[flang-commits] [flang] 7a7a207 - [Flang][OpenMP] Remove forced close mapping for descriptor in USM (#215350)

[via flang-commits]

Author: agozillon
Date: 2026-08-18T23:51:36+02:00
New Revision: 7a7a2070f21962c030ff5e4e1c03e03a05e7094c

URL: https://github.com/llvm/llvm-project/commit/7a7a2070f21962c030ff5e4e1c03e03a05e7094c
DIFF: https://github.com/llvm/llvm-project/commit/7a7a2070f21962c030ff5e4e1c03e03a05e7094c.diff

LOG: [Flang][OpenMP] Remove forced close mapping for descriptor in USM (#215350)

This was added originally to solve an issue with pointer checking on USM
devices (usm_map_close.f90 in the fortran offload tests) but no longer
appears to be required.

None the less, this isn't a fix we can keep around, we cannot force
close mapping on things, we should only carry it over if a user
specifies it (done so above). As if we force it onto the descriptor,
then on USM architectures in USM mode we're actually inflicting the user
with unwanted and unrequested host to device transfers. As we're saying
we want the descriptor to be placed in memory as close to the device as
possible (so device memory). We shouldn't make the assumption this is
what a user wishes, especially when they can now refine there mappings
to specify what they want done with the descriptor.

So, removing this as a performance and correctness optimization now that
it no longer appears to be required for the usm_map_close.f90 test on at
least a fully USM enabled system like gfx942.

There's a few other cases like this in MapInfoFinalization I think that
may need a similar revision.

Added: 
    flang/test/Lower/OpenMP/usm-descriptor-close-map.f90

Modified: 
    flang/lib/Optimizer/OpenMP/MapInfoFinalization.cpp

Removed: 
    


################################################################################
diff  --git a/flang/lib/Optimizer/OpenMP/MapInfoFinalization.cpp b/flang/lib/Optimizer/OpenMP/MapInfoFinalization.cpp
index 5d1305b32c0eb..8fc3d85ce7a7e 100644
--- a/flang/lib/Optimizer/OpenMP/MapInfoFinalization.cpp
+++ b/flang/lib/Optimizer/OpenMP/MapInfoFinalization.cpp
@@ -855,11 +855,6 @@ class MapInfoFinalizationPass
                  ? MapFlags::close
                  : MapFlags::always;
 
-    // For unified_shared_memory, we additionally add `CLOSE` on the descriptor
-    // to ensure device-local placement where required by tests relying on USM +
-    // close semantics.
-    if (moduleRequiresUSM(target->getParentOfType<mlir::ModuleOp>()))
-      flags |= MapFlags::close;
     return flags;
   }
 

diff  --git a/flang/test/Lower/OpenMP/usm-descriptor-close-map.f90 b/flang/test/Lower/OpenMP/usm-descriptor-close-map.f90
new file mode 100644
index 0000000000000..a9eef8f29ce99
--- /dev/null
+++ b/flang/test/Lower/OpenMP/usm-descriptor-close-map.f90
@@ -0,0 +1,35 @@
+! RUN: %flang_fc1 -emit-hlfir -fopenmp -fopenmp-version=50 %s -o - | FileCheck %s
+
+! Verify that we appropriately apply the close map type to the descriptor when it is
+! explicitly specified and that we do not strip it needlessly in USM or otherwise add
+! it to the descriptor implicitly like we used to.
+
+module usm_descriptor_close_map
+  !$omp requires unified_shared_memory
+contains
+
+! CHECK-LABEL: func.func @_QMusm_descriptor_close_mapPusm_only
+! CHECK: %[[DECL:.*]]:2 = hlfir.declare %{{.*}} {fortran_attrs = #fir.var_attrs<pointer>, {{.*}}Epoint"}
+! CHECK: %[[BOX_OFF:.*]] = fir.box_offset %[[DECL]]#1 base_addr : (!fir.ref<!fir.box<!fir.ptr<i32>>>) -> !fir.llvm_ptr<!fir.ref<i32>>
+! CHECK: %[[MEMBER:.*]] = omp.map.info var_ptr(%[[DECL]]#1 : !fir.ref<!fir.box<!fir.ptr<i32>>>, !fir.box<!fir.ptr<i32>>) map_clauses(tofrom) capture(ByRef) var_ptr_ptr(%[[BOX_OFF]] : !fir.llvm_ptr<!fir.ref<i32>>, i32) -> !fir.llvm_ptr<!fir.ref<i32>> {name = ""}
+! CHECK: %[[DESC_MAP:.*]] = omp.map.info var_ptr(%[[DECL]]#1 : !fir.ref<!fir.box<!fir.ptr<i32>>>, !fir.box<!fir.ptr<i32>>) map_clauses(always, to) capture(ByRef) members(%[[MEMBER]] : [0] : !fir.llvm_ptr<!fir.ref<i32>>) -> !fir.ref<!fir.box<!fir.ptr<i32>>> {name = "point"}
+  subroutine usm_only(point)
+    integer, pointer :: point
+    !$omp target map(tofrom: point)
+    point = 1
+    !$omp end target
+  end subroutine
+
+! CHECK-LABEL: func.func @_QMusm_descriptor_close_mapPusm_explicit_close
+! CHECK: %[[DECL:.*]]:2 = hlfir.declare %{{.*}} {fortran_attrs = #fir.var_attrs<pointer>, {{.*}}Epoint"}
+! CHECK: %[[BOX_OFF:.*]] = fir.box_offset %[[DECL]]#1 base_addr : (!fir.ref<!fir.box<!fir.ptr<i32>>>) -> !fir.llvm_ptr<!fir.ref<i32>>
+! CHECK: %[[MEMBER:.*]] = omp.map.info var_ptr(%[[DECL]]#1 : !fir.ref<!fir.box<!fir.ptr<i32>>>, !fir.box<!fir.ptr<i32>>) map_clauses(close, tofrom) capture(ByRef) var_ptr_ptr(%[[BOX_OFF]] : !fir.llvm_ptr<!fir.ref<i32>>, i32) -> !fir.llvm_ptr<!fir.ref<i32>> {name = ""}
+! CHECK: %[[DESC_MAP:.*]] = omp.map.info var_ptr(%[[DECL]]#1 : !fir.ref<!fir.box<!fir.ptr<i32>>>, !fir.box<!fir.ptr<i32>>) map_clauses(close, to) capture(ByRef) members(%[[MEMBER]] : [0] : !fir.llvm_ptr<!fir.ref<i32>>) -> !fir.ref<!fir.box<!fir.ptr<i32>>> {name = "point"}
+  subroutine usm_explicit_close(point)
+    integer, pointer :: point
+    !$omp target map(close, tofrom: point)
+    point = 1
+    !$omp end target
+  end subroutine
+
+end module