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w6c+wwstage: source sub-8 value-struct ABI-size from tinfo.size at zero-init+DATAW (#254)

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wwstage conflated SLOT-size (round-to-8, for frame) with ABI-size (true)
for a nested value-struct. A nested value-struct field is sized via
fieldsize() (TY_STRUCT -> ti.slotsize = 8), poisoning structabisize and
registerstruct si.totsize to 8 for a struct whose true ABI size is 4.
Two emission sites then over-sized, both SILENT cs!=ww divergences:

  D1 (local, cgenstmt.ww cglet): zsz = structabisize = 8 hit the
     `zsz == 8` zero arm (#213) -> a stray `MOVQ $0, off(BP)` cstage
     never emits (ABI 4 is sub-8 -> left uninit per the shared no-rhs
     zero-init policy).
  D2 (global, cgen.ww emitletdataw): the struct zero arm wrote
     letemitsize/si.totsize = 8 DATAW bytes; cstage cg_let_emit_size
     returns u->size = 4.

Fix sources the zero-init extent from the type table's tinfo.size
(peeling TY_NAMED) at both sites — the same value cstage reads
(cgen.c:8397 / :978). fieldsize / registerstruct / frame slot-padding
stay UNTOUCHED: moving the fix into the size helpers would shift
nested-struct field offsets and re-diverge other byte-id. Pure
wwstage-align-down; cstage cmd/w6c/cgen.c unchanged.

Test 949_valstruct_subsize_run: D1 local + D2 global over ABI sizes
1/2/4 (the whole sub-8 / non-8-multiple class), each cstage-run +
cs==ww .s byte-id; plus a >8 (16B) local+global NEGATIVE control
proving the fix didn't disable legitimate multi-word zero-init.

Regen w6c + wwdump main.combined.ww (cgen is compiler-imported, #110).
This commit is contained in:
Hojun-Cho
2026-06-02 05:37:47 +09:00
parent e92708ecda
commit be23d7227a
6 changed files with 369 additions and 24 deletions
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6
Makefile
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@@ -405,6 +405,7 @@ TESTS = $(BIN)/test_smoke $(BIN)/test_lex $(BIN)/test_parse $(BIN)/test_check \
$(BIN)/test_dotbase_addr_slice_run \
$(BIN)/test_structlit_arrfield_run \
$(BIN)/test_arraytoslice_run \
$(BIN)/test_valstruct_subsize_run \
$(BIN)/test_continue_run \
$(BIN)/test_callret_unsigned_arith_run \
$(BIN)/test_sar_shr_run \
@@ -1611,6 +1612,11 @@ $(BIN)/test_arraytoslice_run: test/wcc/953_arraytoslice_run.c \
$(LIB)/libwwrt.a | $(BIN)
$(CC) $(CFLAGS) -o $@ $<
$(BIN)/test_valstruct_subsize_run: test/wcc/949_valstruct_subsize_run.c \
$(BIN)/ww $(BIN)/w6c $(BIN)/w6c_ww $(BIN)/w6a $(BIN)/w6l \
$(LIB)/libwwrt.a | $(BIN)
$(CC) $(CFLAGS) -o $@ $<
$(BIN)/test_continue_run: test/wcc/911_continue_run.c $(BIN)/ww \
$(BIN)/w6c $(BIN)/w6c_ww $(BIN)/w6a $(BIN)/w6l \
$(LIB)/libwwrt.a | $(BIN)