pub(crate) fn build_region_mapping(
source_regions: &[SourceRegionDescriptor],
target_regions: &[TargetRegionDescriptor],
transition_map: &[Vec<usize>],
) -> HashMap<RegionId, Vec<RegionId>>pub(crate) fn build_region_mapping(
source_regions: &[SourceRegionDescriptor],
target_regions: &[TargetRegionDescriptor],
transition_map: &[Vec<usize>],
) -> HashMap<RegionId, Vec<RegionId>>