array:!fir.array<10xi32>,int:i32}>) -> !fir.llvm_ptr<!fir.ref<!fir.type<_QFmaptype_derived_implicit_allocatableTscalar_and_array{real:f32,array:!fir.array<10xi32>,int:i32}>>> {name = ""}
!CHECK: %[[DESC_MAP:.*]] = omp.map.info var_ptr(%[[DECLARE]]#1 : !fir.ref<!fir.box<!fir.heap<!fir.type<_QFmaptype_derived_implicit_allocatableTscalar_and_array{real:f32,array:!fir.array<10xi32>,int:i32}>>>>, !fir.box<!fir.heap<!fir.type<_QFmaptype_derived_implicit_allocatableTscalar_and_array{real:f32,array:!fir.array<10xi32>,int:i32}>>>) map_clauses(always, implicit, to) capture(ByRef) members(%[[BASE_MAP]] : [0] : !fir.llvm_ptr<!fir.ref<!fir.type<_QFmaptype_derived_implicit_allocatableTscalar_and_array{real:f32,array:!fir.array<10xi32>,int:i32}>>>) -> !fir.ref<!fir.box<!fir.heap<!fir.type<_QFmaptype_derived_implicit_allocatableTscalar_and_array{real:f32,array:!fir.array<10xi32>,int:i32}>>>> {name = "scalar_arr"}
!CHECK: %[[ATTACH_MAP:.*]] = omp.map.info var_ptr(%[[DECLARE]]#1 : !fir.ref<!fir.box<!fir.heap<!fir.type<_QFmaptype_derived_implicit_allocatableTscalar_and_array{real:f32,array:!fir.array<10xi32>,int:i32}>>>>, !fir.box<!fir.heap<!fir.type<_QFmaptype_derived_implicit_allocatableTscalar_and_array{real:f32,array:!fir.array<10xi32>,int:i32}>>>) map_clauses(attach, ref_ptr, ref_ptee) capture(ByRef) var_ptr_ptr({{.*}} : !fir.llvm_ptr<!fir.ref<!fir.type<_QFmaptype_derived_implicit_allocatableTscalar_and_array{real:f32,array:!fir.array<10xi32>,int:i32}>>>, !fir.type<_QFmaptype_derived_implicit_allocatableTscalar_and_array{real:f32,array:!fir.array<10xi32>,int:i32}>) -> !fir.ref<!fir.box<!fir.heap<!fir.type<_QFmaptype_derived_implicit_allocatableTscalar_and_array{real:f32,array:!fir.array<10xi32>,int:i32}>>>> {name = "scalar_arr"}
!CHECK: omp.target kernel_type(generic) map_entries(%[[DESC_MAP]] -> %[[ARG0:.*]], %[[ATTACH_MAP]] -> %[[ARG1:.*]], %[[BASE_MAP]] -> %[[ARG2:.*]] : !fir.ref<!fir.box<!fir.heap<!fir.type<_QFmaptype_derived_implicit_allocatableTscalar_and_array{real:f32,array:!fir.array<10xi32>,int:i32}>>>>, !fir.ref<!fir.box<!fir.heap<!fir.type<_QFmaptype_derived_implicit_allocatableTscalar_and_array{real:f32,array:!fir.array<10xi32>,int:i32}>>>>, !fir.llvm_ptr<!fir.ref<!fir.type<_QFmaptype_derived_implicit_allocatableTscalar_and_array{real:f32,array:!fir.array<10xi32>,int:i32}>>>) {
diff --git a/flang/test/Lower/OpenMP/implicit-map-flat-allocatable-no-mapper.f90 b/flang/test/Lower/OpenMP/implicit-map-flat-allocatable-no-mapper.f90
new file mode 100644
index 0000000000000..009ad9669f4c6
--- /dev/null
+++ b/flang/test/Lower/OpenMP/implicit-map-flat-allocatable-no-mapper.f90
@@ -0,0 +1,23 @@
+! RUN: %flang_fc1 -emit-hlfir -fopenmp %s -o - | FileCheck %s
+
+! A flat derived type gets no implicit default mapper, even when the captured
+! variable is allocatable.
+
+program p
+ type t
+ integer :: x
+ real(8) :: v(4)
+ end type
+
+ type(t), allocatable :: al(:)
+ allocate(al(100))
+
+ !$omp target
+ al(1)%x = al(1)%x + 1
+ !$omp end target
+end program
+
+! CHECK-NOT: omp.declare_mapper
+
+! CHECK-LABEL: func.func @_QQmain
+! CHECK-NOT: mapper(
diff --git a/flang/test/Lower/OpenMP/implicit-map-pointer-no-default-mapper.f90 b/flang/test/Lower/OpenMP/implicit-map-pointer-no-default-mapper.f90
index 60a6db69acfa8..f98e92823a65a 100644
--- a/flang/test/Lower/OpenMP/implicit-map-pointer-no-default-mapper.f90
+++ b/flang/test/Lower/OpenMP/implicit-map-pointer-no-default-mapper.f90
@@ -1,7 +1,9 @@
! RUN: %flang_fc1 -emit-hlfir -fopenmp %s -o - | FileCheck %s
+
program p
type t
integer :: x
+ integer, allocatable :: y(:)
end type
type(t), pointer :: ptr
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