runtime: record type information for hashtable internal structures.

Remove all hashtable-specific GC code.

Fixes bug 6119.

R=cshapiro, dvyukov, khr
CC=golang-dev
https://codereview.appspot.com/13078044

7 files changed, 164 insertions, 400 deletions

diff --git a/src/pkg/reflect/type.go b/src/pkg/reflect/type.go
index b513fee90..9686cfe0e 100644
--- a/src/pkg/reflect/type.go
+++ b/src/pkg/reflect/type.go
@@ -313,9 +313,11 @@ type interfaceType struct {
 
 // mapType represents a map type.
 type mapType struct {
-	rtype `reflect:"map"`
-	key   *rtype // map key type
-	elem  *rtype // map element (value) type
+	rtype  `reflect:"map"`
+	key    *rtype // map key type
+	elem   *rtype // map element (value) type
+	bucket *rtype // internal bucket structure
+	hmap   *rtype // internal map header
 }
 
 // ptrType represents a pointer type.
@@ -354,7 +356,6 @@ const (
 	_GC_ARRAY_START
 	_GC_ARRAY_NEXT
 	_GC_CALL
-	_GC_MAP_PTR
 	_GC_CHAN_PTR
 	_GC_STRING
 	_GC_EFACE
@@ -1400,11 +1401,11 @@ func cachePut(k cacheKey, t *rtype) Type {
 	return t
 }
 
-// garbage collection bytecode program for chan or map.
+// garbage collection bytecode program for chan.
 // See ../../cmd/gc/reflect.c:/^dgcsym1 and :/^dgcsym.
-type chanMapGC struct {
+type chanGC struct {
 	width uintptr // sizeof(map)
-	op    uintptr // _GC_MAP_PTR or _GC_CHAN_PTR
+	op    uintptr // _GC_CHAN_PTR
 	off   uintptr // 0
 	typ   *rtype  // map type
 	end   uintptr // _GC_END
@@ -1467,7 +1468,7 @@ func ChanOf(dir ChanDir, t Type) Type {
 	ch.uncommonType = nil
 	ch.ptrToThis = nil
 
-	ch.gc = unsafe.Pointer(&chanMapGC{
+	ch.gc = unsafe.Pointer(&chanGC{
 		width: ch.size,
 		op:    _GC_CHAN_PTR,
 		off:   0,
@@ -1521,17 +1522,11 @@ func MapOf(key, elem Type) Type {
 	mt.hash = fnv1(etyp.hash, 'm', byte(ktyp.hash>>24), byte(ktyp.hash>>16), byte(ktyp.hash>>8), byte(ktyp.hash))
 	mt.key = ktyp
 	mt.elem = etyp
+	mt.bucket = bucketOf(ktyp, etyp)
+	mt.hmap = hMapOf(mt.bucket)
 	mt.uncommonType = nil
 	mt.ptrToThis = nil
 
-	mt.gc = unsafe.Pointer(&chanMapGC{
-		width: mt.size,
-		op:    _GC_MAP_PTR,
-		off:   0,
-		typ:   &mt.rtype,
-		end:   _GC_END,
-	})
-
 	// INCORRECT. Uncomment to check that TestMapOfGC and TestMapOfGCValues
 	// fail when mt.gc is wrong.
 	//mt.gc = unsafe.Pointer(&badGC{width: mt.size, end: _GC_END})
@@ -1539,6 +1534,117 @@ func MapOf(key, elem Type) Type {
 	return cachePut(ckey, &mt.rtype)
 }
 
+// Make sure these routines stay in sync with ../../pkg/runtime/hashmap.c!
+// These types exist only for GC, so we only fill out GC relevant info.
+// Currently, that's just size and the GC program.  We also fill in string
+// for possible debugging use.
+const (
+	BUCKETSIZE = 8
+	MAXKEYSIZE = 128
+	MAXVALSIZE = 128
+)
+
+func bucketOf(ktyp, etyp *rtype) *rtype {
+	if ktyp.size > MAXKEYSIZE {
+		ktyp = PtrTo(ktyp).(*rtype)
+	}
+	if etyp.size > MAXVALSIZE {
+		etyp = PtrTo(etyp).(*rtype)
+	}
+	ptrsize := unsafe.Sizeof(uintptr(0))
+
+	gc := make([]uintptr, 1)                                       // first entry is size, filled in at the end
+	offset := BUCKETSIZE * unsafe.Sizeof(uint8(0))                 // topbits
+	gc = append(gc, _GC_PTR, offset, 0 /*self pointer set below*/) // overflow
+	offset += ptrsize
+
+	// keys
+	if ktyp.kind&kindNoPointers == 0 {
+		gc = append(gc, _GC_ARRAY_START, offset, BUCKETSIZE, ktyp.size)
+		gc = appendGCProgram(gc, ktyp)
+		gc = append(gc, _GC_ARRAY_NEXT)
+	}
+	offset += BUCKETSIZE * ktyp.size
+
+	// values
+	if etyp.kind&kindNoPointers == 0 {
+		gc = append(gc, _GC_ARRAY_START, offset, BUCKETSIZE, etyp.size)
+		gc = appendGCProgram(gc, etyp)
+		gc = append(gc, _GC_ARRAY_NEXT)
+	}
+	offset += BUCKETSIZE * etyp.size
+
+	gc = append(gc, _GC_END)
+	gc[0] = offset
+	gc[3] = uintptr(unsafe.Pointer(&gc[0])) // set self pointer
+
+	b := new(rtype)
+	b.size = offset
+	b.gc = unsafe.Pointer(&gc[0])
+	s := "bucket(" + *ktyp.string + "," + *etyp.string + ")"
+	b.string = &s
+	return b
+}
+
+// Take the GC program for "t" and append it to the GC program "gc".
+func appendGCProgram(gc []uintptr, t *rtype) []uintptr {
+	p := t.gc
+	p = unsafe.Pointer(uintptr(p) + unsafe.Sizeof(uintptr(0))) // skip size
+loop:
+	for {
+		var argcnt int
+		switch *(*uintptr)(p) {
+		case _GC_END:
+			// Note: _GC_END not included in append
+			break loop
+		case _GC_ARRAY_NEXT:
+			argcnt = 0
+		case _GC_APTR, _GC_STRING, _GC_EFACE, _GC_IFACE:
+			argcnt = 1
+		case _GC_PTR, _GC_CALL, _GC_CHAN_PTR, _GC_SLICE:
+			argcnt = 2
+		case _GC_ARRAY_START, _GC_REGION:
+			argcnt = 3
+		default:
+			panic("unknown GC program op for " + *t.string + ": " + strconv.FormatUint(*(*uint64)(p), 10))
+		}
+		for i := 0; i < argcnt+1; i++ {
+			gc = append(gc, *(*uintptr)(p))
+			p = unsafe.Pointer(uintptr(p) + unsafe.Sizeof(uintptr(0)))
+		}
+	}
+	return gc
+}
+func hMapOf(bucket *rtype) *rtype {
+	ptrsize := unsafe.Sizeof(uintptr(0))
+
+	// make gc program & compute hmap size
+	gc := make([]uintptr, 1)           // first entry is size, filled in at the end
+	offset := unsafe.Sizeof(uint(0))   // count
+	offset += unsafe.Sizeof(uint32(0)) // flags
+	offset += unsafe.Sizeof(uint32(0)) // hash0
+	offset += unsafe.Sizeof(uint8(0))  // B
+	offset += unsafe.Sizeof(uint8(0))  // keysize
+	offset += unsafe.Sizeof(uint8(0))  // valuesize
+	offset = (offset + 1) / 2 * 2
+	offset += unsafe.Sizeof(uint16(0)) // bucketsize
+	offset = (offset + ptrsize - 1) / ptrsize * ptrsize
+	gc = append(gc, _GC_PTR, offset, uintptr(bucket.gc)) // buckets
+	offset += ptrsize
+	gc = append(gc, _GC_PTR, offset, uintptr(bucket.gc)) // oldbuckets
+	offset += ptrsize
+	offset += ptrsize // nevacuate
+	gc = append(gc, _GC_END)
+	gc[0] = offset
+
+	h := new(rtype)
+	h.size = offset
+	h.gc = unsafe.Pointer(&gc[0])
+	s := "hmap(" + *bucket.string + ")"
+	h.string = &s
+	return h
+}
+
 // garbage collection bytecode program for slice of non-zero-length values.
 // See ../../cmd/gc/reflect.c:/^dgcsym1 and :/^dgcsym.
 type sliceGC struct {
diff --git a/src/pkg/runtime/hashmap.c b/src/pkg/runtime/hashmap.c
index 36cbda5ab..244885be1 100644
--- a/src/pkg/runtime/hashmap.c
+++ b/src/pkg/runtime/hashmap.c
@@ -75,6 +75,8 @@
 typedef struct Bucket Bucket;
 struct Bucket
 {
+	// Note: the format of the Bucket is encoded in ../../cmd/gc/reflect.c and
+	// ../reflect/type.go.  Don't change this structure without also changing that code!
 	uint8  tophash[BUCKETSIZE]; // top 8 bits of hash of each entry (0 = empty)
 	Bucket *overflow;           // overflow bucket, if any
 	byte   data[1];             // BUCKETSIZE keys followed by BUCKETSIZE values
@@ -90,14 +92,13 @@ struct Bucket
 #define evacuated(b) (((uintptr)(b)->overflow & 1) != 0)
 #define overflowptr(b) ((Bucket*)((uintptr)(b)->overflow & ~(uintptr)1))
 
-// Initialize bucket to the empty state.  This only works if BUCKETSIZE==8!
-#define clearbucket(b) { *(uint64*)((b)->tophash) = 0; (b)->overflow = nil; }
-
 struct Hmap
 {
+	// Note: the format of the Hmap is encoded in ../../cmd/gc/reflect.c and
+	// ../reflect/type.go.  Don't change this structure without also changing that code!
 	uintgo  count;        // # live cells == size of map.  Must be first (used by len() builtin)
 	uint32  flags;
-	uint32 hash0;        // hash seed
+	uint32  hash0;        // hash seed
 	uint8   B;            // log_2 of # of buckets (can hold up to LOAD * 2^B items)
 	uint8   keysize;      // key size in bytes
 	uint8   valuesize;    // value size in bytes
@@ -115,8 +116,6 @@ enum
 	IndirectValue = 2,  // storing pointers to values
 	Iterator = 4,       // there may be an iterator using buckets
 	OldIterator = 8,    // there may be an iterator using oldbuckets
-	CanFreeBucket = 16, // ok to free buckets
-	CanFreeKey = 32,    // keys are indirect and ok to free keys
 };
 
 // Macros for dereferencing indirect keys
@@ -209,17 +208,15 @@ hash_init(MapType *t, Hmap *h, uint32 hint)
 {
 	uint8 B;
 	byte *buckets;
-	uintptr i;
 	uintptr keysize, valuesize, bucketsize;
 	uint8 flags;
-	Bucket *b;
 
-	flags = CanFreeBucket;
+	flags = 0;
 
 	// figure out how big we have to make everything
 	keysize = t->key->size;
 	if(keysize > MAXKEYSIZE) {
-		flags |= IndirectKey | CanFreeKey;
+		flags |= IndirectKey;
 		keysize = sizeof(byte*);
 	}
 	valuesize = t->elem->size;
@@ -241,8 +238,6 @@ hash_init(MapType *t, Hmap *h, uint32 hint)
 		runtime·throw("value size not a multiple of value align");
 	if(BUCKETSIZE < 8)
 		runtime·throw("bucketsize too small for proper alignment");
-	if(BUCKETSIZE != 8)
-		runtime·throw("must redo clearbucket");
 	if(sizeof(void*) == 4 && t->key->align > 4)
 		runtime·throw("need padding in bucket (key)");
 	if(sizeof(void*) == 4 && t->elem->align > 4)
@@ -260,16 +255,10 @@ hash_init(MapType *t, Hmap *h, uint32 hint)
 		// done lazily later.
 		buckets = nil;
 	} else {
-		buckets = runtime·mallocgc(bucketsize << B, 0, FlagNoZero);
-		for(i = 0; i < (uintptr)1 << B; i++) {
-			b = (Bucket*)(buckets + i * bucketsize);
-			clearbucket(b);
-		}
+		buckets = runtime·mallocgc(bucketsize << B, (uintptr)t->bucket | TypeInfo_Array, 0);
 	}
 
 	// initialize Hmap
-	// Note: we save all these stores to the end so gciter doesn't see
-	// a partially initialized map.
 	h->count = 0;
 	h->B = B;
 	h->flags = flags;
@@ -300,19 +289,16 @@ evacuate(MapType *t, Hmap *h, uintptr oldbucket)
 	uintptr i;
 	byte *k, *v;
 	byte *xk, *yk, *xv, *yv;
-	byte *ob;
 
 	b = (Bucket*)(h->oldbuckets + oldbucket * h->bucketsize);
 	newbit = (uintptr)1 << (h->B - 1);
 
 	if(!evacuated(b)) {
 		// TODO: reuse overflow buckets instead of using new ones, if there
-		// is no iterator using the old buckets.  (If CanFreeBuckets and !OldIterator.)
+		// is no iterator using the old buckets.  (If !OldIterator.)
 
 		x = (Bucket*)(h->buckets + oldbucket * h->bucketsize);
 		y = (Bucket*)(h->buckets + (oldbucket + newbit) * h->bucketsize);
-		clearbucket(x);
-		clearbucket(y);
 		xi = 0;
 		yi = 0;
 		xk = x->data;
@@ -331,8 +317,7 @@ evacuate(MapType *t, Hmap *h, uintptr oldbucket)
 				if((hash & newbit) == 0) {
 					if(xi == BUCKETSIZE) {
 						if(checkgc) mstats.next_gc = mstats.heap_alloc;
-						newx = runtime·mallocgc(h->bucketsize, 0, FlagNoZero);
-						clearbucket(newx);
+						newx = runtime·mallocgc(h->bucketsize, (uintptr)t->bucket, 0);
 						x->overflow = newx;
 						x = newx;
 						xi = 0;
@@ -356,8 +341,7 @@ evacuate(MapType *t, Hmap *h, uintptr oldbucket)
 				} else {
 					if(yi == BUCKETSIZE) {
 						if(checkgc) mstats.next_gc = mstats.heap_alloc;
-						newy = runtime·mallocgc(h->bucketsize, 0, FlagNoZero);
-						clearbucket(newy);
+						newy = runtime·mallocgc(h->bucketsize, (uintptr)t->bucket, 0);
 						y->overflow = newy;
 						y = newy;
 						yi = 0;
@@ -389,35 +373,18 @@ evacuate(MapType *t, Hmap *h, uintptr oldbucket)
 			b = nextb;
 		} while(b != nil);
 
-		// Free old overflow buckets as much as we can.
-		if((h->flags & OldIterator) == 0) {
-			b = (Bucket*)(h->oldbuckets + oldbucket * h->bucketsize);
-			if((h->flags & CanFreeBucket) != 0) {
-				while((nextb = overflowptr(b)) != nil) {
-					b->overflow = nextb->overflow;
-					runtime·free(nextb);
-				}
-			} else {
-				// can't explicitly free overflow buckets, but at least
-				// we can unlink them.
-				b->overflow = (Bucket*)1;
-			}
-		}
+		// Unlink the overflow buckets to help GC.
+		b = (Bucket*)(h->oldbuckets + oldbucket * h->bucketsize);
+		if((h->flags & OldIterator) == 0)
+			b->overflow = (Bucket*)1;
 	}
 
 	// advance evacuation mark
 	if(oldbucket == h->nevacuate) {
 		h->nevacuate = oldbucket + 1;
-		if(oldbucket + 1 == newbit) { // newbit == # of oldbuckets
+		if(oldbucket + 1 == newbit) // newbit == # of oldbuckets
 			// free main bucket array
-			if((h->flags & (OldIterator | CanFreeBucket)) == CanFreeBucket) {
-				ob = h->oldbuckets;
-				h->oldbuckets = nil;
-				runtime·free(ob);
-			} else {
-				h->oldbuckets = nil;
-			}
-		}
+			h->oldbuckets = nil;
 	}
 	if(docheck)
 		check(t, h);
@@ -452,14 +419,10 @@ hash_grow(MapType *t, Hmap *h)
 	old_buckets = h->buckets;
 	// NOTE: this could be a big malloc, but since we don't need zeroing it is probably fast.
 	if(checkgc) mstats.next_gc = mstats.heap_alloc;
-	new_buckets = runtime·mallocgc((uintptr)h->bucketsize << (h->B + 1), 0, FlagNoZero);
+	new_buckets = runtime·mallocgc((uintptr)h->bucketsize << (h->B + 1), (uintptr)t->bucket | TypeInfo_Array, 0);
 	flags = (h->flags & ~(Iterator | OldIterator));
-	if((h->flags & Iterator) != 0) {
+	if((h->flags & Iterator) != 0)
 		flags |= OldIterator;
-		// We can't free indirect keys any more, as
-		// they are potentially aliased across buckets.
-		flags &= ~CanFreeKey;
-	}
 
 	// commit the grow (atomic wrt gc)
 	h->B++;
@@ -614,11 +577,8 @@ hash_insert(MapType *t, Hmap *h, void *key, void *value)
 		check(t, h);
 	hash = h->hash0;
 	t->key->alg->hash(&hash, t->key->size, key);
-	if(h->buckets == nil) {
-		h->buckets = runtime·mallocgc(h->bucketsize, 0, FlagNoZero);
-		b = (Bucket*)(h->buckets);
-		clearbucket(b);
-	}
+	if(h->buckets == nil)
+		h->buckets = runtime·mallocgc(h->bucketsize, (uintptr)t->bucket | TypeInfo_Array, 0);
 
  again:
 	bucket = hash & (((uintptr)1 << h->B) - 1);
@@ -665,8 +625,7 @@ hash_insert(MapType *t, Hmap *h, void *key, void *value)
 	if(inserti == nil) {
 		// all current buckets are full, allocate a new one.
 		if(checkgc) mstats.next_gc = mstats.heap_alloc;
-		newb = runtime·mallocgc(h->bucketsize, 0, FlagNoZero);
-		clearbucket(newb);
+		newb = runtime·mallocgc(h->bucketsize, (uintptr)t->bucket, 0);
 		b->overflow = newb;
 		inserti = newb->tophash;
 		insertk = newb->data;
@@ -676,13 +635,13 @@ hash_insert(MapType *t, Hmap *h, void *key, void *value)
 	// store new key/value at insert position
 	if((h->flags & IndirectKey) != 0) {
 		if(checkgc) mstats.next_gc = mstats.heap_alloc;
-		kmem = runtime·mallocgc(t->key->size, 0, FlagNoZero);
+		kmem = runtime·mallocgc(t->key->size, (uintptr)t->key, 0);
 		*(byte**)insertk = kmem;
 		insertk = kmem;
 	}
 	if((h->flags & IndirectValue) != 0) {
 		if(checkgc) mstats.next_gc = mstats.heap_alloc;
-		vmem = runtime·mallocgc(t->elem->size, 0, FlagNoZero);
+		vmem = runtime·mallocgc(t->elem->size, (uintptr)t->elem, 0);
 		*(byte**)insertv = vmem;
 		insertv = vmem;
 	}
@@ -726,22 +685,20 @@ hash_remove(MapType *t, Hmap *h, void *key)
 			if(!eq)
 				continue;
 
-			if((h->flags & CanFreeKey) != 0) {
-				k = *(byte**)k;
+			if((h->flags & IndirectKey) != 0) {
+				*(byte**)k = nil;
+			} else {
+				t->key->alg->copy(t->key->size, k, nil);
 			}
 			if((h->flags & IndirectValue) != 0) {
-				v = *(byte**)v;
+				*(byte**)v = nil;
+			} else {
+				t->elem->alg->copy(t->elem->size, v, nil);
 			}
 
 			b->tophash[i] = 0;
 			h->count--;
 			
-			if((h->flags & CanFreeKey) != 0) {
-				runtime·free(k);
-			}
-			if((h->flags & IndirectValue) != 0) {
-				runtime·free(v);
-			}
 			// TODO: consolidate buckets if they are mostly empty
 			// can only consolidate if there are no live iterators at this size.
 			if(docheck)
@@ -804,7 +761,7 @@ hash_iter_init(MapType *t, Hmap *h, struct hash_iter *it)
 	it->bptr = nil;
 
 	// Remember we have an iterator.
-	// Can run concurrently with another hash_iter_init() and with reflect·mapiterinit().
+	// Can run concurrently with another hash_iter_init().
 	for(;;) {
 		old = h->flags;
 		if((old&(Iterator|OldIterator)) == (Iterator|OldIterator))
@@ -944,157 +901,6 @@ next:
 	goto next;
 }
 
-
-#define PHASE_BUCKETS      0
-#define PHASE_OLD_BUCKETS  1
-#define PHASE_TABLE        2
-#define PHASE_OLD_TABLE    3
-#define PHASE_DONE         4
-
-// Initialize the iterator.
-// Returns false if Hmap contains no pointers (in which case the iterator is not initialized).
-bool
-hash_gciter_init (Hmap *h, struct hash_gciter *it)
-{
-	// GC during map initialization or on an empty map.
-	if(h->buckets == nil)
-		return false;
-
-	it->h = h;
-	it->phase = PHASE_BUCKETS;
-	it->bucket = 0;
-	it->b = nil;
-
-	// TODO: finish evacuating oldbuckets so that we can collect
-	// oldbuckets?  We don't want to keep a partially evacuated
-	// table around forever, so each gc could make at least some
-	// evacuation progress.  Need to be careful about concurrent
-	// access if we do concurrent gc.  Even if not, we don't want
-	// to make the gc pause any longer than it has to be.
-
-	return true;
-}
-
-// Returns true and fills *data with internal structure/key/value data,
-// or returns false if the iterator has terminated.
-// Ugh, this interface is really annoying.  I want a callback fn!
-bool
-hash_gciter_next(struct hash_gciter *it, struct hash_gciter_data *data)
-{
-	Hmap *h;
-	uintptr bucket, oldbucket;
-	Bucket *b, *oldb;
-	uintptr i;
-	byte *k, *v;
-
-	h = it->h;
-	bucket = it->bucket;
-	b = it->b;
-	i = it->i;
-
-	data->st = nil;
-	data->key_data = nil;
-	data->val_data = nil;
-	data->indirectkey = (h->flags & IndirectKey) != 0;
-	data->indirectval = (h->flags & IndirectValue) != 0;
-
-next:
-	switch (it->phase) {
-	case PHASE_BUCKETS:
-		if(b != nil) {
-			k = b->data + h->keysize * i;
-			v = b->data + h->keysize * BUCKETSIZE + h->valuesize * i;
-			for(; i < BUCKETSIZE; i++, k += h->keysize, v += h->valuesize) {
-				if(b->tophash[i] != 0) {
-					data->key_data = k;
-					data->val_data = v;
-					it->bucket = bucket;
-					it->b = b;
-					it->i = i + 1;
-					return true;
-				}
-			}
-			b = b->overflow;
-			if(b != nil) {
-				data->st = (byte*)b;
-				it->bucket = bucket;
-				it->b = b;
-				it->i = 0;
-				return true;
-			}
-		}
-		while(bucket < ((uintptr)1 << h->B)) {
-			if(h->oldbuckets != nil) {
-				oldbucket = bucket & (((uintptr)1 << (h->B - 1)) - 1);
-				oldb = (Bucket*)(h->oldbuckets + oldbucket * h->bucketsize);
-				if(!evacuated(oldb)) {
-					// new bucket isn't valid yet
-					bucket++;
-					continue;
-				}
-			}
-			b = (Bucket*)(h->buckets + bucket * h->bucketsize);
-			i = 0;
-			bucket++;
-			goto next;
-		}
-		it->phase = PHASE_OLD_BUCKETS;
-		bucket = 0;
-		b = nil;
-		goto next;
-	case PHASE_OLD_BUCKETS:
-		if(h->oldbuckets == nil) {
-			it->phase = PHASE_TABLE;
-			goto next;
-		}
-		if(b != nil) {
-			k = b->data + h->keysize * i;
-			v = b->data + h->keysize * BUCKETSIZE + h->valuesize * i;
-			for(; i < BUCKETSIZE; i++, k += h->keysize, v += h->valuesize) {
-				if(b->tophash[i] != 0) {
-					data->key_data = k;
-					data->val_data = v;
-					it->bucket = bucket;
-					it->b = b;
-					it->i = i + 1;
-					return true;
-				}
-			}
-			b = overflowptr(b);
-			if(b != nil) {
-				data->st = (byte*)b;
-				it->bucket = bucket;
-				it->b = b;
-				it->i = 0;
-				return true;
-			}
-		}
-		if(bucket < ((uintptr)1 << (h->B - 1))) {
-			b = (Bucket*)(h->oldbuckets + bucket * h->bucketsize);
-			bucket++;
-			i = 0;
-			goto next;
-		}
-		it->phase = PHASE_TABLE;
-		goto next;
-	case PHASE_TABLE:
-		it->phase = PHASE_OLD_TABLE;
-		data->st = h->buckets;
-		return true;
-	case PHASE_OLD_TABLE:
-		it->phase = PHASE_DONE;
-		if(h->oldbuckets != nil) {
-			data->st = h->oldbuckets;
-			return true;
-		} else {
-			goto next;
-		}
-	}
-	if(it->phase != PHASE_DONE)
-		runtime·throw("bad phase at done");
-	return false;
-}
-
 //
 /// interfaces to go runtime
 //
@@ -1123,7 +929,7 @@ runtime·makemap_c(MapType *typ, int64 hint)
 	if(key->alg->hash == runtime·nohash)
 		runtime·throw("runtime.makemap: unsupported map key type");
 
-	h = runtime·mallocgc(sizeof(*h), (uintptr)typ | TypeInfo_Map, 0);
+	h = runtime·mallocgc(sizeof(*h), (uintptr)typ->hmap, 0);
 	hash_init(typ, h, hint);
 
 	// these calculations are compiler dependent.
@@ -1387,26 +1193,6 @@ runtime·mapiterinit(MapType *t, Hmap *h, struct hash_iter *it)
 void
 reflect·mapiterinit(MapType *t, Hmap *h, struct hash_iter *it)
 {
-	uint32 old, new;
-
-	if(h != nil && t->key->size > sizeof(void*)) {
-		// reflect·mapiterkey returns pointers to key data,
-		// and reflect holds them, so we cannot free key data
-		// eagerly anymore.
-		// Can run concurrently with another reflect·mapiterinit() and with hash_iter_init().
-		for(;;) {
-			old = h->flags;
-			if(old & IndirectKey)
-				new = old & ~CanFreeKey;
-			else
-				new = old & ~CanFreeBucket;
-			if(new == old)
-				break;
-			if(runtime·cas(&h->flags, old, new))
-				break;
-		}
-	}
-
 	it = runtime·mal(sizeof *it);
 	FLUSH(&it);
 	runtime·mapiterinit(t, h, it);
diff --git a/src/pkg/runtime/hashmap.h b/src/pkg/runtime/hashmap.h
index 2988417f6..024018d5a 100644
--- a/src/pkg/runtime/hashmap.h
+++ b/src/pkg/runtime/hashmap.h
@@ -2,32 +2,3 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-struct Hmap;		/* opaque */
-
-/* Used by the garbage collector */
-struct hash_gciter
-{
-	Hmap *h;
-	int32 phase;
-	uintptr bucket;
-	struct Bucket *b;
-	uintptr i;
-};
-
-// this data is used by the garbage collector to keep the map's
-// internal structures from being reclaimed.  The iterator must
-// return in st every live object (ones returned by mallocgc) so
-// that those objects won't be collected, and it must return
-// every key & value in key_data/val_data so they can get scanned
-// for pointers they point to.  Note that if you malloc storage
-// for keys and values, you need to do both.
-struct hash_gciter_data
-{
-	uint8 *st;			/* internal structure, or nil */
-	uint8 *key_data;		/* key data, or nil */
-	uint8 *val_data;		/* value data, or nil */
-	bool indirectkey;		/* storing pointers to keys */
-	bool indirectval;		/* storing pointers to values */
-};
-bool hash_gciter_init (struct Hmap *h, struct hash_gciter *it);
-bool hash_gciter_next (struct hash_gciter *it, struct hash_gciter_data *data);
diff --git a/src/pkg/runtime/malloc.h b/src/pkg/runtime/malloc.h
index c0f5a8fa6..e0dc50f3a 100644
--- a/src/pkg/runtime/malloc.h
+++ b/src/pkg/runtime/malloc.h
@@ -487,8 +487,7 @@ enum
 {
 	TypeInfo_SingleObject = 0,
 	TypeInfo_Array = 1,
-	TypeInfo_Map = 2,
-	TypeInfo_Chan = 3,
+	TypeInfo_Chan = 2,
 
 	// Enables type information at the end of blocks allocated from heap	
 	DebugTypeAtBlockEnd = 0,
diff --git a/src/pkg/runtime/mgc0.c b/src/pkg/runtime/mgc0.c
index 14623040d..045202915 100644
--- a/src/pkg/runtime/mgc0.c
+++ b/src/pkg/runtime/mgc0.c
@@ -176,7 +176,6 @@ static struct {
 
 enum {
 	GC_DEFAULT_PTR = GC_NUM_INSTR,
-	GC_MAP_NEXT,
 	GC_CHAN,
 
 	GC_NUM_INSTR2
@@ -580,9 +579,6 @@ flushobjbuf(Obj *objbuf, Obj **objbufpos, Obj **_wp, Workbuf **_wbuf, uintptr *_
 // Program that scans the whole block and treats every block element as a potential pointer
 static uintptr defaultProg[2] = {PtrSize, GC_DEFAULT_PTR};
 
-// Hashmap iterator program
-static uintptr mapProg[2] = {0, GC_MAP_NEXT};
-
 // Hchan program
 static uintptr chanProg[2] = {0, GC_CHAN};
 
@@ -622,8 +618,11 @@ checkptr(void *obj, uintptr objti)
 	}
 	tisize = *(uintptr*)objti;
 	// Sanity check for object size: it should fit into the memory block.
-	if((byte*)obj + tisize > objstart + s->elemsize)
+	if((byte*)obj + tisize > objstart + s->elemsize) {
+		runtime·printf("object of type '%S' at %p/%p does not fit in block %p/%p\n",
+			       *t->string, obj, tisize, objstart, s->elemsize);
 		runtime·throw("invalid gc type info");
+	}
 	if(obj != objstart)
 		return;
 	// If obj points to the beginning of the memory block,
@@ -639,7 +638,7 @@ checkptr(void *obj, uintptr objti)
 		for(j = 1; pc1[j] != GC_END && pc2[j] != GC_END; j++) {
 			if(pc1[j] != pc2[j]) {
 				runtime·printf("invalid gc type info for '%s' at %p, type info %p, block info %p\n",
-					t->string ? (int8*)t->string->str : (int8*)"?", j, pc1[j], pc2[j]);
+					       t->string ? (int8*)t->string->str : (int8*)"?", j, pc1[j], pc2[j]);
 				runtime·throw("invalid gc type info");
 			}
 		}
@@ -662,7 +661,7 @@ scanblock(Workbuf *wbuf, Obj *wp, uintptr nobj, bool keepworking)
 	byte *b, *arena_start, *arena_used;
 	uintptr n, i, end_b, elemsize, size, ti, objti, count, type;
 	uintptr *pc, precise_type, nominal_size;
-	uintptr *map_ret, mapkey_size, mapval_size, mapkey_ti, mapval_ti, *chan_ret, chancap;
+	uintptr *chan_ret, chancap;
 	void *obj;
 	Type *t;
 	Slice *sliceptr;
@@ -672,11 +671,6 @@ scanblock(Workbuf *wbuf, Obj *wp, uintptr nobj, bool keepworking)
 	Obj *objbuf, *objbuf_end, *objbufpos;
 	Eface *eface;
 	Iface *iface;
-	Hmap *hmap;
-	MapType *maptype;
-	bool mapkey_kind, mapval_kind;
-	struct hash_gciter map_iter;
-	struct hash_gciter_data d;
 	Hchan *chan;
 	ChanType *chantype;
 
@@ -705,10 +699,6 @@ scanblock(Workbuf *wbuf, Obj *wp, uintptr nobj, bool keepworking)
 	objbufpos = objbuf;
 
 	// (Silence the compiler)
-	map_ret = nil;
-	mapkey_size = mapval_size = 0;
-	mapkey_kind = mapval_kind = false;
-	mapkey_ti = mapval_ti = 0;
 	chan = nil;
 	chantype = nil;
 	chan_ret = nil;
@@ -777,23 +767,6 @@ scanblock(Workbuf *wbuf, Obj *wp, uintptr nobj, bool keepworking)
 					stack_top.elemsize = pc[0];
 					stack_top.loop_or_ret = pc+1;
 					break;
-				case TypeInfo_Map:
-					hmap = (Hmap*)b;
-					maptype = (MapType*)t;
-					if(hash_gciter_init(hmap, &map_iter)) {
-						mapkey_size = maptype->key->size;
-						mapkey_kind = maptype->key->kind;
-						mapkey_ti   = (uintptr)maptype->key->gc | PRECISE;
-						mapval_size = maptype->elem->size;
-						mapval_kind = maptype->elem->kind;
-						mapval_ti   = (uintptr)maptype->elem->gc | PRECISE;
-
-						map_ret = nil;
-						pc = mapProg;
-					} else {
-						goto next_block;
-					}
-					break;
 				case TypeInfo_Chan:
 					chan = (Hchan*)b;
 					chantype = (ChanType*)t;
@@ -994,77 +967,6 @@ scanblock(Workbuf *wbuf, Obj *wp, uintptr nobj, bool keepworking)
 			pc = (uintptr*)((byte*)pc + *(int32*)(pc+2));  // target of the CALL instruction
 			continue;
 
-		case GC_MAP_PTR:
-			hmap = *(Hmap**)(stack_top.b + pc[1]);
-			if(hmap == nil) {
-				pc += 3;
-				continue;
-			}
-			if(markonly(hmap)) {
-				maptype = (MapType*)pc[2];
-				if(hash_gciter_init(hmap, &map_iter)) {
-					mapkey_size = maptype->key->size;
-					mapkey_kind = maptype->key->kind;
-					mapkey_ti   = (uintptr)maptype->key->gc | PRECISE;
-					mapval_size = maptype->elem->size;
-					mapval_kind = maptype->elem->kind;
-					mapval_ti   = (uintptr)maptype->elem->gc | PRECISE;
-
-					// Start mapProg.
-					map_ret = pc+3;
-					pc = mapProg+1;
-				} else {
-					pc += 3;
-				}
-			} else {
-				pc += 3;
-			}
-			continue;
-
-		case GC_MAP_NEXT:
-			// Add all keys and values to buffers, mark all subtables.
-			while(hash_gciter_next(&map_iter, &d)) {
-				// buffers: reserve space for 2 objects.
-				if(ptrbufpos+2 >= ptrbuf_end)
-					flushptrbuf(ptrbuf, &ptrbufpos, &wp, &wbuf, &nobj);
-				if(objbufpos+2 >= objbuf_end)
-					flushobjbuf(objbuf, &objbufpos, &wp, &wbuf, &nobj);
-
-				if(d.st != nil)
-					markonly(d.st);
-
-				if(d.key_data != nil) {
-					if(!(mapkey_kind & KindNoPointers) || d.indirectkey) {
-						if(!d.indirectkey)
-							*objbufpos++ = (Obj){d.key_data, mapkey_size, mapkey_ti};
-						else {
-							if(Debug) {
-								obj = *(void**)d.key_data;
-								if(!(arena_start <= obj && obj < arena_used))
-									runtime·throw("scanblock: inconsistent hashmap");
-							}
-							*ptrbufpos++ = (PtrTarget){*(void**)d.key_data, mapkey_ti};
-						}
-					}
-					if(!(mapval_kind & KindNoPointers) || d.indirectval) {
-						if(!d.indirectval)
-							*objbufpos++ = (Obj){d.val_data, mapval_size, mapval_ti};
-						else {
-							if(Debug) {
-								obj = *(void**)d.val_data;
-								if(!(arena_start <= obj && obj < arena_used))
-									runtime·throw("scanblock: inconsistent hashmap");
-							}
-							*ptrbufpos++ = (PtrTarget){*(void**)d.val_data, mapval_ti};
-						}
-					}
-				}
-			}
-			if(map_ret == nil)
-				goto next_block;
-			pc = map_ret;
-			continue;
-
 		case GC_REGION:
 			obj = (void*)(stack_top.b + pc[1]);
 			size = pc[2];
@@ -1077,7 +979,6 @@ scanblock(Workbuf *wbuf, Obj *wp, uintptr nobj, bool keepworking)
 			continue;
 
 		case GC_CHAN_PTR:
-			// Similar to GC_MAP_PTR
 			chan = *(Hchan**)(stack_top.b + pc[1]);
 			if(chan == nil) {
 				pc += 3;
diff --git a/src/pkg/runtime/mgc0.h b/src/pkg/runtime/mgc0.h
index d14fb37c2..f8abe6c9c 100644
--- a/src/pkg/runtime/mgc0.h
+++ b/src/pkg/runtime/mgc0.h
@@ -26,7 +26,6 @@ enum {
 	GC_ARRAY_START, // Start an array with a fixed length. Args: (off, len, elemsize)
 	GC_ARRAY_NEXT,  // The next element of an array. Args: none
 	GC_CALL,        // Call a subroutine. Args: (off, objgcrel)
-	GC_MAP_PTR,     // Go map. Args: (off, MapType*)
 	GC_CHAN_PTR,    // Go channel. Args: (off, ChanType*)
 	GC_STRING,      // Go string. Args: (off)
 	GC_EFACE,       // interface{}. Args: (off)
diff --git a/src/pkg/runtime/type.h b/src/pkg/runtime/type.h
index 075fffd5b..30936046c 100644
--- a/src/pkg/runtime/type.h
+++ b/src/pkg/runtime/type.h
@@ -70,6 +70,8 @@ struct MapType
 	Type;
 	Type *key;
 	Type *elem;
+	Type *bucket; // internal type representing a hash bucket
+	Type *hmap;   // internal type representing a Hmap
 };
 
 struct ChanType