Regions, views, and provenance

A region is a lifetime domain whose allocations can be reclaimed together. AIF can bracket eligible work and route T1 sites to the active arena when every use is contained by that extent.

Lexical scope is only the starting point. Nonlexical analysis can end an extent after the last relevant use, but calls, aliases, loops, and returned values can prevent safe bracketing. Ambient region state is currently part of the runtime implementation, which is why concurrent region use requires special scrutiny.

Views preserve an owner relationship

A slice, struct field, enum payload, or reference-shaped container element can refer into storage owned by another value. The compiler records that provenance so an escaping view raises the required lifetime of its owner.

This rule is central to safe returned values. A function can return a view of a parameter without allocating, but the caller must not release the argument-position temporary before the returned view is consumed. When the compiler cannot prove the required relationship, it chooses the conservative lifetime.

Layout consequence

Under structure-of-arrays storage, an element may have no standalone address. A view is then a logical pair such as container identity plus index, not necessarily a raw interior pointer. Representation freedom depends on preserving this abstraction across sema, AIF, and lowering.

Tests must assert returned values in addition to allocation counts; balanced allocation bookkeeping cannot detect every dangling view.

Scope and region functions

aif_scope_new(parent, owner) creates the lexical tree used for least-common-ancestor escape joins. aif_scope_set_region and aif_scope_set_region_span mark an explicit region and its diagnostic location. aif_scope_note_node maps the source block back to the scope, while aif_scope_set_loop_depth records whether repeated execution changes placement cost.

aif_con_live_in(values, scope, fn) raises each reachable site's required lifetime to the named scope. aif_var_note_scope and aif_var_note_use record where bindings are declared and used. aif_scope_set_budget adds a region high-water assertion; aif_scope_budget, aif_scope_served, and the source accessors support reporting.

aif_place_arenas runs after tier solving. It rejects sites with blockers reported by aif_arena_blockers, groups eligible lifetimes, computes statement ranges, and chooses the scope/arena serving each site. aif_arena_range_first and aif_arena_range_last allow codegen to open and close a non-lexical arena around only the required statements.

Views are provenance edges

aif_vs_view_of(viewValues, collectionValues) records that a slice, string view, DataView, or element reference uses storage owned by another value. It does not create a new allocation site. When a view escapes, the solver raises the owner to the required lifetime.

Container stores are different: aif_con_store(key, values, owners) records both the field/element points-to edge and the set of owning containers. aif_con_retain_in records another holder. aif_elem_key is based on the full container type to avoid immediately merging List<Int> and List<Node>.

Interprocedural provenance

aif_note_call_result associates a call node with its abstract result. aif_fn_may_return_param computes whether a result may alias an input; aif_fn_may_return_view_of_param is the narrower view-provenance summary. aif_owns_call_result_at_node tells codegen whether the caller owns the result.

For region call bracketing, aif_call_edge records visible calls and aif_call_opaque records unknown ones. aif_bracket_count, aif_bracket_callee, aif_bracket_scope, and aif_bracket_served expose selected brackets; aif_fn_bracket_blockers explains why a function cannot safely run under a caller-owned arena.

Region tests must cover nested scopes, early return, break/continue, repeated loop execution, returned views, views stored in containers or fields, visible and opaque calls, recursive call graphs, budget overflow, and both lexical and non-lexical arena exit placement.