[BUG] `LayoutDescription` leaks `LayoutConstraints`

[Jacobfaib]

Indirect leak of 798016 byte(s) in 674 object(s) allocated from:
      #0 0x7537cfce5357 in malloc (/lib64/libasan.so.8+0xfa357) (BuildId: 9e5b194837bcb1c45a484d4aff88710ee1e6b146)
      #1 0x7537b02de531 in void* Legion::Internal::legion_alloc_aligned<1184ul, 16ul, true>(unsigned long) /__w/legate.internal/legate.internal/build/_deps/legion-src/runtime/legion/legion_allocation.h:185
      #2 0x7537b00a3c1c in void* Legion::Internal::legion_alloc_aligned<Legion::Internal::LayoutConstraints, true>(unsigned long) /__w/legate.internal/legate.internal/build/_deps/legion-src/runtime/legion/legion_allocation.h:198
      #3 0x7537b00a3c1c in Legion::Internal::LegionHeapify<Legion::Internal::LayoutConstraints>::operator new(unsigned long) /__w/legate.internal/legate.internal/build/_deps/legion-src/runtime/legion/legion_allocation.h:318
      #4 0x7537b00a3c1c in Legion::Internal::Runtime::register_layout(Legion::FieldSpace, Legion::LayoutConstraintSet const&, bool) /__w/legate.internal/legate.internal/build/_deps/legion-src/runtime/legion/runtime.cc:33987
      #5 0x7537b00a46c2 in Legion::Internal::MemoryManager::create_unbound_instance(Legion::LogicalRegion, Legion::LayoutConstraintSet&, Legion::Internal::ApEvent, unsigned int, Realm::Processor, int) /__w/legate.internal/legate.internal/build/_deps/legion-src/runtime/legion/runtime.cc:12726
      #6 0x7537af510a96 in Legion::Internal::SingleTask::prepare_output_instance(unsigned int, Legion::Internal::InstanceSet&, Legion::RegionRequirement const&, Realm::Memory, Legion::LayoutConstraintSet const&) /__w/legate.internal/legate.internal/build/_deps/legion-src/runtime/legion/legion_tasks.cc:3397
      #7 0x7537af5383a7 in Legion::Internal::SingleTask::finalize_map_task_output(Legion::Mapping::Mapper::MapTaskInput&, Legion::Mapping::Mapper::MapTaskOutput&, Legion::Internal::MustEpochOp*) /__w/legate.internal/legate.internal/build/_deps/legion-src/runtime/legion/legion_tasks.cc:3231
      #8 0x7537af53a14e in Legion::Internal::IndividualTask::finalize_map_task_output(Legion::Mapping::Mapper::MapTaskInput&, Legion::Mapping::Mapper::MapTaskOutput&, Legion::Internal::MustEpochOp*) /__w/legate.internal/legate.internal/build/_deps/legion-src/runtime/legion/legion_tasks.cc:6920
      #9 0x7537af47a49d in Legion::Internal::SingleTask::invoke_mapper(Legion::Internal::MustEpochOp*) /__w/legate.internal/legate.internal/build/_deps/legion-src/runtime/legion/legion_tasks.cc:3745
      #10 0x7537af4cefaa in Legion::Internal::SingleTask::map_all_regions(Legion::Internal::MustEpochOp*, Legion::Internal::TaskOp::DeferMappingArgs const*) /__w/legate.internal/legate.internal/build/_deps/legion-src/runtime/legion/legion_tasks.cc:4249
      #11 0x7537af4d632c in Legion::Internal::IndividualTask::perform_mapping(Legion::Internal::MustEpochOp*, Legion::Internal::TaskOp::DeferMappingArgs const*) /__w/legate.internal/legate.internal/build/_deps/legion-src/runtime/legion/legion_tasks.cc:6895
      #12 0x7537af3b48c0 in Legion::Internal::SingleTask::trigger_mapping() /__w/legate.internal/legate.internal/build/_deps/legion-src/runtime/legion/legion_tasks.cc:2488
      #13 0x7537b020c1c1 in Legion::Internal::Runtime::legion_runtime_task(void const*, unsigned long, void const*, unsigned long, Realm::Processor) /__w/legate.internal/legate.internal/build/_deps/legion-src/runtime/legion/runtime.cc:36366

The chain of calls appears to be:

1. MemoryManager::create_unbound_instance().
2. Calls runtime->register_layout() to create the constraints.
3. Which is passed to fspace_node->create_layout_description().
4. Which passes the layout constraints to LayoutDescription().
5. Which eventually (somehow) fails to free the LayoutConstraints.

[lightsighter]

Right, because your mapper is leaking the PhysicalInstance associated with this layout constraint. Assigning back to @Jacobfaib to provide a stand-alone reproducer that shows that all the PhysicalInstance objects in the mapper are deleted and this still leaks.