[flang][hlfir] Support box in user defined assignments (#77578)

When dealing with overlaps in user defined assignments, some entities
with descriptors (fir.box) may be saved without descriptors. The current
code was replacing the original box entity with the "raw" copy with a
simple cast instead of creating a box for the copy. This patch ensures a
fir.embox is emitted instead.

flang/lib/Optimizer/HLFIR/Transforms/LowerHLFIROrderedAssignments.cpp

@@ -421,6 +421,14 @@ convertToMoldType(mlir::Location loc, fir::FirOpBuilder &builder,
   }
   // Variable to Variable mismatch (e.g., fir.heap<T> vs fir.ref<T>), or value
   // to Value mismatch (e.g. i1 vs fir.logical<4>).
+  if (mlir::isa<fir::BaseBoxType>(mold.getType()) &&
+      !mlir::isa<fir::BaseBoxType>(input.getType())) {
+    // An entity may have have been saved without descriptor while the original
+    // value had a descriptor (e.g., it was not contiguous).
+    auto emboxed = hlfir::convertToBox(loc, builder, input, mold.getType());
+    assert(!emboxed.second && "temp should already be in memory");
+    input = hlfir::Entity{fir::getBase(emboxed.first)};
+  }
   return hlfir::Entity{builder.createConvert(loc, mold.getType(), input)};
 }
 

flang/test/HLFIR/order_assignments/user-defined-assignment.fir

@@ -180,3 +180,26 @@ func.func @test_scalar_forall_overlap(%i: !fir.ref<!fir.array<10xi32>>) {
 // CHECK:    fir.call @logical_value_to_numeric(%[[VAL_32]], %[[VAL_33]]) : (!fir.ref<i32>, !fir.logical<4>) -> ()
 // CHECK:  }
 // CHECK:  fir.freemem %[[VAL_15]] : !fir.heap<!fir.array<?xi1>>
+
+func.func @test_saved_scalar_box(%arg0: !fir.box<!fir.type<sometype>>, %arg1: !fir.class<!fir.type<sometype>>) {
+  hlfir.region_assign {
+    hlfir.yield %arg0 : !fir.box<!fir.type<sometype>>
+  } to {
+    hlfir.yield %arg1 : !fir.class<!fir.type<sometype>>
+  } user_defined_assign  (%arg2: !fir.box<!fir.type<sometype>>) to (%arg3: !fir.class<!fir.type<sometype>>) {
+    fir.call @user_assign_box(%arg3, %arg2) : (!fir.class<!fir.type<sometype>>, !fir.box<!fir.type<sometype>>) -> ()
+  }
+  return
+}
+func.func private @user_assign_box(!fir.class<!fir.type<sometype>>, !fir.box<!fir.type<sometype>>) -> ()
+
+// CHECK-LABEL:   func.func @test_saved_scalar_box(
+// CHECK-SAME:                    %[[VAL_0:.*]]: !fir.box<!fir.type<sometype>>,
+// CHECK-SAME:                    %[[VAL_1:.*]]: !fir.class<!fir.type<sometype>>) {
+// CHECK:           %[[VAL_2:.*]] = hlfir.as_expr %[[VAL_0]] : (!fir.box<!fir.type<sometype>>) -> !hlfir.expr<!fir.type<sometype>>
+// CHECK:           %[[VAL_3:.*]]:3 = hlfir.associate %[[VAL_2]]
+// CHECK:           %[[VAL_4:.*]] = fir.embox %[[VAL_3]]#1 : (!fir.ref<!fir.type<sometype>>) -> !fir.box<!fir.type<sometype>>
+// CHECK:           fir.call @user_assign_box(%[[VAL_1]], %[[VAL_4]]) : (!fir.class<!fir.type<sometype>>, !fir.box<!fir.type<sometype>>) -> ()
+// CHECK:           hlfir.end_associate %[[VAL_3]]#1, %[[VAL_3]]#2 : !fir.ref<!fir.type<sometype>>, i1
+// CHECK:           return
+// CHECK:         }