Hojun-Cho
bacbf4b845
cgdot of a tagged-union struct field previously dropped the AX/DX/CX/R8 payload-register convention used by tagged-union returns: cstage's direct-struct branch stopped at CX (size > 16) and never loaded R8 (slice-payload variants, slot 32B); the via_ptr branch had no TY_TAGGED handler at all, falling through to fldloadop and yielding only the tag in AX. The N_DOT scrutinee fallback in N_MATCH similarly stored only AX into the spill slot. Wwstage cgdot had no TY_TAGGED branch in any of the direct, *struct, or top-level-global field-load paths, and cgmatch's non-ident scrutinee branch didn't recognise N_DOT — dispatch always computed want = 0 and the spill scratch was hardcoded 24B. The combined effect: any code reading `s.taggedfield` and consuming more than one quadword of the payload saw garbage in the upper halves. Cstage: extended the direct-struct TY_TAGGED branch with an R8 load for size > 24 (CX still loaded last so global LEAQ-into-CX rooting survives), added a parallel TY_TAGGED handler to the via_ptr (TY_PTR inner TY_STRUCT) field branch, and extended the N_DOT scrutinee spill fallback in N_MATCH to write DX/CX/R8 alongside AX. Wwstage: new cgloadtaggedfield helper emits the four-register load with CX-last ordering, and dotfieldtnode resolves a field's declared type node for a local-ident or *struct base. cgdot grew three TY_TAGGED branches (direct local, *struct deref staging in BX, top-level global through CX). cgmatch's non-ident-scrutinee branch grew an N_DOT type- extraction path mirroring the N_CALL / N_INDEX shapes and now sizes the @match_spill slot from slotsize(scrutt) so slice-payload variants don't overflow the historical 24B alloc. rhstaggedabicall accepts N_DOT so `let copy: ev = h.e;` and tagged-arg call sites pass through the tagged-source spill branch of cgwidentaggedstore. Out of scope for #28 and left as separate latents: wwstage's match-arm bind for a TY_STRUCT-typed variant copies only 8B (cstage falls back to bu->size; wwstage's bsz=8 default), and the variant-index lookup for an i64 literal in (i32 | i64) picks the wrong tag on the write side. Both surface in struct-payload tagged unions and merit their own tasks; the new test rows steer clear so #28's fix verifies end-to-end on scalar / str / slice payloads. Test 693_dot_tagged_source — three variant shapes (16B i64, 24B str, 32B slice) read from direct local, *struct param, top-level global, and let-init round-trip. The 32B-slice rows verify v.cap (R8 / +24) so dropping the upper-word load isn't masked by len-only checks; the top-level-global row routes the write through *p because the direct global-LHS tagged store is a separate wwstage gap (followup). Three negative controls (untagged i32 / str / slice fields) keep the new TY_TAGGED guard from shadowing the existing field-load paths. Wired into make test; 37 tests total. Bootstrap ww2 == ww3 == ww4 byte-identical.