[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.

Author: agozillon

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;
   }
 

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:           }

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