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w6c+selfhost: cgen && and || short-circuit

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Both stages were eagerly evaluating RHS regardless of LHS (eager
ANDQ/ORQ on the two results). Now: eval LHS into AX, CMPQ $0 +
JE/JNE to a per-call-site label, eval RHS into AX, fall through.
AX holds the LHS sentinel on the skipped path — typechecker
already enforces bool operands.

Surfaced by lib/getopt's nil-argv guard segfault. Six new rows in
test/wcc/700_e2e.c, three of which segfault pre-fix. lib/getopt
test comment relaxed; nested-if kept as regression marker.
This commit is contained in:
Hojun-Cho
2026-05-13 19:21:43 +09:00
parent fbe0df4e68
commit 5bfdc7b20d
6 changed files with 141 additions and 18 deletions
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26
cmd/w6c/cgen.c
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@@ -1380,6 +1380,22 @@ cgexpr(Cg *c, Node *n, Local *locals)
}
break;
case N_BIN: {
/* Short-circuit `&&` / `||`. Operands are bool (0/1); the
* type checker enforces it. Eval LHS into AX, branch over
* RHS on the short-circuit polarity, otherwise eval RHS
* into AX. The surviving AX is the result. Must precede
* any eager-eval path below — `if (p != nil && p.x > 0)`
* would segfault on a nil deref otherwise. */
if (n->op == TK_AND || n->op == TK_OR) {
char *end = mklabel(c, n->op == TK_AND ? "andend" : "orend");
int jshrt = (n->op == TK_AND) ? A_JE : A_JNE;
cgexpr(c, n->lhs, locals);
ins2(c, A_CMPQ, aimm(0), areg(D_AX));
ins1(c, jshrt, abranch(end));
cgexpr(c, n->rhs, locals);
label(c, end);
break;
}
/* str == str / str != str — delegate to rt_streq, which
* does the byte-by-byte compare. */
if ((n->op == TK_EQ || n->op == TK_NEQ) &&
@@ -1550,14 +1566,8 @@ cgexpr(Cg *c, Node *n, Local *locals)
label(c, e);
break;
}
case TK_AND: case TK_OR: {
/* short-circuit not yet — eager evaluation. */
if (n->op == TK_AND)
ins2(c, A_ANDQ, areg(D_BX), areg(D_AX));
else
ins2(c, A_ORQ, areg(D_BX), areg(D_AX));
break;
}
/* TK_AND / TK_OR handled with short-circuit codegen at the
* top of N_BIN — they never reach this eager-eval switch. */
default: break;
}
break;