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cmd/w6c/cgen+test: skip dead TRYPROP propret on same-shape ?

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Per CLAUDE.md rule 10, align cstage down to wwstage — when every
variant in a `?` propagation maps to itself, the remap loop emits
zero JMPs and the propret label is dead. Lazy-allocate it so the
label-counter ID is only consumed when at least one JMP fires.

Smoke test selfhost/test/trypromote.ww exercises same-shape
(i64|nomem)→(i64|nomem) propagation; cstage and wwstage now emit
byte-identical asm for the TRYPROP region.
This commit is contained in:
Hojun-Cho
2026-05-19 17:45:13 +09:00
parent 2b46abe7d1
commit 58e6d349a2
3 changed files with 64 additions and 2 deletions
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11
cmd/w6c/cgen.c
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@@ -5038,7 +5038,11 @@ cgexpr(Cg *c, Node *n, Local *locals)
ins2(c, A_CMPQ, aimm(s_tag), areg(D_AX));
ins1(c, A_JE, abranch(cont));
if (u && r && r->kind == TY_TAGGED && u->params) {
char *propret = mklabel(c, "tryprop_ret");
/* Same-shape unions remap every variant to itself, so
* the loop emits no JMPs. Skip propret entirely then —
* wwstage doesn't emit a dead label either (CLAUDE.md
* rule 10, task #18). */
char *propret = NULL;
int i = 0;
for (Tparam *p = u->params; p; p = p->next, i++) {
if (!cg_variant_is_error(u, i)) continue;
@@ -5049,10 +5053,13 @@ cgexpr(Cg *c, Node *n, Local *locals)
ins2(c, A_CMPQ, aimm(i), areg(D_AX));
ins1(c, A_JNE, abranch(skip));
ins2(c, A_MOVQ, aimm(j), areg(D_AX));
if (propret == NULL)
propret = mklabel(c, "tryprop_ret");
ins1(c, A_JMP, abranch(propret));
label(c, skip);
}
label(c, propret);
if (propret != NULL)
label(c, propret);
}
ins2(c, A_MOVQ, areg(D_BP), areg(D_SP));
ins1(c, A_POPQ, areg(D_BP));