[dev.power64] cmd/gc: handle thechar=='9', disable nilopt() for now

LGTM=rsc
R=rsc, iant, dave
CC=golang-codereviews
https://golang.org/cl/121630043

src/cmd/gc/pgen.c

@@ -428,7 +428,7 @@ allocauto(Prog* ptxt)
 		stksize = rnd(stksize, n->type->align);
 		if(haspointers(n->type))
 			stkptrsize = stksize;
-		if(thechar == '5')
+		if(thechar == '5' || thechar == '9')
 			stksize = rnd(stksize, widthptr);
 		if(stksize >= (1ULL<<31)) {
 			setlineno(curfn);
@@ -485,7 +485,7 @@ cgen_checknil(Node *n)
 		dump("checknil", n);
 		fatal("bad checknil");
 	}
-	if((thechar == '5' && n->op != OREGISTER) || !n->addable || n->op == OLITERAL) {
+	if(((thechar == '5' || thechar == '9') && n->op != OREGISTER) || !n->addable || n->op == OLITERAL) {
 		regalloc(&reg, types[tptr], n);
 		cgen(n, &reg);
 		gins(ACHECKNIL, &reg, N);

src/cmd/gc/popt.c

@@ -847,6 +847,10 @@ nilopt(Prog *firstp)
 	Graph *g;
 	int ncheck, nkill;
 
+	// TODO(minux): nilopt on power64 throw away seemly random segment of code.
+	if(thechar == '9')
+		return;
+
 	g = flowstart(firstp, sizeof(NilFlow));
 	if(g == nil)
 		return;