[flang-commits] [flang] [llvm] [Flang][OpenMP][MLIR] Check for presence of Box type before emitting store in MapInfoFinalization pass (PR #135477)

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https://github.com/agozillon created https://github.com/llvm/llvm-project/pull/135477

Currently we don't check for the presence of descriptor/BoxTypes before emitting stores which lower to memcpys, the issue with this is that users can have optional arguments, where they don't provide an input, making the argument effectively null. This can still be mapped and this causes issues at the moment as we'll emit a memcpy for function arguments to store to a local variable for certain edge cases, when we perform this memcpy on a null input, we cause a segfault at runtime.

The fix to this is to simply create a branch around the store that checks if the data we're copying from is actually present. If it is, we proceed with the store, if it isn't we skip it.

>From aa6d5d6e14ba92375a606cfa38ebea0af9ca353d Mon Sep 17 00:00:00 2001
From: agozillon <Andrew.Gozillon at amd.com>
Date: Sat, 12 Apr 2025 00:30:30 -0500
Subject: [PATCH] [Flang][OpenMP][MLIR] Check for presence of Box type before
 emitting store in MapInfoFinalization pass

Currently we don't check for the presence of descriptor/BoxTypes before emitting stores which lower
to memcpys, the issue with this is that users can have optional arguments, where they don't provide
an input, making the argument effectively null. This can still be mapped and this causes issues
at the moment as we'll emit a memcpy for function arguments to store to a local variable for certain
edge cases, when we perform this memcpy on a null input, we cause a segfault at runtime.

The fix to this is to simply create a branch around the store that checks if the data we're copying
from is actually present. If it is, we procede with the store, if it isn't we skip it.
---
 .../Optimizer/OpenMP/MapInfoFinalization.cpp  | 10 +++++-
 .../Lower/OpenMP/optional-argument-map.f90    | 27 ++++++++++++++
 .../fortran/optional-mapped-arguments.f90     | 36 +++++++++++++++++++
 3 files changed, 72 insertions(+), 1 deletion(-)
 create mode 100644 flang/test/Lower/OpenMP/optional-argument-map.f90
 create mode 100644 offload/test/offloading/fortran/optional-mapped-arguments.f90

diff --git a/flang/lib/Optimizer/OpenMP/MapInfoFinalization.cpp b/flang/lib/Optimizer/OpenMP/MapInfoFinalization.cpp
index 61f8713028a7f..3fcb4b04a7b76 100644
--- a/flang/lib/Optimizer/OpenMP/MapInfoFinalization.cpp
+++ b/flang/lib/Optimizer/OpenMP/MapInfoFinalization.cpp
@@ -153,7 +153,15 @@ class MapInfoFinalizationPass
     builder.setInsertionPointToStart(allocaBlock);
     auto alloca = builder.create<fir::AllocaOp>(loc, descriptor.getType());
     builder.restoreInsertionPoint(insPt);
-    builder.create<fir::StoreOp>(loc, descriptor, alloca);
+    // We should only emit a store if the passed in data is present, it is
+    // possible a user passes in no argument to an optional parameter, in which
+    // case we cannot store or we'll segfault on the emitted memcpy.
+    auto isPresent =
+        builder.create<fir::IsPresentOp>(loc, builder.getI1Type(), descriptor);
+    builder.genIfOp(loc, {}, isPresent, false)
+        .genThen(
+            [&]() { builder.create<fir::StoreOp>(loc, descriptor, alloca); })
+        .end();
     return slot = alloca;
   }
 
diff --git a/flang/test/Lower/OpenMP/optional-argument-map.f90 b/flang/test/Lower/OpenMP/optional-argument-map.f90
new file mode 100644
index 0000000000000..863742ce67927
--- /dev/null
+++ b/flang/test/Lower/OpenMP/optional-argument-map.f90
@@ -0,0 +1,27 @@
+!RUN: %flang_fc1 -emit-hlfir -fopenmp %s -o - | FileCheck %s
+
+module foo
+    implicit none
+    contains
+    subroutine test(I,A)
+      implicit none
+      real(4), optional, intent(inout) :: A(:)
+      integer(kind=4), intent(in) :: I
+
+     !$omp target data map(to: A) if (I>0)
+     !$omp end target data
+
+    end subroutine test
+end module foo
+
+! CHECK-LABEL:   func.func @_QMfooPtest(
+! CHECK-SAME:                           %[[VAL_0:.*]]: !fir.ref<i32> {fir.bindc_name = "i"},
+! CHECK-SAME:                           %[[VAL_1:.*]]: !fir.box<!fir.array<?xf32>> {fir.bindc_name = "a", fir.optional}) {
+! CHECK:           %[[VAL_2:.*]] = fir.alloca !fir.box<!fir.array<?xf32>>
+! CHECK:           %[[VAL_3:.*]]:2 = hlfir.declare %[[VAL_1]] dummy_scope %{{.*}} {fortran_attrs = #fir.var_attrs<intent_inout, optional>, uniq_name = "_QMfooFtestEa"} : (!fir.box<!fir.array<?xf32>>, !fir.dscope) -> (!fir.box<!fir.array<?xf32>>, !fir.box<!fir.array<?xf32>>)
+! CHECK:           %{{.*}} = fir.is_present %{{.*}}#1 : (!fir.box<!fir.array<?xf32>>) -> i1
+! CHECK:           %{{.*}}:5 = fir.if %{{.*}}
+! CHECK:           %[[VAL_4:.*]] = fir.is_present %[[VAL_3]]#1 : (!fir.box<!fir.array<?xf32>>) -> i1
+! CHECK:           fir.if %[[VAL_4]] {
+! CHECK:             fir.store %[[VAL_3]]#1 to %[[VAL_2]] : !fir.ref<!fir.box<!fir.array<?xf32>>>
+! CHECK:           }
diff --git a/offload/test/offloading/fortran/optional-mapped-arguments.f90 b/offload/test/offloading/fortran/optional-mapped-arguments.f90
new file mode 100644
index 0000000000000..e0cdddb8e1bf7
--- /dev/null
+++ b/offload/test/offloading/fortran/optional-mapped-arguments.f90
@@ -0,0 +1,36 @@
+! OpenMP offloading test that checks we do not cause a segfault when mapping
+! optional function arguments (present or otherwise). No results requiring
+! checking other than that the program compiles and runs to completion with no
+! error.
+! REQUIRES: flang, amdgpu
+
+! RUN: %libomptarget-compile-fortran-run-and-check-generic
+module foo
+    implicit none
+    contains
+    subroutine test(I,A)
+        implicit none
+        real(4), optional, intent(inout) :: A(:)
+        integer(kind=4), intent(in) :: I
+
+        !$omp target data map(to: A) if (I>0)
+        !$omp end target data
+
+        !$omp target enter data map(to:A) if (I>0)
+
+        !$omp target exit data map(from:A) if (I>0)
+    end subroutine test
+end module foo
+
+program main
+    use foo
+    implicit none
+    real :: array(10)
+    call test(0)
+    call test(1)
+    call test(0, array)
+    call test(1, array)
+    print *, "PASSED"
+end program main
+
+! CHECK: PASSED