declared and not used error, but disabled.

fix some bugs involving _.

R=ken
OCL=34621
CL=34621

src/cmd/gc/gen.c

@@ -26,6 +26,7 @@ allocparams(void)
 	Node *n;
 	uint32 w;
 	Sym *s;
+	int lno;
 
 	if(stksize < 0)
 		fatal("allocparams not during code generation");
@@ -35,6 +36,7 @@ allocparams(void)
 	 * slots for all automatics.
 	 * allocated starting at -w down.
 	 */
+	lno = lineno;
 	for(l=curfn->dcl; l; l=l->next) {
 		n = l->n;
 		if(n->op == ONAME && n->class == PHEAP-1) {
@@ -46,19 +48,21 @@ allocparams(void)
 		}
 		if(n->op != ONAME || n->class != PAUTO)
 			continue;
-		typecheck(&n, Erv);	// only needed for unused variables
+		lineno = n->lineno;
+		typecheck(&n, Erv | Easgn);	// only needed for unused variables
 		if(n->type == T)
 			continue;
+	//	if(!n->used && n->sym->name[0] != '&')
+	//		yyerror("%S declared and not used", n->sym);
 		dowidth(n->type);
 		w = n->type->width;
-		if(n->class & PHEAP)
-			w = widthptr;
 		if(w >= 100000000)
 			fatal("bad width");
 		stksize += w;
 		stksize = rnd(stksize, w);
 		n->xoffset = -stksize;
 	}
+	lineno = lno;
 }
 
 void

src/cmd/gc/go.h

@@ -201,6 +201,7 @@ struct	Node
 	uchar	local;
 	uchar	initorder;
 	uchar	dodata;		// compile literal assignment as data statement
+	uchar	used;
 
 	// most nodes
 	Node*	left;

src/cmd/gc/go.y

@@ -456,6 +456,7 @@ case:
 		if(typesw != N && typesw->right != N && (n=typesw->right->left) != N) {
 			// type switch - declare variable
 			n = newname(n->sym);
+			n->used = 1;	// TODO(rsc): better job here
 			declare(n, dclcontext);
 			$$->nname = n;
 		}
@@ -488,6 +489,7 @@ case:
 		if(typesw != N && typesw->right != N && (n=typesw->right->left) != N) {
 			// type switch - declare variable
 			n = newname(n->sym);
+			n->used = 1;	// TODO(rsc): better job here
 			declare(n, dclcontext);
 			$$->nname = n;
 		}

src/cmd/gc/typecheck.c

@@ -112,9 +112,13 @@ reswitch:
 			ok |= Ecall;
 			goto ret;
 		}
-		if(isblank(n) && !(top & Easgn)) {
-			yyerror("cannot use _ as value");
-			goto error;
+		if(!(top & Easgn)) {
+			// not a write to the variable
+			if(isblank(n)) {
+				yyerror("cannot use _ as value");
+				goto error;
+			}
+			n->used = 1;
 		}
 		ok |= Erv;
 		goto ret;

src/cmd/gc/walk.c

@@ -1771,6 +1771,9 @@ convas(Node *n, NodeList **init)
 	if(lt == T || rt == T)
 		goto out;
 
+	if(isblank(n->left))
+		goto out;
+
 	if(n->left->op == OINDEXMAP) {
 		n = mkcall1(mapfn("mapassign1", n->left->left->type), T, init,
 			n->left->left, n->left->right, n->right);