w6c+wwstage: read array field of a global struct (#249 BUG B)

Reading an array-typed field of a module-global struct value (`G.arr[i]`)
silently miscompiled: the N_INDEX fallback's cg_dotbase_addr (cstage) /
dotbaseaddr (wwstage) helper — the #135 sibling that computes &(s.field)
for a `[N]T` field — had no module-global-struct base arm. cstage emitted
`LEAQ (BP)` (localfind returns 0 for a global, so it read the stack frame
→ 0); wwstage's localfindnode returned nil and the fallback keyed on the
FIELD name, so it returned false and the caller's cgexpr(N_DOT) loaded the
field VALUE as a pointer → SEGFAULT. The .data was already correct
(emit_struct_lit_bytes #129 A.3); only the READ base address was wrong.

Both stages now emit `LEAQ name(SB) (+ ADDQ field_off)` for a global
value-struct base, mirroring the scalar global-field read (cgen.c:7532);
const globals resolve via def_isstructdef. Symmetric both stages (rule
10), byte-identical .s. Unblocks base64's `const std_encoding.encmap[i]`
reads (#22).

Test 949_structlit_arrfield_run: global `let`/`def` struct array-field
read, cstage run + cs==ww byte-id.

selfhost/cmd/w6c/main.combined.ww

@@ -20025,6 +20025,7 @@ fn dotbaseaddr(c: *cgen, base: *node, dstreg: str) bool = {
 	// 8 bytes as if it were a pointer-var — wrong shape (cstage
 	// sister fix in cg_dotbase_addr).
 	let lc: *local = localfindnode(c, inner.str);
+	let isglobal: bool = false;
 	if (lc == nil) {
 		let gt: *node = letvartnode(c, base.str);
 		if (gt != nil && gt.kind == nkind.N_TARRAY) {
@@ -20035,7 +20036,12 @@ fn dotbaseaddr(c: *cgen, base: *node, dstreg: str) bool = {
 			emitline("\n");
 			return true;
 		};
-		return false;
+		// #249 (sibling of #135): inner is a module-GLOBAL struct value
+		// (let/def), not a local — lc is nil but inner.type_ is a valid
+		// struct. Resolve the field below and emit a global base (LEAQ
+		// name(SB)). A non-struct inner (e.g. an SK_USE module qualifier,
+		// type ty_err) falls through the struct gate to `return false`.
+		isglobal = true;
 	};
 	let bu: *tinfo = inner.type_: *tinfo;
 	for (bu != nil && bu.kind == tykind.TY_NAMED) { bu = bu.under; };
@@ -20072,7 +20078,8 @@ fn dotbaseaddr(c: *cgen, base: *node, dstreg: str) bool = {
 	for (ft != nil && ft.kind == tykind.TY_NAMED) { ft = ft.under; };
 	if (ft == nil) { return false; };
 	if (ft.kind != tykind.TY_ARRAY) { return false; };
-	let innoff: i64 = lc.off: i64;
+	let innoff: i64 = 0;
+	if (lc != nil) { innoff = lc.off: i64; };
 	if (viaptr) {
 		emitline("\tMOVQ\t");
 		emitoff(innoff);
@@ -20086,6 +20093,21 @@ fn dotbaseaddr(c: *cgen, base: *node, dstreg: str) bool = {
 			emitline(dstreg);
 			emitline("\n");
 		};
+	} else if (isglobal) {
+		// #249: LEAQ name(SB) + field offset. Mirror cstage
+		// cg_dotbase_addr's global value-struct arm.
+		emitline("\tLEAQ\t");
+		emitsymname(c, inner.str);
+		emitline("(SB), ");
+		emitline(dstreg);
+		emitline("\n");
+		if (foff != 0) {
+			emitline("\tADDQ\t$");
+			emitint(foff);
+			emitline(", ");
+			emitline(dstreg);
+			emitline("\n");
+		};
 	} else {
 		emitline("\tLEAQ\t");
 		emitoff(innoff + foff);

selfhost/cmd/wcc/cgenexpr.ww

@@ -918,6 +918,7 @@ fn dotbaseaddr(c: *cgen, base: *node, dstreg: str) bool = {
 	// 8 bytes as if it were a pointer-var — wrong shape (cstage
 	// sister fix in cg_dotbase_addr).
 	let lc: *local = localfindnode(c, inner.str);
+	let isglobal: bool = false;
 	if (lc == nil) {
 		let gt: *node = letvartnode(c, base.str);
 		if (gt != nil && gt.kind == nkind.N_TARRAY) {
@@ -928,7 +929,12 @@ fn dotbaseaddr(c: *cgen, base: *node, dstreg: str) bool = {
 			emitline("\n");
 			return true;
 		};
-		return false;
+		// #249 (sibling of #135): inner is a module-GLOBAL struct value
+		// (let/def), not a local — lc is nil but inner.type_ is a valid
+		// struct. Resolve the field below and emit a global base (LEAQ
+		// name(SB)). A non-struct inner (e.g. an SK_USE module qualifier,
+		// type ty_err) falls through the struct gate to `return false`.
+		isglobal = true;
 	};
 	let bu: *tinfo = inner.type_: *tinfo;
 	for (bu != nil && bu.kind == tykind.TY_NAMED) { bu = bu.under; };
@@ -965,7 +971,8 @@ fn dotbaseaddr(c: *cgen, base: *node, dstreg: str) bool = {
 	for (ft != nil && ft.kind == tykind.TY_NAMED) { ft = ft.under; };
 	if (ft == nil) { return false; };
 	if (ft.kind != tykind.TY_ARRAY) { return false; };
-	let innoff: i64 = lc.off: i64;
+	let innoff: i64 = 0;
+	if (lc != nil) { innoff = lc.off: i64; };
 	if (viaptr) {
 		emitline("\tMOVQ\t");
 		emitoff(innoff);
@@ -979,6 +986,21 @@ fn dotbaseaddr(c: *cgen, base: *node, dstreg: str) bool = {
 			emitline(dstreg);
 			emitline("\n");
 		};
+	} else if (isglobal) {
+		// #249: LEAQ name(SB) + field offset. Mirror cstage
+		// cg_dotbase_addr's global value-struct arm.
+		emitline("\tLEAQ\t");
+		emitsymname(c, inner.str);
+		emitline("(SB), ");
+		emitline(dstreg);
+		emitline("\n");
+		if (foff != 0) {
+			emitline("\tADDQ\t$");
+			emitint(foff);
+			emitline(", ");
+			emitline(dstreg);
+			emitline("\n");
+		};
 	} else {
 		emitline("\tLEAQ\t");
 		emitoff(innoff + foff);

selfhost/cmd/wwdump/main.combined.ww

@@ -20025,6 +20025,7 @@ fn dotbaseaddr(c: *cgen, base: *node, dstreg: str) bool = {
 	// 8 bytes as if it were a pointer-var — wrong shape (cstage
 	// sister fix in cg_dotbase_addr).
 	let lc: *local = localfindnode(c, inner.str);
+	let isglobal: bool = false;
 	if (lc == nil) {
 		let gt: *node = letvartnode(c, base.str);
 		if (gt != nil && gt.kind == nkind.N_TARRAY) {
@@ -20035,7 +20036,12 @@ fn dotbaseaddr(c: *cgen, base: *node, dstreg: str) bool = {
 			emitline("\n");
 			return true;
 		};
-		return false;
+		// #249 (sibling of #135): inner is a module-GLOBAL struct value
+		// (let/def), not a local — lc is nil but inner.type_ is a valid
+		// struct. Resolve the field below and emit a global base (LEAQ
+		// name(SB)). A non-struct inner (e.g. an SK_USE module qualifier,
+		// type ty_err) falls through the struct gate to `return false`.
+		isglobal = true;
 	};
 	let bu: *tinfo = inner.type_: *tinfo;
 	for (bu != nil && bu.kind == tykind.TY_NAMED) { bu = bu.under; };
@@ -20072,7 +20078,8 @@ fn dotbaseaddr(c: *cgen, base: *node, dstreg: str) bool = {
 	for (ft != nil && ft.kind == tykind.TY_NAMED) { ft = ft.under; };
 	if (ft == nil) { return false; };
 	if (ft.kind != tykind.TY_ARRAY) { return false; };
-	let innoff: i64 = lc.off: i64;
+	let innoff: i64 = 0;
+	if (lc != nil) { innoff = lc.off: i64; };
 	if (viaptr) {
 		emitline("\tMOVQ\t");
 		emitoff(innoff);
@@ -20086,6 +20093,21 @@ fn dotbaseaddr(c: *cgen, base: *node, dstreg: str) bool = {
 			emitline(dstreg);
 			emitline("\n");
 		};
+	} else if (isglobal) {
+		// #249: LEAQ name(SB) + field offset. Mirror cstage
+		// cg_dotbase_addr's global value-struct arm.
+		emitline("\tLEAQ\t");
+		emitsymname(c, inner.str);
+		emitline("(SB), ");
+		emitline(dstreg);
+		emitline("\n");
+		if (foff != 0) {
+			emitline("\tADDQ\t$");
+			emitint(foff);
+			emitline(", ");
+			emitline(dstreg);
+			emitline("\n");
+		};
 	} else {
 		emitline("\tLEAQ\t");
 		emitoff(innoff + foff);