gc: implement goto restriction

Remove now-unnecessary zeroing of stack frames.

R=ken2
CC=golang-dev
https://golang.org/cl/4641044

src/cmd/5g/gobj.c

@@ -182,6 +182,8 @@ dumpfuncs(void)
 	// fix up pc
 	pcloc = 0;
 	for(pl=plist; pl!=nil; pl=pl->link) {
+		if(isblank(pl->name))
+			continue;
 		for(p=pl->firstpc; p!=P; p=p->link) {
 			p->loc = pcloc;
 			if(p->as != ADATA && p->as != AGLOBL)
@@ -191,6 +193,8 @@ dumpfuncs(void)
 
 	// put out functions
 	for(pl=plist; pl!=nil; pl=pl->link) {
+		if(isblank(pl->name))
+			continue;
 
 		if(debug['S']) {
 			s = S;

src/cmd/5g/gsubr.c

@@ -102,6 +102,21 @@ patch(Prog *p, Prog *to)
 	p->to.offset = to->loc;
 }
 
+Prog*
+unpatch(Prog *p)
+{
+	Prog *q;
+
+	if(p->to.type != D_BRANCH)
+		fatal("unpatch: not a branch");
+	if(p->to.branch == P)
+		fatal("unpatch: not patched");
+	q = p->to.branch;
+	p->to.branch = P;
+	p->to.offset = 0;
+	return q;
+}
+
 /*
  * start a new Prog list.
  */

src/cmd/6g/gobj.c

@@ -228,6 +228,8 @@ dumpfuncs(void)
 	// fix up pc
 	pcloc = 0;
 	for(pl=plist; pl!=nil; pl=pl->link) {
+		if(isblank(pl->name))
+			continue;
 		for(p=pl->firstpc; p!=P; p=p->link) {
 			p->loc = pcloc;
 			if(p->as != ADATA && p->as != AGLOBL)
@@ -237,6 +239,8 @@ dumpfuncs(void)
 
 	// put out functions
 	for(pl=plist; pl!=nil; pl=pl->link) {
+		if(isblank(pl->name))
+			continue;
 
 		if(debug['S']) {
 			s = S;

src/cmd/6g/gsubr.c

@@ -98,6 +98,19 @@ patch(Prog *p, Prog *to)
 	p->to.offset = to->loc;
 }
 
+Prog*
+unpatch(Prog *p)
+{
+	Prog *q;
+
+	if(p->to.type != D_BRANCH)
+		fatal("unpatch: not a branch");
+	q = p->to.branch;
+	p->to.branch = P;
+	p->to.offset = 0;
+	return q;
+}
+
 /*
  * start a new Prog list.
  */

src/cmd/8g/gobj.c

@@ -226,6 +226,8 @@ dumpfuncs(void)
 	// fix up pc
 	pcloc = 0;
 	for(pl=plist; pl!=nil; pl=pl->link) {
+		if(isblank(pl->name))
+			continue;
 		for(p=pl->firstpc; p!=P; p=p->link) {
 			p->loc = pcloc;
 			if(p->as != ADATA && p->as != AGLOBL)
@@ -235,6 +237,8 @@ dumpfuncs(void)
 
 	// put out functions
 	for(pl=plist; pl!=nil; pl=pl->link) {
+		if(isblank(pl->name))
+			continue;
 
 		if(debug['S']) {
 			s = S;

src/cmd/8g/gsubr.c

@@ -100,6 +100,21 @@ patch(Prog *p, Prog *to)
 	p->to.offset = to->loc;
 }
 
+Prog*
+unpatch(Prog *p)
+{
+	Prog *q;
+
+	if(p->to.type != D_BRANCH)
+		fatal("unpatch: not a branch");
+	if(p->to.branch == P)
+		fatal("unpatch: not patched");
+	q = p->to.branch;
+	p->to.branch = P;
+	p->to.offset = 0;
+	return q;
+}
+
 /*
  * start a new Prog list.
  */

src/cmd/gc/dcl.c

@@ -39,6 +39,7 @@ push(void)
 	Sym *d;
 
 	d = mal(sizeof(*d));
+	d->lastlineno = lineno;
 	d->link = dclstack;
 	dclstack = d;
 	return d;
@@ -60,6 +61,7 @@ void
 popdcl(void)
 {
 	Sym *d, *s;
+	int lno;
 
 //	if(dflag())
 //		print("revert\n");
@@ -68,7 +70,9 @@ popdcl(void)
 		if(d->name == nil)
 			break;
 		s = pkglookup(d->name, d->pkg);
+		lno = s->lastlineno;
 		dcopy(s, d);
+		d->lastlineno = lno;
 		if(dflag())
 			print("\t%L pop %S %p\n", lineno, s, s->def);
 	}
@@ -81,19 +85,12 @@ popdcl(void)
 void
 poptodcl(void)
 {
-	Sym *d, *s;
-
-	for(d=dclstack; d!=S; d=d->link) {
-		if(d->name == nil)
-			break;
-		s = pkglookup(d->name, d->pkg);
-		dcopy(s, d);
-		if(dflag())
-			print("\t%L pop %S\n", lineno, s);
-	}
-	if(d == S)
-		fatal("poptodcl: no mark");
-	dclstack = d;
+	// pop the old marker and push a new one
+	// (cannot reuse the existing one)
+	// because we use the markers to identify blocks
+	// for the goto restriction checks.
+	popdcl();
+	markdcl();
 }
 
 void
@@ -1241,10 +1238,7 @@ funccompile(Node *n, int isclosure)
 	stksize = 0;
 	dclcontext = PAUTO;
 	funcdepth = n->funcdepth + 1;
-	hasgoto = 0;
 	compile(n);
-	if(hasgoto)
-		clearstk();
 	curfn = nil;
 	funcdepth = 0;
 	dclcontext = PEXTERN;

src/cmd/gc/gen.c

@@ -11,6 +11,10 @@
 
 static void	cgen_dcl(Node *n);
 static void	cgen_proc(Node *n, int proc);
+static void checkgoto(Node*, Node*);
+
+static Label *labellist;
+static Label *lastlabel;
 
 Node*
 sysfunc(char *name)
@@ -80,71 +84,122 @@ clearlabels(void)
 	lastlabel = L;
 }
 
-static void
-newlab(int op, Node *nlab, Node *stmt)
+static Label*
+newlab(Node *n)
 {
-	Label *lab;
 	Sym *s;
-	int32 lno;
+	Label *lab;
+	
+	s = n->left->sym;
+	if((lab = s->label) == L) {
+		lab = mal(sizeof(*lab));
+		if(lastlabel == nil)
+			labellist = lab;
+		else
+			lastlabel->link = lab;
+		lastlabel = lab;
+		lab->sym = s;
+		s->label = lab;
+	}
 	
-	s = nlab->left->sym;
-	lno = nlab->left->lineno;
-
-	lab = mal(sizeof(*lab));
-	if(lastlabel == nil)
-		labellist = lab;
-	else
-		lastlabel->link = lab;
-	lastlabel = lab;
-
-	lab->lineno = lno;
-	lab->sym = s;
-	lab->op = op;
-	lab->label = pc;
-	lab->stmt = stmt;
-	if(op == OLABEL) {
-		if(s->label != L) {
-			lineno = lno;
-			yyerror("label %S already defined at %L", s, s->label->lineno);
-		} else
-			s->label = lab;
-	}	
+	if(n->op == OLABEL) {
+		if(lab->def != N)
+			yyerror("label %S already defined at %L", s, lab->def->lineno);
+		else
+			lab->def = n;
+	} else
+		lab->use = list(lab->use, n);
+
+	return lab;
 }
 
 void
 checklabels(void)
 {
-	Label *l;
-	Sym *s;
-	int lno;
+	Label *lab;
+	NodeList *l;
 
-	lno = lineno;
-	
-	// resolve goto using syms
-	for(l=labellist; l!=L; l=l->link) {
-		switch(l->op) {
-		case OGOTO:
-			s = l->sym;
-			if(s->label == L) {
-				lineno = l->lineno;
-				yyerror("label %S not defined", s);
-				break;
-			}
-			s->label->used = 1;
-			patch(l->label, s->label->label);
-			break;
+	for(lab=labellist; lab!=L; lab=lab->link) {
+		if(lab->def == N) {
+			for(l=lab->use; l; l=l->next)
+				yyerrorl(l->n->lineno, "label %S not defined", lab->sym);
+			continue;
 		}
+		if(lab->use == nil && !lab->used) {
+			yyerrorl(lab->def->lineno, "label %S defined and not used", lab->sym);
+			continue;
+		}
+		if(lab->gotopc != P)
+			fatal("label %S never resolved", lab->sym);
+		for(l=lab->use; l; l=l->next)
+			checkgoto(l->n, lab->def);
 	}
-	
-	// diagnose unused labels
-	for(l=labellist; l!=L; l=l->link) {
-		if(l->op == OLABEL && !l->used) {
-			lineno = l->lineno;
-			yyerror("label %S defined and not used", l->sym);
+}
+
+static void
+checkgoto(Node *from, Node *to)
+{
+	int nf, nt;
+	Sym *block, *dcl, *fs, *ts;
+	int lno;
+
+	if(from->sym == to->sym)
+		return;
+
+	nf = 0;
+	for(fs=from->sym; fs; fs=fs->link)
+		nf++;
+	nt = 0;
+	for(fs=to->sym; fs; fs=fs->link)
+		nt++;
+	fs = from->sym;
+	for(; nf > nt; nf--)
+		fs = fs->link;
+	if(fs != to->sym) {
+		lno = lineno;
+		setlineno(from);
+
+		// decide what to complain about.
+		// prefer to complain about 'into block' over declarations,
+		// so scan backward to find most recent block or else dcl.
+		block = S;
+		dcl = S;
+		ts = to->sym;
+		for(; nt > nf; nt--) {
+			if(ts->pkg == nil)
+				block = ts;
+			else
+				dcl = ts;
+			ts = ts->link;
 		}
+		while(ts != fs) {
+			if(ts->pkg == nil)
+				block = ts;
+			else
+				dcl = ts;
+			ts = ts->link;
+			fs = fs->link;
+		}
+
+		if(block)
+			yyerror("goto %S jumps into block starting at %L", from->left->sym, block->lastlineno);
+		else
+			yyerror("goto %S jumps over declaration of %S at %L", from->left->sym, dcl, dcl->lastlineno);
+		lineno = lno;
 	}
-	
-	lineno = lno;
+}
+
+static Label*
+stmtlabel(Node *n)
+{
+	Label *lab;
+
+	if(n->sym != S)
+	if((lab = n->sym->label) != L)
+	if(lab->def != N)
+	if(lab->def->right == n)
+		return lab;
+	return L;
 }
 
 /*
@@ -193,11 +248,6 @@ gen(Node *n)
 		break;
 
 	case OEMPTY:
-		// insert no-op so that
-		//	L:; for { }
-		// does not treat L as a label for the loop.
-		if(lastlabel != L && lastlabel->label == p3)
-			gused(N);
 		break;
 
 	case OBLOCK:
@@ -205,13 +255,41 @@ gen(Node *n)
 		break;
 
 	case OLABEL:
-		newlab(OLABEL, n, n->right);
+		lab = newlab(n);
+
+		// if there are pending gotos, resolve them all to the current pc.
+		for(p1=lab->gotopc; p1; p1=p2) {
+			p2 = unpatch(p1);
+			patch(p1, pc);
+		}
+		lab->gotopc = P;
+		if(lab->labelpc == P)
+			lab->labelpc = pc;
+
+		if(n->right) {
+			switch(n->right->op) {
+			case OFOR:
+			case OSWITCH:
+			case OSELECT:
+				// so stmtlabel can find the label
+				n->right->sym = lab->sym;
+			}
+		}
 		break;
 
 	case OGOTO:
-		hasgoto = 1;
-		newlab(OGOTO, n, N);
-		gjmp(P);
+		// if label is defined, emit jump to it.
+		// otherwise save list of pending gotos in lab->gotopc.
+		// the list is linked through the normal jump target field
+		// to avoid a second list.  (the jumps are actually still
+		// valid code, since they're just going to another goto
+		// to the same label.  we'll unwind it when we learn the pc
+		// of the label in the OLABEL case above.)
+		lab = newlab(n);
+		if(lab->labelpc != P)
+			gjmp(lab->labelpc);
+		else
+			lab->gotopc = gjmp(lab->gotopc);
 		break;
 
 	case OBREAK:
@@ -266,12 +344,10 @@ gen(Node *n)
 		continpc = pc;
 
 		// define break and continue labels
-		if((lab = lastlabel) != L && lab->label == p3 && lab->op == OLABEL && lab->stmt == n) {
+		if((lab = stmtlabel(n)) != L) {
 			lab->breakpc = breakpc;
 			lab->continpc = continpc;
-		} else
-			lab = L;
-
+		}
 		gen(n->nincr);				// contin:	incr
 		patch(p1, pc);				// test:
 		bgen(n->ntest, 0, breakpc);		//		if(!test) goto break
@@ -304,10 +380,8 @@ gen(Node *n)
 		breakpc = gjmp(P);		// break:	goto done
 
 		// define break label
-		if((lab = lastlabel) != L && lab->label == p3 && lab->op == OLABEL && lab->stmt == n)
+		if((lab = stmtlabel(n)) != L)
 			lab->breakpc = breakpc;
-		else
-			lab = L;
 
 		patch(p1, pc);				// test:
 		genlist(n->nbody);				//		switch(test) body
@@ -323,10 +397,8 @@ gen(Node *n)
 		breakpc = gjmp(P);		// break:	goto done
 
 		// define break label
-		if((lab = lastlabel) != L && lab->label == p3 && lab->op == OLABEL && lab->stmt == n)
+		if((lab = stmtlabel(n)) != L)
 			lab->breakpc = breakpc;
-		else
-			lab = L;
 
 		patch(p1, pc);				// test:
 		genlist(n->nbody);				//		select() body

src/cmd/gc/go.h

@@ -278,6 +278,7 @@ struct	Node
 	int32	iota;
 };
 #define	N	((Node*)0)
+EXTERN	int32	walkgen;
 
 struct	NodeList
 {
@@ -632,21 +633,20 @@ typedef struct	Prog Prog;
 
 struct	Label
 {
-	uchar	op;		// OGOTO/OLABEL
 	uchar	used;
 	Sym*	sym;
-	Node*	stmt;
-	Prog*	label;		// pointer to code
+	Node*	def;
+	NodeList*	use;
+	Label*	link;
+	
+	// for use during gen
+	Prog*	gotopc;	// pointer to unresolved gotos
+	Prog*	labelpc;	// pointer to code
 	Prog*	breakpc;	// pointer to code
 	Prog*	continpc;	// pointer to code
-	Label*	link;
-	int32	lineno;
 };
 #define	L	((Label*)0)
 
-EXTERN	Label*	labellist;
-EXTERN	Label*	lastlabel;
-
 /*
  * note this is the runtime representation
  * of the compilers arrays.
@@ -691,6 +691,7 @@ EXTERN	char*	infile;
 EXTERN	char*	outfile;
 EXTERN	Biobuf*	bout;
 EXTERN	int	nerrors;
+EXTERN	int	nsavederrors;
 EXTERN	int	nsyntaxerrors;
 EXTERN	int	safemode;
 EXTERN	char	namebuf[NSYMB];
@@ -913,8 +914,8 @@ Type*	pkgtype(Sym *s);
 void	allocparams(void);
 void	cgen_as(Node *nl, Node *nr);
 void	cgen_callmeth(Node *n, int proc);
-void	checklabels(void);
 void	clearlabels(void);
+void	checklabels(void);
 int	dotoffset(Node *n, int *oary, Node **nn);
 void	gen(Node *n);
 void	genlist(NodeList *l);
@@ -1132,6 +1133,7 @@ Type*	ptrto(Type *t);
 void*	remal(void *p, int32 on, int32 n);
 Sym*	restrictlookup(char *name, Pkg *pkg);
 Node*	safeexpr(Node *n, NodeList **init);
+void	saveerrors(void);
 Node*	cheapexpr(Node *n, NodeList **init);
 int32	setlineno(Node *n);
 void	setmaxarg(Type *t);
@@ -1252,11 +1254,10 @@ Plist*	newplist(void);
 Node*	nodarg(Type*, int);
 void	nopout(Prog*);
 void	patch(Prog*, Prog*);
+Prog*	unpatch(Prog*);
 void	zfile(Biobuf *b, char *p, int n);
 void	zhist(Biobuf *b, int line, vlong offset);
 void	zname(Biobuf *b, Sym *s, int t);
 void	data(void);
 void	text(void);
 
-EXTERN	int	hasgoto;
-void	clearstk(void);

src/cmd/gc/go.y

@@ -66,7 +66,7 @@ static void fixlbrace(int);
 %type	<node>	switch_stmt uexpr
 %type	<node>	xfndcl typedcl
 
-%type	<list>	xdcl fnbody fnres switch_body loop_body dcl_name_list
+%type	<list>	xdcl fnbody fnres loop_body dcl_name_list
 %type	<list>	new_name_list expr_list keyval_list braced_keyval_list expr_or_type_list xdcl_list
 %type	<list>	oexpr_list caseblock_list stmt_list oarg_type_list_ocomma arg_type_list
 %type	<list>	interfacedcl_list vardcl vardcl_list structdcl structdcl_list
@@ -449,7 +449,7 @@ case:
 		// will be converted to OCASE
 		// right will point to next case
 		// done in casebody()
-		poptodcl();
+		markdcl();
 		$$ = nod(OXCASE, N, N);
 		$$->list = $2;
 		if(typesw != N && typesw->right != N && (n=typesw->right->left) != N) {
@@ -468,7 +468,7 @@ case:
 		// will be converted to OCASE
 		// right will point to next case
 		// done in casebody()
-		poptodcl();
+		markdcl();
 		$$ = nod(OXCASE, N, N);
 		if($2->next == nil)
 			n = nod(OAS, $2->n, $4);
@@ -484,7 +484,7 @@ case:
 		// will be converted to OCASE
 		// right will point to next case
 		// done in casebody()
-		poptodcl();
+		markdcl();
 		$$ = nod(OXCASE, N, N);
 		$$->list = list1(colas($2, list1($4)));
 	}
@@ -492,7 +492,7 @@ case:
 	{
 		Node *n;
 
-		poptodcl();
+		markdcl();
 		$$ = nod(OXCASE, N, N);
 		if(typesw != N && typesw->right != N && (n=typesw->right->left) != N) {
 			// type switch - declare variable
@@ -514,17 +514,6 @@ compound_stmt:
 		popdcl();
 	}
 
-switch_body:
-	LBODY
-	{
-		markdcl();
-	}
-	caseblock_list '}'
-	{
-		$$ = $3;
-		popdcl();
-	}
-
 caseblock:
 	case
 	{
@@ -553,6 +542,7 @@ caseblock:
 			yyerror("missing statement after label");
 		$$ = $1;
 		$$->nbody = $3;
+		popdcl();
 	}
 
 caseblock_list:
@@ -674,11 +664,11 @@ switch_stmt:
 			n = N;
 		typesw = nod(OXXX, typesw, n);
 	}
-	switch_body
+	LBODY caseblock_list '}'
 	{
 		$$ = $3;
 		$$->op = OSWITCH;
-		$$->list = $5;
+		$$->list = $6;
 		typesw = typesw->left;
 		popdcl();
 	}
@@ -686,15 +676,13 @@ switch_stmt:
 select_stmt:
 	LSELECT
 	{
-		markdcl();
 		typesw = nod(OXXX, typesw, N);
 	}
-	switch_body
+	LBODY caseblock_list '}'
 	{
 		$$ = nod(OSELECT, N, N);
-		$$->list = $3;
+		$$->list = $4;
 		typesw = typesw->left;
-		popdcl();
 	}
 
 /*
@@ -1474,13 +1462,19 @@ non_dcl_stmt:
 		$$ = $1;
 		$$->nelse = list1($3);
 	}
-|	labelname ':' stmt
+|	labelname ':'
+	{
+		$1 = nod(OLABEL, $1, N);
+		$1->sym = dclstack;  // context, for goto restrictions
+	}
+	stmt
 	{
 		NodeList *l;
 
-		l = list1(nod(OLABEL, $1, $3));
-		if($3)
-			l = list(l, $3);
+		$1->right = $4;
+		l = list1($1);
+		if($4)
+			l = list(l, $4);
 		$$ = liststmt(l);
 	}
 |	LFALL
@@ -1507,6 +1501,7 @@ non_dcl_stmt:
 |	LGOTO new_name
 	{
 		$$ = nod(OGOTO, $2, N);
+		$$->sym = dclstack;  // context, for goto restrictions
 	}
 |	LRETURN oexpr_list
 	{

src/cmd/gc/lex.c

@@ -97,7 +97,7 @@ fault(int s)
 	// in the program, don't bother complaining
 	// about the seg fault too; let the user clean up
 	// the code and try again.
-	if(nerrors > 0)
+	if(nsavederrors + nerrors > 0)
 		errorexit();
 	fatal("fault");
 }
@@ -256,7 +256,10 @@ main(int argc, char *argv[])
 	for(l=xtop; l; l=l->next)
 		if(l->n->op == ODCLFUNC) {
 			curfn = l->n;
+			saveerrors();
 			typechecklist(l->n->nbody, Etop);
+			if(nerrors != 0)
+				l->n->nbody = nil;  // type errors; do not compile
 		}
 	curfn = nil;
 
@@ -264,7 +267,7 @@ main(int argc, char *argv[])
 		if(l->n->op == ODCLFUNC)
 			funccompile(l->n, 0);
 
-	if(nerrors == 0)
+	if(nsavederrors+nerrors == 0)
 		fninit(xtop);
 
 	while(closures) {
@@ -278,12 +281,12 @@ main(int argc, char *argv[])
 		if(l->n->op == ONAME)
 			typecheck(&l->n, Erv);
 
-	if(nerrors)
+	if(nerrors+nsavederrors)
 		errorexit();
 
 	dumpobj();
 
-	if(nerrors)
+	if(nerrors+nsavederrors)
 		errorexit();
 
 	flusherrors();
@@ -291,6 +294,13 @@ main(int argc, char *argv[])
 	return 0;
 }
 
+void
+saveerrors(void)
+{
+	nsavederrors += nerrors;
+	nerrors = 0;
+}
+
 static int
 arsize(Biobuf *b, char *name)
 {

src/cmd/gc/pgen.c

@@ -30,6 +30,8 @@ compile(Node *fn)
 	if(fn->nbody == nil)
 		return;
 
+	saveerrors();
+
 	// set up domain for labels
 	clearlabels();
 
@@ -53,7 +55,7 @@ compile(Node *fn)
 
 	hasdefer = 0;
 	walk(curfn);
-	if(nerrors != 0 || isblank(curfn->nname))
+	if(nerrors != 0)
 		goto ret;
 
 	allocparams();
@@ -67,7 +69,7 @@ compile(Node *fn)
 	setlineno(curfn);
 
 	nodconst(&nod1, types[TINT32], 0);
-	ptxt = gins(ATEXT, curfn->nname, &nod1);
+	ptxt = gins(ATEXT, isblank(curfn->nname) ? N : curfn->nname, &nod1);
 	afunclit(&ptxt->from);
 
 	ginit();

src/cmd/gc/typecheck.c

@@ -2716,6 +2716,11 @@ typecheckdef(Node *n)
 	default:
 		fatal("typecheckdef %O", n->op);
 
+	case OGOTO:
+	case OLABEL:
+		// not really syms
+		break;
+
 	case OLITERAL:
 		if(n->ntype != N) {
 			typecheck(&n->ntype, Etype);
@@ -2772,7 +2777,7 @@ typecheckdef(Node *n)
 		if(n->defn == N) {
 			if(n->etype != 0)	// like OPRINTN
 				break;
-			if(nerrors > 0) {
+			if(nsavederrors+nerrors > 0) {
 				// Can have undefined variables in x := foo
 				// that make x have an n->ndefn == nil.
 				// If there are other errors anyway, don't

test/fixedbugs/bug238.go

@@ -19,4 +19,3 @@ const h bool = false
 const i int = 2
 const j float64 = 5
 
-func main() { println(a, b, c, d, e, f, g) }

test/fixedbugs/bug274.go

@@ -25,6 +25,6 @@ func main() {
 		L1:  // ERROR "statement"
 	default:
 		     // correct since no semicolon is required before a '}'
-		L2:  // GCCGO_ERROR "not used"
+		L2:  // ERROR "not used"
 	}
 }

test/fixedbugs/bug344.go

-// $G $D/$F.go && $L $F.$A && ./$A.out || echo BUG: bug344
+// errchk $G -e $D/$F.go
 
 // Copyright 2011 The Go Authors.  All rights reserved.
 // Use of this source code is governed by a BSD-style
@@ -14,7 +14,9 @@ func main() {
 	i := 42
 	a := []*int{&i, &i, &i, &i}
 	x := a[0]
-	goto start
+	goto start  // ERROR "goto start jumps into block"
+	z := 1
+	_ = z
 	for _, x = range a {
 	start:
 		fmt.Sprint(*x)