if check != nil {
				check.errorf(atPos(pos), InvalidUnion, "cannot handle more than %d union terms (implementation limitation)", maxTermCount)
			}
			unionSets[utyp] = &invalidTypeSet
			return unionSets[utyp]
		}
	}
	unionSets[utyp].terms = allTerms

	return unionSets[utyp]

			if check != nil {
				check.errorf(atPos(pos), InvalidUnion, "cannot handle more than %d union terms (implementation limitation)", maxTermCount)
			}
			unionSets[utyp] = &invalidTypeSet
			return unionSets[utyp]
		}
	}
	unionSets[utyp].terms = allTerms

	return unionSets[utyp]

		if y, _ := y.(*Union); y != nil {
			// TODO(rfindley): can this be reached during type checking? If so,
			// consider passing a type set map.
			unionSets := make(map[*Union]*_TypeSet)
			xset := computeUnionTypeSet(nil, unionSets, nopos, x)
			yset := computeUnionTypeSet(nil, unionSets, nopos, y)
			return xset.terms.equal(yset.terms)
		}

	case *Interface:

		if y, _ := y.(*Union); y != nil {
			// TODO(rfindley): can this be reached during type checking? If so,
			// consider passing a type set map.
			unionSets := make(map[*Union]*_TypeSet)
			xset := computeUnionTypeSet(nil, unionSets, nopos, x)
			yset := computeUnionTypeSet(nil, unionSets, nopos, y)
			return xset.terms.equal(yset.terms)
		}

	case *Interface:

        if (prev_resource_and_device != kInvalidResourceAndDevice) {
          // Merge class of current ID with class of previous ID since both
          // resources are accessed by `op`.
          resource_equivalence_classes.unionSets(prev_resource_and_device,
                                                 resource_and_device);
        } else {
          resource_equivalence_classes.insert(resource_and_device);
        }