Summary

Add cranelift-entity dependency to trunk-ir and implement the core arena-based IR infrastructure.

Scope

• Add cranelift-entity to crates/trunk-ir/Cargo.toml
• Define typed indices: OpRef, ValueRef, BlockRef, RegionRef (via entity_impl!)
• Implement IrContext with PrimaryMap-backed storage for all node types
• Implement CRUD operations: create_op, remove_op, create_block, create_region, etc.
• Implement use-chain tracking in ValueData (SmallVec<[Use; 4]>)
• Implement replace_all_uses(old, new) (RAUW) with O(uses) complexity
• Auto-maintain use-chains on op create/remove

Key Types

pub struct OpRef(u32);
entity_impl!(OpRef, "op");

pub struct Use { pub user: OpRef, pub operand_index: u32 }

pub struct ValueData {
    pub def: ValueDef,
    pub ty: TypeRef,
    pub uses: SmallVec<[Use; 4]>,
}

pub struct OperationData {
    pub dialect: Symbol,
    pub name: Symbol,
    pub operands: EntityList<ValueRef>,
    pub results: EntityList<ValueRef>,
    pub attributes: BTreeMap<Symbol, Attribute>,
    pub regions: SmallVec<[RegionRef; 1]>,
    pub successors: SmallVec<[BlockRef; 2]>,
    pub location: Location,
    pub parent_block: Option<BlockRef>,
}

Key Files

• crates/trunk-ir/Cargo.toml
• crates/trunk-ir/src/arena/ (new module)

Acceptance Criteria

• cranelift-entity added as dependency
• All typed refs defined with entity_impl!
• IrContext supports create/read/remove for ops, values, blocks, regions
• Use-chain automatically maintained on create/remove
• replace_all_uses works correctly
• Unit tests for CRUD and RAUW