Hojun-Cho fca979470f wcc/cgen: #52 error-first tagged-union success tag — successtag helper not hardcoded 0 (wwstage) ...

An error-first tagged union -- error variant at tag 0, success at tag 1+,
e.g. (myerr | u16) -- was silently miscompiled by wwstage: the try/propagate
codegen hardcoded success = tag 0, so the actual success value (tag 1)
failed the CMPQ $0 and fell to the error path -> exit(1) instead of the
value (44). cstage was correct (computes the success tag via
cg_tagged_success_tag = first non-error variant).

wwstage-only: a successtag/successvariant helper (mirroring cstage) replaces
the hardcoded tag-0 / first-param assumption at all four try sites --
cgtryprop (?), cgtryunw (!), and the two latent shift sites cgtrytupleshift
+ cgtrytaggedshift (which bite an error-first union with an aggregate
success payload). Success-first unions (the Hare idiom + what the selfhost
uses) keep successtag=0 -> CMPQ $0 unchanged -> byte-id-neutral on 990-997.
cstage untouched (w6c md5 unchanged).

byte-id 990-997 8/8. test/wcc/825 table-driven (errfirst must/prop +
tuple-success + success-first control). A separate nested-tagged-union
construction divergence is filed (#10/#125).

2026-06-08 22:15:19 +09:00

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