cmd/gc: fix special-casing of the printed names of map internal structures.

Shaves 1% off of binary size.

update #6853

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/35940047

Author: randall77

src/cmd/gc/fmt.c

@@ -702,13 +702,17 @@ typefmt(Fmt *fp, Type *t)
 	case TSTRUCT:
 		// Format the bucket struct for map[x]y as map.bucket[x]y.
 		// This avoids a recursive print that generates very long names.
-		if(t->hmap != T) {
-			t = t->hmap;
-			return fmtprint(fp, "map.bucket[%T]%T", t->down, t->type);
-		}
-		if(t->hiter != T) {
-			t = t->hiter;
-			return fmtprint(fp, "map.iter[%T]%T", t->down, t->type);
+		if(t->map != T) {
+			if(t->map->bucket == t) {
+				return fmtprint(fp, "map.bucket[%T]%T", t->map->down, t->map->type);
+			}
+			if(t->map->hmap == t) {
+				return fmtprint(fp, "map.hdr[%T]%T", t->map->down, t->map->type);
+			}
+			if(t->map->hiter == t) {
+				return fmtprint(fp, "map.iter[%T]%T", t->map->down, t->map->type);
+			}
+			yyerror("unknown internal map type");
 		}
 
 		if(t->funarg) {

src/cmd/gc/go.h

@@ -191,6 +191,7 @@ struct	Type
 	Type*	bucket;		// internal type representing a hash bucket
 	Type*	hmap;		// internal type representing a Hmap (map header object)
 	Type*	hiter;		// internal type representing hash iterator state
+	Type*	map;		// link from the above 3 internal types back to the map type.
 
 	int32	maplineno;	// first use of TFORW as map key
 	int32	embedlineno;	// first use of TFORW as embedded type

src/cmd/gc/reflect.c

@@ -173,6 +173,7 @@ mapbucket(Type *t)
 	bucket->width = offset;
 	bucket->local = t->local;
 	t->bucket = bucket;
+	bucket->map = t;
 	return bucket;
 }
 
@@ -229,7 +230,7 @@ hmap(Type *t)
 	h->width = offset;
 	h->local = t->local;
 	t->hmap = h;
-	h->hmap = t;
+	h->map = t;
 	return h;
 }
 
@@ -308,7 +309,7 @@ hiter(Type *t)
 	if(off != 11 * widthptr)
 		yyerror("hash_iter size not correct %d %d", off, 11 * widthptr);
 	t->hiter = i;
-	i->hiter = t;
+	i->map = t;
 	return i;
 }