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cc1: Convert to variable unfoldable constants

When a constant expression cannot be folded then it is not constant
anymore because it needs run time operations to perform it. it also
derives to the fact that if a initializer contains one of these
expressions then the full initializer is not constant.

--- a/src/cmd/cc/cc1/fold.c

+++ b/src/cmd/cc/cc1/fold.c

@@ -454,8 +454,10 @@

 			type = UNSIGNED;

 	case PTR:

 	case FLOAT:

-		if ((p = foldconst(type, op, tp, ls, rs)) == NULL)

+		if ((p = foldconst(type, op, tp, ls, rs)) == NULL) {

+			np->flags &= ~NCONST;

 			return NULL;

+		}

 		freetree(np);

 		return p;

 	default:

--- a/src/cmd/cc/cc1/init.c

+++ b/src/cmd/cc/cc1/init.c

@@ -138,14 +138,14 @@

 static Node *

 mkcompound(Init *ip, Type *tp)

 {

-	Node **v, **p;

+	Node **v, **p, *np;

 	size_t n;

 	struct designator *dp, *next;

 	Symbol *sym;

+	int isconst = 1;

 	if (tp->op == UNION) {

-		Node *np = NULL;

-

+		np = NULL;

 		v = xmalloc(sizeof(*v));

 		for (dp = ip->head; dp; dp = next) {

 			freetree(np);

@@ -153,6 +153,8 @@

 			next = dp->next;

 			free(dp);

 		}

+		if ((np->flags & NCONST) == 0)

+			isconst = 0;

 		*v = np;

 	} else {

 		n = (tp->prop&TDEFINED) ? tp->n.elem : ip->max;

@@ -168,7 +170,10 @@

 			for (dp = ip->head; dp; dp = next) {

 				p = &v[dp->pos];

 				freetree(*p);

-				*p = dp->expr;

+				np = dp->expr;

+				*p = np;

+				if ((np->flags & NCONST) == 0)

+					isconst = 0;

 				next = dp->next;

 				free(dp);

 			}

@@ -180,7 +185,7 @@

 	sym->type = tp;

 	sym->flags |= SINITLST;

-	return constnode(sym);

+	return (isconst ? constnode : varnode)(sym);

 }

 static void

@@ -364,7 +369,7 @@

 	if (flags & SDEFINED) {

 		errorp("redeclaration of '%s'", sym->name);

 	} else if ((flags & (SGLOBAL|SLOCAL|SPRIVATE)) != 0) {

-		if (!(np->flags & NCONST)) {

+		if ((np->flags & NCONST) == 0) {

 			errorp("initializer element is not constant");

 			return;

 		}