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MIR lowering for object field access and expanded parameters

Summary

object-typed values are lowered as flattened per-field locals (__li_o_<root>_<field>…) for field access, assignment, var, expanded call arguments, same-type var dst: T = srcIdent slot copies, whole-object assigns, element-wise copy of fixed array[N, int|float] fields, and LLVM struct returns that pack scalars and fixed arrays as [N x T] members (ReturnObject, callee unpack, var w: T = foo()).

Agent continuation

  1. Read compiler/mir/include/li/mir.hpp (ReturnObject, MirFn::returns_object / return_object_layout, MirInsn::object_layout), compiler/mir/lower.cpp, compiler/codegen/emit.cpp.
  2. Run cmake --build build then ./li-tests/run_all.sh encapsulation and ./li-tests/run_all.sh math_linalg with LIC pointing at the built lic.
  3. Next: array fields with i64 / other scalar elems in struct returns; extern proc returning object; typedict parity.
  4. Blocked: array fields with element types other than int / float (e.g. i64) on object return/param paths; nested extern object ABI.

Changed

  • compiler/mir/include/li/mir.hpp — MirParam::fixed_array_elems; comments for ReturnObject / object_layout.
  • compiler/mir/lower.cpp — collect_object_return_layout_r / append_mir_params_for_object_type include fixed array[N, int|float]; implicit ReturnObject zero uses per-index ArrayStore* for those fields; seed_*_params skip fixed-array param roots; prior object work unchanged (ReturnObject, CallProc temps, var/Assign copies, emit_copy_array_slots_r, g_arr_ctx, Index / Assign FieldAccess bases, deferred g_arr_ctx clear).
  • compiler/codegen/emit.cpp — llvm_type_for_mir_param, LLVM struct fields [N x T], ReturnObject aggregate load, CallProc aggregate store to ArrayAlloc slots, mir_arg_value loads for array idents, prologue stores for expanded array params.
  • li-tests/objects/object_array_return_call.li — callee returns object whose only field is array[2, int].
  • li-tests/objects/object_mixed_scalar_array_return.li — struct return with int, array[2, int], int fields (ordering vs layout).
  • li-tests/objects/object_mixed_param_pass.li — expanded Mixed object parameter (scalar + array[2,int]) passed to callee.
  • li-tests/manifest.toml — register object_mixed_param_pass.li.

Not changed

  • General scalar/control-flow codegen paths in emit.cpp beyond struct-return / aggregate-array plumbing.
  • typedict runtime layout (still not flattened in MIR).
  • Parser, borrow checker, and verifier contracts for objects.
  • Dominance: object_locals is a flat map from the whole procedure AST; assigning to a name that is not object-typed or not declared on all paths may still be accepted by the typechecker separately from MIR slot layout.
  • extern proc returning a Li object type (no struct lowering contract).
  • return_object_layout / LLVM struct fields for array elements other than int / float (e.g. i64) remain unsupported.

Breaking

N/A — fixes incorrect codegen for programs that already type-checked.

Security

N/A.

Performance

N/A — same stack locals as before for scalar object fields; more MIR parameters for object-by-value calls (ABI expansion).

Downstream

Callers of procs that take object parameters must pass the same Li source (compiler expands arguments); no C ABI change for non-object programs.