[dev.power64] cmd/9g: do not ignore move instructions even if from and to are samaddr()

Those moves might be significant (e.g. narrowing or widening): on Power64,
we don't distinguish between MOVWD and MOVW.

This fixes divmode.go and bug447.go.

LGTM=rsc
R=rsc, iant
CC=golang-codereviews
https://golang.org/cl/125200043

src/cmd/9g/gg.h

@@ -62,7 +62,6 @@ vlong	fieldoffset(Type*, Node*);
 void	sgen(Node*, Node*, int64);
 void	gmove(Node*, Node*);
 Prog*	gins(int, Node*, Node*);
-int	samaddr(Node*, Node*);
 void	naddr(Node*, Addr*, int);
 void	cgen_aret(Node*, Node*);
 int	componentgen(Node*, Node*);

src/cmd/9g/gsubr.c

@@ -1006,21 +1006,6 @@ hard:
 	return;
 }
 
-int
-samaddr(Node *f, Node *t)
-{
-	if(f->op != t->op)
-		return 0;
-
-	switch(f->op) {
-	case OREGISTER:
-		if(f->val.u.reg != t->val.u.reg)
-			break;
-		return 1;
-	}
-	return 0;
-}
-
 /*
  * generate one instruction:
  *	as f, t
@@ -1032,16 +1017,6 @@ gins(int as, Node *f, Node *t)
 	Prog *p;
 	Addr af, at;
 
-	switch(as) {
-	case AMOVW:
-	case AMOVD:
-	case AFMOVS:
-	case AFMOVD:
-		if(f != N && t != N && samaddr(f, t))
-			return nil;
-		break;
-	}
-
 	memset(&af, 0, sizeof af);
 	memset(&at, 0, sizeof at);
 	if(f != N)