runtime: rename map implementation and test files to use a common prefix

Rename all map implementation and test files to use "map"
as a file name prefix instead of "hashmap" for the implementation
and "map" for the test file names.

Change-Id: I7b317c1f7a660b95c6d1f1a185866f2839e69446
Reviewed-on: https://go-review.googlesource.com/90336
Run-TryBot: Martin Möhrmann <moehrmann@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

1 files changed, 1249 insertions, 0 deletions

diff --git a/src/runtime/map.go b/src/runtime/map.go
new file mode 100644
index 0000000000..eddb045622
--- /dev/null
+++ b/src/runtime/map.go
@@ -0,0 +1,1249 @@
+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package runtime
+
+// This file contains the implementation of Go's map type.
+//
+// A map is just a hash table. The data is arranged
+// into an array of buckets. Each bucket contains up to
+// 8 key/value pairs. The low-order bits of the hash are
+// used to select a bucket. Each bucket contains a few
+// high-order bits of each hash to distinguish the entries
+// within a single bucket.
+//
+// If more than 8 keys hash to a bucket, we chain on
+// extra buckets.
+//
+// When the hashtable grows, we allocate a new array
+// of buckets twice as big. Buckets are incrementally
+// copied from the old bucket array to the new bucket array.
+//
+// Map iterators walk through the array of buckets and
+// return the keys in walk order (bucket #, then overflow
+// chain order, then bucket index).  To maintain iteration
+// semantics, we never move keys within their bucket (if
+// we did, keys might be returned 0 or 2 times).  When
+// growing the table, iterators remain iterating through the
+// old table and must check the new table if the bucket
+// they are iterating through has been moved ("evacuated")
+// to the new table.
+
+// Picking loadFactor: too large and we have lots of overflow
+// buckets, too small and we waste a lot of space. I wrote
+// a simple program to check some stats for different loads:
+// (64-bit, 8 byte keys and values)
+//  loadFactor    %overflow  bytes/entry     hitprobe    missprobe
+//        4.00         2.13        20.77         3.00         4.00
+//        4.50         4.05        17.30         3.25         4.50
+//        5.00         6.85        14.77         3.50         5.00
+//        5.50        10.55        12.94         3.75         5.50
+//        6.00        15.27        11.67         4.00         6.00
+//        6.50        20.90        10.79         4.25         6.50
+//        7.00        27.14        10.15         4.50         7.00
+//        7.50        34.03         9.73         4.75         7.50
+//        8.00        41.10         9.40         5.00         8.00
+//
+// %overflow   = percentage of buckets which have an overflow bucket
+// bytes/entry = overhead bytes used per key/value pair
+// hitprobe    = # of entries to check when looking up a present key
+// missprobe   = # of entries to check when looking up an absent key
+//
+// Keep in mind this data is for maximally loaded tables, i.e. just
+// before the table grows. Typical tables will be somewhat less loaded.
+
+import (
+	"runtime/internal/atomic"
+	"runtime/internal/sys"
+	"unsafe"
+)
+
+const (
+	// Maximum number of key/value pairs a bucket can hold.
+	bucketCntBits = 3
+	bucketCnt     = 1 << bucketCntBits
+
+	// Maximum average load of a bucket that triggers growth is 6.5.
+	// Represent as loadFactorNum/loadFactDen, to allow integer math.
+	loadFactorNum = 13
+	loadFactorDen = 2
+
+	// Maximum key or value size to keep inline (instead of mallocing per element).
+	// Must fit in a uint8.
+	// Fast versions cannot handle big values - the cutoff size for
+	// fast versions in ../../cmd/internal/gc/walk.go must be at most this value.
+	maxKeySize   = 128
+	maxValueSize = 128
+
+	// data offset should be the size of the bmap struct, but needs to be
+	// aligned correctly. For amd64p32 this means 64-bit alignment
+	// even though pointers are 32 bit.
+	dataOffset = unsafe.Offsetof(struct {
+		b bmap
+		v int64
+	}{}.v)
+
+	// Possible tophash values. We reserve a few possibilities for special marks.
+	// Each bucket (including its overflow buckets, if any) will have either all or none of its
+	// entries in the evacuated* states (except during the evacuate() method, which only happens
+	// during map writes and thus no one else can observe the map during that time).
+	empty          = 0 // cell is empty
+	evacuatedEmpty = 1 // cell is empty, bucket is evacuated.
+	evacuatedX     = 2 // key/value is valid.  Entry has been evacuated to first half of larger table.
+	evacuatedY     = 3 // same as above, but evacuated to second half of larger table.
+	minTopHash     = 4 // minimum tophash for a normal filled cell.
+
+	// flags
+	iterator     = 1 // there may be an iterator using buckets
+	oldIterator  = 2 // there may be an iterator using oldbuckets
+	hashWriting  = 4 // a goroutine is writing to the map
+	sameSizeGrow = 8 // the current map growth is to a new map of the same size
+
+	// sentinel bucket ID for iterator checks
+	noCheck = 1<<(8*sys.PtrSize) - 1
+)
+
+// A header for a Go map.
+type hmap struct {
+	// Note: the format of the Hmap is encoded in ../../cmd/internal/gc/reflect.go and
+	// ../reflect/type.go. Don't change this structure without also changing that code!
+	count     int // # live cells == size of map.  Must be first (used by len() builtin)
+	flags     uint8
+	B         uint8  // log_2 of # of buckets (can hold up to loadFactor * 2^B items)
+	noverflow uint16 // approximate number of overflow buckets; see incrnoverflow for details
+	hash0     uint32 // hash seed
+
+	buckets    unsafe.Pointer // array of 2^B Buckets. may be nil if count==0.
+	oldbuckets unsafe.Pointer // previous bucket array of half the size, non-nil only when growing
+	nevacuate  uintptr        // progress counter for evacuation (buckets less than this have been evacuated)
+
+	extra *mapextra // optional fields
+}
+
+// mapextra holds fields that are not present on all maps.
+type mapextra struct {
+	// If both key and value do not contain pointers and are inline, then we mark bucket
+	// type as containing no pointers. This avoids scanning such maps.
+	// However, bmap.overflow is a pointer. In order to keep overflow buckets
+	// alive, we store pointers to all overflow buckets in hmap.overflow and h.map.oldoverflow.
+	// overflow and oldoverflow are only used if key and value do not contain pointers.
+	// overflow contains overflow buckets for hmap.buckets.
+	// oldoverflow contains overflow buckets for hmap.oldbuckets.
+	// The indirection allows to store a pointer to the slice in hiter.
+	overflow    *[]*bmap
+	oldoverflow *[]*bmap
+
+	// nextOverflow holds a pointer to a free overflow bucket.
+	nextOverflow *bmap
+}
+
+// A bucket for a Go map.
+type bmap struct {
+	// tophash generally contains the top byte of the hash value
+	// for each key in this bucket. If tophash[0] < minTopHash,
+	// tophash[0] is a bucket evacuation state instead.
+	tophash [bucketCnt]uint8
+	// Followed by bucketCnt keys and then bucketCnt values.
+	// NOTE: packing all the keys together and then all the values together makes the
+	// code a bit more complicated than alternating key/value/key/value/... but it allows
+	// us to eliminate padding which would be needed for, e.g., map[int64]int8.
+	// Followed by an overflow pointer.
+}
+
+// A hash iteration structure.
+// If you modify hiter, also change cmd/internal/gc/reflect.go to indicate
+// the layout of this structure.
+type hiter struct {
+	key         unsafe.Pointer // Must be in first position.  Write nil to indicate iteration end (see cmd/internal/gc/range.go).
+	value       unsafe.Pointer // Must be in second position (see cmd/internal/gc/range.go).
+	t           *maptype
+	h           *hmap
+	buckets     unsafe.Pointer // bucket ptr at hash_iter initialization time
+	bptr        *bmap          // current bucket
+	overflow    *[]*bmap       // keeps overflow buckets of hmap.buckets alive
+	oldoverflow *[]*bmap       // keeps overflow buckets of hmap.oldbuckets alive
+	startBucket uintptr        // bucket iteration started at
+	offset      uint8          // intra-bucket offset to start from during iteration (should be big enough to hold bucketCnt-1)
+	wrapped     bool           // already wrapped around from end of bucket array to beginning
+	B           uint8
+	i           uint8
+	bucket      uintptr
+	checkBucket uintptr
+}
+
+// bucketShift returns 1<<b, optimized for code generation.
+func bucketShift(b uint8) uintptr {
+	if sys.GoarchAmd64|sys.GoarchAmd64p32|sys.Goarch386 != 0 {
+		b &= sys.PtrSize*8 - 1 // help x86 archs remove shift overflow checks
+	}
+	return uintptr(1) << b
+}
+
+// bucketMask returns 1<<b - 1, optimized for code generation.
+func bucketMask(b uint8) uintptr {
+	return bucketShift(b) - 1
+}
+
+// tophash calculates the tophash value for hash.
+func tophash(hash uintptr) uint8 {
+	top := uint8(hash >> (sys.PtrSize*8 - 8))
+	if top < minTopHash {
+		top += minTopHash
+	}
+	return top
+}
+
+func evacuated(b *bmap) bool {
+	h := b.tophash[0]
+	return h > empty && h < minTopHash
+}
+
+func (b *bmap) overflow(t *maptype) *bmap {
+	return *(**bmap)(add(unsafe.Pointer(b), uintptr(t.bucketsize)-sys.PtrSize))
+}
+
+func (b *bmap) setoverflow(t *maptype, ovf *bmap) {
+	*(**bmap)(add(unsafe.Pointer(b), uintptr(t.bucketsize)-sys.PtrSize)) = ovf
+}
+
+func (b *bmap) keys() unsafe.Pointer {
+	return add(unsafe.Pointer(b), dataOffset)
+}
+
+// incrnoverflow increments h.noverflow.
+// noverflow counts the number of overflow buckets.
+// This is used to trigger same-size map growth.
+// See also tooManyOverflowBuckets.
+// To keep hmap small, noverflow is a uint16.
+// When there are few buckets, noverflow is an exact count.
+// When there are many buckets, noverflow is an approximate count.
+func (h *hmap) incrnoverflow() {
+	// We trigger same-size map growth if there are
+	// as many overflow buckets as buckets.
+	// We need to be able to count to 1<<h.B.
+	if h.B < 16 {
+		h.noverflow++
+		return
+	}
+	// Increment with probability 1/(1<<(h.B-15)).
+	// When we reach 1<<15 - 1, we will have approximately
+	// as many overflow buckets as buckets.
+	mask := uint32(1)<<(h.B-15) - 1
+	// Example: if h.B == 18, then mask == 7,
+	// and fastrand & 7 == 0 with probability 1/8.
+	if fastrand()&mask == 0 {
+		h.noverflow++
+	}
+}
+
+func (h *hmap) newoverflow(t *maptype, b *bmap) *bmap {
+	var ovf *bmap
+	if h.extra != nil && h.extra.nextOverflow != nil {
+		// We have preallocated overflow buckets available.
+		// See makeBucketArray for more details.
+		ovf = h.extra.nextOverflow
+		if ovf.overflow(t) == nil {
+			// We're not at the end of the preallocated overflow buckets. Bump the pointer.
+			h.extra.nextOverflow = (*bmap)(add(unsafe.Pointer(ovf), uintptr(t.bucketsize)))
+		} else {
+			// This is the last preallocated overflow bucket.
+			// Reset the overflow pointer on this bucket,
+			// which was set to a non-nil sentinel value.
+			ovf.setoverflow(t, nil)
+			h.extra.nextOverflow = nil
+		}
+	} else {
+		ovf = (*bmap)(newobject(t.bucket))
+	}
+	h.incrnoverflow()
+	if t.bucket.kind&kindNoPointers != 0 {
+		h.createOverflow()
+		*h.extra.overflow = append(*h.extra.overflow, ovf)
+	}
+	b.setoverflow(t, ovf)
+	return ovf
+}
+
+func (h *hmap) createOverflow() {
+	if h.extra == nil {
+		h.extra = new(mapextra)
+	}
+	if h.extra.overflow == nil {
+		h.extra.overflow = new([]*bmap)
+	}
+}
+
+func makemap64(t *maptype, hint int64, h *hmap) *hmap {
+	if int64(int(hint)) != hint {
+		hint = 0
+	}
+	return makemap(t, int(hint), h)
+}
+
+// makehmap_small implements Go map creation for make(map[k]v) and
+// make(map[k]v, hint) when hint is known to be at most bucketCnt
+// at compile time and the map needs to be allocated on the heap.
+func makemap_small() *hmap {
+	h := new(hmap)
+	h.hash0 = fastrand()
+	return h
+}
+
+// makemap implements Go map creation for make(map[k]v, hint).
+// If the compiler has determined that the map or the first bucket
+// can be created on the stack, h and/or bucket may be non-nil.
+// If h != nil, the map can be created directly in h.
+// If h.buckets != nil, bucket pointed to can be used as the first bucket.
+func makemap(t *maptype, hint int, h *hmap) *hmap {
+	// The size of hmap should be 48 bytes on 64 bit
+	// and 28 bytes on 32 bit platforms.
+	if sz := unsafe.Sizeof(hmap{}); sz != 8+5*sys.PtrSize {
+		println("runtime: sizeof(hmap) =", sz, ", t.hmap.size =", t.hmap.size)
+		throw("bad hmap size")
+	}
+
+	if hint < 0 || hint > int(maxSliceCap(t.bucket.size)) {
+		hint = 0
+	}
+
+	// initialize Hmap
+	if h == nil {
+		h = new(hmap)
+	}
+	h.hash0 = fastrand()
+
+	// find size parameter which will hold the requested # of elements
+	B := uint8(0)
+	for overLoadFactor(hint, B) {
+		B++
+	}
+	h.B = B
+
+	// allocate initial hash table
+	// if B == 0, the buckets field is allocated lazily later (in mapassign)
+	// If hint is large zeroing this memory could take a while.
+	if h.B != 0 {
+		var nextOverflow *bmap
+		h.buckets, nextOverflow = makeBucketArray(t, h.B)
+		if nextOverflow != nil {
+			h.extra = new(mapextra)
+			h.extra.nextOverflow = nextOverflow
+		}
+	}
+
+	return h
+}
+
+// mapaccess1 returns a pointer to h[key].  Never returns nil, instead
+// it will return a reference to the zero object for the value type if
+// the key is not in the map.
+// NOTE: The returned pointer may keep the whole map live, so don't
+// hold onto it for very long.
+func mapaccess1(t *maptype, h *hmap, key unsafe.Pointer) unsafe.Pointer {
+	if raceenabled && h != nil {
+		callerpc := getcallerpc()
+		pc := funcPC(mapaccess1)
+		racereadpc(unsafe.Pointer(h), callerpc, pc)
+		raceReadObjectPC(t.key, key, callerpc, pc)
+	}
+	if msanenabled && h != nil {
+		msanread(key, t.key.size)
+	}
+	if h == nil || h.count == 0 {
+		return unsafe.Pointer(&zeroVal[0])
+	}
+	if h.flags&hashWriting != 0 {
+		throw("concurrent map read and map write")
+	}
+	alg := t.key.alg
+	hash := alg.hash(key, uintptr(h.hash0))
+	m := bucketMask(h.B)
+	b := (*bmap)(add(h.buckets, (hash&m)*uintptr(t.bucketsize)))
+	if c := h.oldbuckets; c != nil {
+		if !h.sameSizeGrow() {
+			// There used to be half as many buckets; mask down one more power of two.
+			m >>= 1
+		}
+		oldb := (*bmap)(add(c, (hash&m)*uintptr(t.bucketsize)))
+		if !evacuated(oldb) {
+			b = oldb
+		}
+	}
+	top := tophash(hash)
+	for ; b != nil; b = b.overflow(t) {
+		for i := uintptr(0); i < bucketCnt; i++ {
+			if b.tophash[i] != top {
+				continue
+			}
+			k := add(unsafe.Pointer(b), dataOffset+i*uintptr(t.keysize))
+			if t.indirectkey {
+				k = *((*unsafe.Pointer)(k))
+			}
+			if alg.equal(key, k) {
+				v := add(unsafe.Pointer(b), dataOffset+bucketCnt*uintptr(t.keysize)+i*uintptr(t.valuesize))
+				if t.indirectvalue {
+					v = *((*unsafe.Pointer)(v))
+				}
+				return v
+			}
+		}
+	}
+	return unsafe.Pointer(&zeroVal[0])
+}
+
+func mapaccess2(t *maptype, h *hmap, key unsafe.Pointer) (unsafe.Pointer, bool) {
+	if raceenabled && h != nil {
+		callerpc := getcallerpc()
+		pc := funcPC(mapaccess2)
+		racereadpc(unsafe.Pointer(h), callerpc, pc)
+		raceReadObjectPC(t.key, key, callerpc, pc)
+	}
+	if msanenabled && h != nil {
+		msanread(key, t.key.size)
+	}
+	if h == nil || h.count == 0 {
+		return unsafe.Pointer(&zeroVal[0]), false
+	}
+	if h.flags&hashWriting != 0 {
+		throw("concurrent map read and map write")
+	}
+	alg := t.key.alg
+	hash := alg.hash(key, uintptr(h.hash0))
+	m := bucketMask(h.B)
+	b := (*bmap)(unsafe.Pointer(uintptr(h.buckets) + (hash&m)*uintptr(t.bucketsize)))
+	if c := h.oldbuckets; c != nil {
+		if !h.sameSizeGrow() {
+			// There used to be half as many buckets; mask down one more power of two.
+			m >>= 1
+		}
+		oldb := (*bmap)(unsafe.Pointer(uintptr(c) + (hash&m)*uintptr(t.bucketsize)))
+		if !evacuated(oldb) {
+			b = oldb
+		}
+	}
+	top := tophash(hash)
+	for ; b != nil; b = b.overflow(t) {
+		for i := uintptr(0); i < bucketCnt; i++ {
+			if b.tophash[i] != top {
+				continue
+			}
+			k := add(unsafe.Pointer(b), dataOffset+i*uintptr(t.keysize))
+			if t.indirectkey {
+				k = *((*unsafe.Pointer)(k))
+			}
+			if alg.equal(key, k) {
+				v := add(unsafe.Pointer(b), dataOffset+bucketCnt*uintptr(t.keysize)+i*uintptr(t.valuesize))
+				if t.indirectvalue {
+					v = *((*unsafe.Pointer)(v))
+				}
+				return v, true
+			}
+		}
+	}
+	return unsafe.Pointer(&zeroVal[0]), false
+}
+
+// returns both key and value. Used by map iterator
+func mapaccessK(t *maptype, h *hmap, key unsafe.Pointer) (unsafe.Pointer, unsafe.Pointer) {
+	if h == nil || h.count == 0 {
+		return nil, nil
+	}
+	alg := t.key.alg
+	hash := alg.hash(key, uintptr(h.hash0))
+	m := bucketMask(h.B)
+	b := (*bmap)(unsafe.Pointer(uintptr(h.buckets) + (hash&m)*uintptr(t.bucketsize)))
+	if c := h.oldbuckets; c != nil {
+		if !h.sameSizeGrow() {
+			// There used to be half as many buckets; mask down one more power of two.
+			m >>= 1
+		}
+		oldb := (*bmap)(unsafe.Pointer(uintptr(c) + (hash&m)*uintptr(t.bucketsize)))
+		if !evacuated(oldb) {
+			b = oldb
+		}
+	}
+	top := tophash(hash)
+	for ; b != nil; b = b.overflow(t) {
+		for i := uintptr(0); i < bucketCnt; i++ {
+			if b.tophash[i] != top {
+				continue
+			}
+			k := add(unsafe.Pointer(b), dataOffset+i*uintptr(t.keysize))
+			if t.indirectkey {
+				k = *((*unsafe.Pointer)(k))
+			}
+			if alg.equal(key, k) {
+				v := add(unsafe.Pointer(b), dataOffset+bucketCnt*uintptr(t.keysize)+i*uintptr(t.valuesize))
+				if t.indirectvalue {
+					v = *((*unsafe.Pointer)(v))
+				}
+				return k, v
+			}
+		}
+	}
+	return nil, nil
+}
+
+func mapaccess1_fat(t *maptype, h *hmap, key, zero unsafe.Pointer) unsafe.Pointer {
+	v := mapaccess1(t, h, key)
+	if v == unsafe.Pointer(&zeroVal[0]) {
+		return zero
+	}
+	return v
+}
+
+func mapaccess2_fat(t *maptype, h *hmap, key, zero unsafe.Pointer) (unsafe.Pointer, bool) {
+	v := mapaccess1(t, h, key)
+	if v == unsafe.Pointer(&zeroVal[0]) {
+		return zero, false
+	}
+	return v, true
+}
+
+// Like mapaccess, but allocates a slot for the key if it is not present in the map.
+func mapassign(t *maptype, h *hmap, key unsafe.Pointer) unsafe.Pointer {
+	if h == nil {
+		panic(plainError("assignment to entry in nil map"))
+	}
+	if raceenabled {
+		callerpc := getcallerpc()
+		pc := funcPC(mapassign)
+		racewritepc(unsafe.Pointer(h), callerpc, pc)
+		raceReadObjectPC(t.key, key, callerpc, pc)
+	}
+	if msanenabled {
+		msanread(key, t.key.size)
+	}
+	if h.flags&hashWriting != 0 {
+		throw("concurrent map writes")
+	}
+	alg := t.key.alg
+	hash := alg.hash(key, uintptr(h.hash0))
+
+	// Set hashWriting after calling alg.hash, since alg.hash may panic,
+	// in which case we have not actually done a write.
+	h.flags |= hashWriting
+
+	if h.buckets == nil {
+		h.buckets = newobject(t.bucket) // newarray(t.bucket, 1)
+	}
+
+again:
+	bucket := hash & bucketMask(h.B)
+	if h.growing() {
+		growWork(t, h, bucket)
+	}
+	b := (*bmap)(unsafe.Pointer(uintptr(h.buckets) + bucket*uintptr(t.bucketsize)))
+	top := tophash(hash)
+
+	var inserti *uint8
+	var insertk unsafe.Pointer
+	var val unsafe.Pointer
+	for {
+		for i := uintptr(0); i < bucketCnt; i++ {
+			if b.tophash[i] != top {
+				if b.tophash[i] == empty && inserti == nil {
+					inserti = &b.tophash[i]
+					insertk = add(unsafe.Pointer(b), dataOffset+i*uintptr(t.keysize))
+					val = add(unsafe.Pointer(b), dataOffset+bucketCnt*uintptr(t.keysize)+i*uintptr(t.valuesize))
+				}
+				continue
+			}
+			k := add(unsafe.Pointer(b), dataOffset+i*uintptr(t.keysize))
+			if t.indirectkey {
+				k = *((*unsafe.Pointer)(k))
+			}
+			if !alg.equal(key, k) {
+				continue
+			}
+			// already have a mapping for key. Update it.
+			if t.needkeyupdate {
+				typedmemmove(t.key, k, key)
+			}
+			val = add(unsafe.Pointer(b), dataOffset+bucketCnt*uintptr(t.keysize)+i*uintptr(t.valuesize))
+			goto done
+		}
+		ovf := b.overflow(t)
+		if ovf == nil {
+			break
+		}
+		b = ovf
+	}
+
+	// Did not find mapping for key. Allocate new cell & add entry.
+
+	// If we hit the max load factor or we have too many overflow buckets,
+	// and we're not already in the middle of growing, start growing.
+	if !h.growing() && (overLoadFactor(h.count+1, h.B) || tooManyOverflowBuckets(h.noverflow, h.B)) {
+		hashGrow(t, h)
+		goto again // Growing the table invalidates everything, so try again
+	}
+
+	if inserti == nil {
+		// all current buckets are full, allocate a new one.
+		newb := h.newoverflow(t, b)
+		inserti = &newb.tophash[0]
+		insertk = add(unsafe.Pointer(newb), dataOffset)
+		val = add(insertk, bucketCnt*uintptr(t.keysize))
+	}
+
+	// store new key/value at insert position
+	if t.indirectkey {
+		kmem := newobject(t.key)
+		*(*unsafe.Pointer)(insertk) = kmem
+		insertk = kmem
+	}
+	if t.indirectvalue {
+		vmem := newobject(t.elem)
+		*(*unsafe.Pointer)(val) = vmem
+	}
+	typedmemmove(t.key, insertk, key)
+	*inserti = top
+	h.count++
+
+done:
+	if h.flags&hashWriting == 0 {
+		throw("concurrent map writes")
+	}
+	h.flags &^= hashWriting
+	if t.indirectvalue {
+		val = *((*unsafe.Pointer)(val))
+	}
+	return val
+}
+
+func mapdelete(t *maptype, h *hmap, key unsafe.Pointer) {
+	if raceenabled && h != nil {
+		callerpc := getcallerpc()
+		pc := funcPC(mapdelete)
+		racewritepc(unsafe.Pointer(h), callerpc, pc)
+		raceReadObjectPC(t.key, key, callerpc, pc)
+	}
+	if msanenabled && h != nil {
+		msanread(key, t.key.size)
+	}
+	if h == nil || h.count == 0 {
+		return
+	}
+	if h.flags&hashWriting != 0 {
+		throw("concurrent map writes")
+	}
+
+	alg := t.key.alg
+	hash := alg.hash(key, uintptr(h.hash0))
+
+	// Set hashWriting after calling alg.hash, since alg.hash may panic,
+	// in which case we have not actually done a write (delete).
+	h.flags |= hashWriting
+
+	bucket := hash & bucketMask(h.B)
+	if h.growing() {
+		growWork(t, h, bucket)
+	}
+	b := (*bmap)(add(h.buckets, bucket*uintptr(t.bucketsize)))
+	top := tophash(hash)
+search:
+	for ; b != nil; b = b.overflow(t) {
+		for i := uintptr(0); i < bucketCnt; i++ {
+			if b.tophash[i] != top {
+				continue
+			}
+			k := add(unsafe.Pointer(b), dataOffset+i*uintptr(t.keysize))
+			k2 := k
+			if t.indirectkey {
+				k2 = *((*unsafe.Pointer)(k2))
+			}
+			if !alg.equal(key, k2) {
+				continue
+			}
+			// Only clear key if there are pointers in it.
+			if t.indirectkey {
+				*(*unsafe.Pointer)(k) = nil
+			} else if t.key.kind&kindNoPointers == 0 {
+				memclrHasPointers(k, t.key.size)
+			}
+			// Only clear value if there are pointers in it.
+			if t.indirectvalue || t.elem.kind&kindNoPointers == 0 {
+				v := add(unsafe.Pointer(b), dataOffset+bucketCnt*uintptr(t.keysize)+i*uintptr(t.valuesize))
+				if t.indirectvalue {
+					*(*unsafe.Pointer)(v) = nil
+				} else {
+					memclrHasPointers(v, t.elem.size)
+				}
+			}
+			b.tophash[i] = empty
+			h.count--
+			break search
+		}
+	}
+
+	if h.flags&hashWriting == 0 {
+		throw("concurrent map writes")
+	}
+	h.flags &^= hashWriting
+}
+
+// mapiterinit initializes the hiter struct used for ranging over maps.
+// The hiter struct pointed to by 'it' is allocated on the stack
+// by the compilers order pass or on the heap by reflect_mapiterinit.
+// Both need to have zeroed hiter since the struct contains pointers.
+func mapiterinit(t *maptype, h *hmap, it *hiter) {
+	if raceenabled && h != nil {
+		callerpc := getcallerpc()
+		racereadpc(unsafe.Pointer(h), callerpc, funcPC(mapiterinit))
+	}
+
+	if h == nil || h.count == 0 {
+		return
+	}
+
+	if unsafe.Sizeof(hiter{})/sys.PtrSize != 12 {
+		throw("hash_iter size incorrect") // see ../../cmd/internal/gc/reflect.go
+	}
+	it.t = t
+	it.h = h
+
+	// grab snapshot of bucket state
+	it.B = h.B
+	it.buckets = h.buckets
+	if t.bucket.kind&kindNoPointers != 0 {
+		// Allocate the current slice and remember pointers to both current and old.
+		// This preserves all relevant overflow buckets alive even if
+		// the table grows and/or overflow buckets are added to the table
+		// while we are iterating.
+		h.createOverflow()
+		it.overflow = h.extra.overflow
+		it.oldoverflow = h.extra.oldoverflow
+	}
+
+	// decide where to start
+	r := uintptr(fastrand())
+	if h.B > 31-bucketCntBits {
+		r += uintptr(fastrand()) << 31
+	}
+	it.startBucket = r & bucketMask(h.B)
+	it.offset = uint8(r >> h.B & (bucketCnt - 1))
+
+	// iterator state
+	it.bucket = it.startBucket
+
+	// Remember we have an iterator.
+	// Can run concurrently with another mapiterinit().
+	if old := h.flags; old&(iterator|oldIterator) != iterator|oldIterator {
+		atomic.Or8(&h.flags, iterator|oldIterator)
+	}
+
+	mapiternext(it)
+}
+
+func mapiternext(it *hiter) {
+	h := it.h
+	if raceenabled {
+		callerpc := getcallerpc()
+		racereadpc(unsafe.Pointer(h), callerpc, funcPC(mapiternext))
+	}
+	if h.flags&hashWriting != 0 {
+		throw("concurrent map iteration and map write")
+	}
+	t := it.t
+	bucket := it.bucket
+	b := it.bptr
+	i := it.i
+	checkBucket := it.checkBucket
+	alg := t.key.alg
+
+next:
+	if b == nil {
+		if bucket == it.startBucket && it.wrapped {
+			// end of iteration
+			it.key = nil
+			it.value = nil
+			return
+		}
+		if h.growing() && it.B == h.B {
+			// Iterator was started in the middle of a grow, and the grow isn't done yet.
+			// If the bucket we're looking at hasn't been filled in yet (i.e. the old
+			// bucket hasn't been evacuated) then we need to iterate through the old
+			// bucket and only return the ones that will be migrated to this bucket.
+			oldbucket := bucket & it.h.oldbucketmask()
+			b = (*bmap)(add(h.oldbuckets, oldbucket*uintptr(t.bucketsize)))
+			if !evacuated(b) {
+				checkBucket = bucket
+			} else {
+				b = (*bmap)(add(it.buckets, bucket*uintptr(t.bucketsize)))
+				checkBucket = noCheck
+			}
+		} else {
+			b = (*bmap)(add(it.buckets, bucket*uintptr(t.bucketsize)))
+			checkBucket = noCheck
+		}
+		bucket++
+		if bucket == bucketShift(it.B) {
+			bucket = 0
+			it.wrapped = true
+		}
+		i = 0
+	}
+	for ; i < bucketCnt; i++ {
+		offi := (i + it.offset) & (bucketCnt - 1)
+		if b.tophash[offi] == empty || b.tophash[offi] == evacuatedEmpty {
+			continue
+		}
+		k := add(unsafe.Pointer(b), dataOffset+uintptr(offi)*uintptr(t.keysize))
+		if t.indirectkey {
+			k = *((*unsafe.Pointer)(k))
+		}
+		v := add(unsafe.Pointer(b), dataOffset+bucketCnt*uintptr(t.keysize)+uintptr(offi)*uintptr(t.valuesize))
+		if checkBucket != noCheck && !h.sameSizeGrow() {
+			// Special case: iterator was started during a grow to a larger size
+			// and the grow is not done yet. We're working on a bucket whose
+			// oldbucket has not been evacuated yet. Or at least, it wasn't
+			// evacuated when we started the bucket. So we're iterating
+			// through the oldbucket, skipping any keys that will go
+			// to the other new bucket (each oldbucket expands to two
+			// buckets during a grow).
+			if t.reflexivekey || alg.equal(k, k) {
+				// If the item in the oldbucket is not destined for
+				// the current new bucket in the iteration, skip it.
+				hash := alg.hash(k, uintptr(h.hash0))
+				if hash&bucketMask(it.B) != checkBucket {
+					continue
+				}
+			} else {
+				// Hash isn't repeatable if k != k (NaNs).  We need a
+				// repeatable and randomish choice of which direction
+				// to send NaNs during evacuation. We'll use the low
+				// bit of tophash to decide which way NaNs go.
+				// NOTE: this case is why we need two evacuate tophash
+				// values, evacuatedX and evacuatedY, that differ in
+				// their low bit.
+				if checkBucket>>(it.B-1) != uintptr(b.tophash[offi]&1) {
+					continue
+				}
+			}
+		}
+		if (b.tophash[offi] != evacuatedX && b.tophash[offi] != evacuatedY) ||
+			!(t.reflexivekey || alg.equal(k, k)) {
+			// This is the golden data, we can return it.
+			// OR
+			// key!=key, so the entry can't be deleted or updated, so we can just return it.
+			// That's lucky for us because when key!=key we can't look it up successfully.
+			it.key = k
+			if t.indirectvalue {
+				v = *((*unsafe.Pointer)(v))
+			}
+			it.value = v
+		} else {
+			// The hash table has grown since the iterator was started.
+			// The golden data for this key is now somewhere else.
+			// Check the current hash table for the data.
+			// This code handles the case where the key
+			// has been deleted, updated, or deleted and reinserted.
+			// NOTE: we need to regrab the key as it has potentially been
+			// updated to an equal() but not identical key (e.g. +0.0 vs -0.0).
+			rk, rv := mapaccessK(t, h, k)
+			if rk == nil {
+				continue // key has been deleted
+			}
+			it.key = rk
+			it.value = rv
+		}
+		it.bucket = bucket
+		if it.bptr != b { // avoid unnecessary write barrier; see issue 14921
+			it.bptr = b
+		}
+		it.i = i + 1
+		it.checkBucket = checkBucket
+		return
+	}
+	b = b.overflow(t)
+	i = 0
+	goto next
+}
+
+func makeBucketArray(t *maptype, b uint8) (buckets unsafe.Pointer, nextOverflow *bmap) {
+	base := bucketShift(b)
+	nbuckets := base
+	// For small b, overflow buckets are unlikely.
+	// Avoid the overhead of the calculation.
+	if b >= 4 {
+		// Add on the estimated number of overflow buckets
+		// required to insert the median number of elements
+		// used with this value of b.
+		nbuckets += bucketShift(b - 4)
+		sz := t.bucket.size * nbuckets
+		up := roundupsize(sz)
+		if up != sz {
+			nbuckets = up / t.bucket.size
+		}
+	}
+	buckets = newarray(t.bucket, int(nbuckets))
+	if base != nbuckets {
+		// We preallocated some overflow buckets.
+		// To keep the overhead of tracking these overflow buckets to a minimum,
+		// we use the convention that if a preallocated overflow bucket's overflow
+		// pointer is nil, then there are more available by bumping the pointer.
+		// We need a safe non-nil pointer for the last overflow bucket; just use buckets.
+		nextOverflow = (*bmap)(add(buckets, base*uintptr(t.bucketsize)))
+		last := (*bmap)(add(buckets, (nbuckets-1)*uintptr(t.bucketsize)))
+		last.setoverflow(t, (*bmap)(buckets))
+	}
+	return buckets, nextOverflow
+}
+
+func hashGrow(t *maptype, h *hmap) {
+	// If we've hit the load factor, get bigger.
+	// Otherwise, there are too many overflow buckets,
+	// so keep the same number of buckets and "grow" laterally.
+	bigger := uint8(1)
+	if !overLoadFactor(h.count+1, h.B) {
+		bigger = 0
+		h.flags |= sameSizeGrow
+	}
+	oldbuckets := h.buckets
+	newbuckets, nextOverflow := makeBucketArray(t, h.B+bigger)
+
+	flags := h.flags &^ (iterator | oldIterator)
+	if h.flags&iterator != 0 {
+		flags |= oldIterator
+	}
+	// commit the grow (atomic wrt gc)
+	h.B += bigger
+	h.flags = flags
+	h.oldbuckets = oldbuckets
+	h.buckets = newbuckets
+	h.nevacuate = 0
+	h.noverflow = 0
+
+	if h.extra != nil && h.extra.overflow != nil {
+		// Promote current overflow buckets to the old generation.
+		if h.extra.oldoverflow != nil {
+			throw("oldoverflow is not nil")
+		}
+		h.extra.oldoverflow = h.extra.overflow
+		h.extra.overflow = nil
+	}
+	if nextOverflow != nil {
+		if h.extra == nil {
+			h.extra = new(mapextra)
+		}
+		h.extra.nextOverflow = nextOverflow
+	}
+
+	// the actual copying of the hash table data is done incrementally
+	// by growWork() and evacuate().
+}
+
+// overLoadFactor reports whether count items placed in 1<<B buckets is over loadFactor.
+func overLoadFactor(count int, B uint8) bool {
+	return count > bucketCnt && uintptr(count) > loadFactorNum*(bucketShift(B)/loadFactorDen)
+}
+
+// tooManyOverflowBuckets reports whether noverflow buckets is too many for a map with 1<<B buckets.
+// Note that most of these overflow buckets must be in sparse use;
+// if use was dense, then we'd have already triggered regular map growth.
+func tooManyOverflowBuckets(noverflow uint16, B uint8) bool {
+	// If the threshold is too low, we do extraneous work.
+	// If the threshold is too high, maps that grow and shrink can hold on to lots of unused memory.
+	// "too many" means (approximately) as many overflow buckets as regular buckets.
+	// See incrnoverflow for more details.
+	if B > 15 {
+		B = 15
+	}
+	// The compiler doesn't see here that B < 16; mask B to generate shorter shift code.
+	return noverflow >= uint16(1)<<(B&15)
+}
+
+// growing reports whether h is growing. The growth may be to the same size or bigger.
+func (h *hmap) growing() bool {
+	return h.oldbuckets != nil
+}
+
+// sameSizeGrow reports whether the current growth is to a map of the same size.
+func (h *hmap) sameSizeGrow() bool {
+	return h.flags&sameSizeGrow != 0
+}
+
+// noldbuckets calculates the number of buckets prior to the current map growth.
+func (h *hmap) noldbuckets() uintptr {
+	oldB := h.B
+	if !h.sameSizeGrow() {
+		oldB--
+	}
+	return bucketShift(oldB)
+}
+
+// oldbucketmask provides a mask that can be applied to calculate n % noldbuckets().
+func (h *hmap) oldbucketmask() uintptr {
+	return h.noldbuckets() - 1
+}
+
+func growWork(t *maptype, h *hmap, bucket uintptr) {
+	// make sure we evacuate the oldbucket corresponding
+	// to the bucket we're about to use
+	evacuate(t, h, bucket&h.oldbucketmask())
+
+	// evacuate one more oldbucket to make progress on growing
+	if h.growing() {
+		evacuate(t, h, h.nevacuate)
+	}
+}
+
+func bucketEvacuated(t *maptype, h *hmap, bucket uintptr) bool {
+	b := (*bmap)(add(h.oldbuckets, bucket*uintptr(t.bucketsize)))
+	return evacuated(b)
+}
+
+// evacDst is an evacuation destination.
+type evacDst struct {
+	b *bmap          // current destination bucket
+	i int            // key/val index into b
+	k unsafe.Pointer // pointer to current key storage
+	v unsafe.Pointer // pointer to current value storage
+}
+
+func evacuate(t *maptype, h *hmap, oldbucket uintptr) {
+	b := (*bmap)(add(h.oldbuckets, oldbucket*uintptr(t.bucketsize)))
+	newbit := h.noldbuckets()
+	if !evacuated(b) {
+		// TODO: reuse overflow buckets instead of using new ones, if there
+		// is no iterator using the old buckets.  (If !oldIterator.)
+
+		// xy contains the x and y (low and high) evacuation destinations.
+		var xy [2]evacDst
+		x := &xy[0]
+		x.b = (*bmap)(add(h.buckets, oldbucket*uintptr(t.bucketsize)))
+		x.k = add(unsafe.Pointer(x.b), dataOffset)
+		x.v = add(x.k, bucketCnt*uintptr(t.keysize))
+
+		if !h.sameSizeGrow() {
+			// Only calculate y pointers if we're growing bigger.
+			// Otherwise GC can see bad pointers.
+			y := &xy[1]
+			y.b = (*bmap)(add(h.buckets, (oldbucket+newbit)*uintptr(t.bucketsize)))
+			y.k = add(unsafe.Pointer(y.b), dataOffset)
+			y.v = add(y.k, bucketCnt*uintptr(t.keysize))
+		}
+
+		for ; b != nil; b = b.overflow(t) {
+			k := add(unsafe.Pointer(b), dataOffset)
+			v := add(k, bucketCnt*uintptr(t.keysize))
+			for i := 0; i < bucketCnt; i, k, v = i+1, add(k, uintptr(t.keysize)), add(v, uintptr(t.valuesize)) {
+				top := b.tophash[i]
+				if top == empty {
+					b.tophash[i] = evacuatedEmpty
+					continue
+				}
+				if top < minTopHash {
+					throw("bad map state")
+				}
+				k2 := k
+				if t.indirectkey {
+					k2 = *((*unsafe.Pointer)(k2))
+				}
+				var useY uint8
+				if !h.sameSizeGrow() {
+					// Compute hash to make our evacuation decision (whether we need
+					// to send this key/value to bucket x or bucket y).
+					hash := t.key.alg.hash(k2, uintptr(h.hash0))
+					if h.flags&iterator != 0 && !t.reflexivekey && !t.key.alg.equal(k2, k2) {
+						// If key != key (NaNs), then the hash could be (and probably
+						// will be) entirely different from the old hash. Moreover,
+						// it isn't reproducible. Reproducibility is required in the
+						// presence of iterators, as our evacuation decision must
+						// match whatever decision the iterator made.
+						// Fortunately, we have the freedom to send these keys either
+						// way. Also, tophash is meaningless for these kinds of keys.
+						// We let the low bit of tophash drive the evacuation decision.
+						// We recompute a new random tophash for the next level so
+						// these keys will get evenly distributed across all buckets
+						// after multiple grows.
+						useY = top & 1
+						top = tophash(hash)
+					} else {
+						if hash&newbit != 0 {
+							useY = 1
+						}
+					}
+				}
+
+				if evacuatedX+1 != evacuatedY {
+					throw("bad evacuatedN")
+				}
+
+				b.tophash[i] = evacuatedX + useY // evacuatedX + 1 == evacuatedY
+				dst := &xy[useY]                 // evacuation destination
+
+				if dst.i == bucketCnt {
+					dst.b = h.newoverflow(t, dst.b)
+					dst.i = 0
+					dst.k = add(unsafe.Pointer(dst.b), dataOffset)
+					dst.v = add(dst.k, bucketCnt*uintptr(t.keysize))
+				}
+				dst.b.tophash[dst.i&(bucketCnt-1)] = top // mask dst.i as an optimization, to avoid a bounds check
+				if t.indirectkey {
+					*(*unsafe.Pointer)(dst.k) = k2 // copy pointer
+				} else {
+					typedmemmove(t.key, dst.k, k) // copy value
+				}
+				if t.indirectvalue {
+					*(*unsafe.Pointer)(dst.v) = *(*unsafe.Pointer)(v)
+				} else {
+					typedmemmove(t.elem, dst.v, v)
+				}
+				dst.i++
+				// These updates might push these pointers past the end of the
+				// key or value arrays.  That's ok, as we have the overflow pointer
+				// at the end of the bucket to protect against pointing past the
+				// end of the bucket.
+				dst.k = add(dst.k, uintptr(t.keysize))
+				dst.v = add(dst.v, uintptr(t.valuesize))
+			}
+		}
+		// Unlink the overflow buckets & clear key/value to help GC.
+		if h.flags&oldIterator == 0 && t.bucket.kind&kindNoPointers == 0 {
+			b := add(h.oldbuckets, oldbucket*uintptr(t.bucketsize))
+			// Preserve b.tophash because the evacuation
+			// state is maintained there.
+			ptr := add(b, dataOffset)
+			n := uintptr(t.bucketsize) - dataOffset
+			memclrHasPointers(ptr, n)
+		}
+	}
+
+	if oldbucket == h.nevacuate {
+		advanceEvacuationMark(h, t, newbit)
+	}
+}
+
+func advanceEvacuationMark(h *hmap, t *maptype, newbit uintptr) {
+	h.nevacuate++
+	// Experiments suggest that 1024 is overkill by at least an order of magnitude.
+	// Put it in there as a safeguard anyway, to ensure O(1) behavior.
+	stop := h.nevacuate + 1024
+	if stop > newbit {
+		stop = newbit
+	}
+	for h.nevacuate != stop && bucketEvacuated(t, h, h.nevacuate) {
+		h.nevacuate++
+	}
+	if h.nevacuate == newbit { // newbit == # of oldbuckets
+		// Growing is all done. Free old main bucket array.
+		h.oldbuckets = nil
+		// Can discard old overflow buckets as well.
+		// If they are still referenced by an iterator,
+		// then the iterator holds a pointers to the slice.
+		if h.extra != nil {
+			h.extra.oldoverflow = nil
+		}
+		h.flags &^= sameSizeGrow
+	}
+}
+
+func ismapkey(t *_type) bool {
+	return t.alg.hash != nil
+}
+
+// Reflect stubs. Called from ../reflect/asm_*.s
+
+//go:linkname reflect_makemap reflect.makemap
+func reflect_makemap(t *maptype, cap int) *hmap {
+	// Check invariants and reflects math.
+	if sz := unsafe.Sizeof(hmap{}); sz != t.hmap.size {
+		println("runtime: sizeof(hmap) =", sz, ", t.hmap.size =", t.hmap.size)
+		throw("bad hmap size")
+	}
+	if !ismapkey(t.key) {
+		throw("runtime.reflect_makemap: unsupported map key type")
+	}
+	if t.key.size > maxKeySize && (!t.indirectkey || t.keysize != uint8(sys.PtrSize)) ||
+		t.key.size <= maxKeySize && (t.indirectkey || t.keysize != uint8(t.key.size)) {
+		throw("key size wrong")
+	}
+	if t.elem.size > maxValueSize && (!t.indirectvalue || t.valuesize != uint8(sys.PtrSize)) ||
+		t.elem.size <= maxValueSize && (t.indirectvalue || t.valuesize != uint8(t.elem.size)) {
+		throw("value size wrong")
+	}
+	if t.key.align > bucketCnt {
+		throw("key align too big")
+	}
+	if t.elem.align > bucketCnt {
+		throw("value align too big")
+	}
+	if t.key.size%uintptr(t.key.align) != 0 {
+		throw("key size not a multiple of key align")
+	}
+	if t.elem.size%uintptr(t.elem.align) != 0 {
+		throw("value size not a multiple of value align")
+	}
+	if bucketCnt < 8 {
+		throw("bucketsize too small for proper alignment")
+	}
+	if dataOffset%uintptr(t.key.align) != 0 {
+		throw("need padding in bucket (key)")
+	}
+	if dataOffset%uintptr(t.elem.align) != 0 {
+		throw("need padding in bucket (value)")
+	}
+
+	return makemap(t, cap, nil)
+}
+
+//go:linkname reflect_mapaccess reflect.mapaccess
+func reflect_mapaccess(t *maptype, h *hmap, key unsafe.Pointer) unsafe.Pointer {
+	val, ok := mapaccess2(t, h, key)
+	if !ok {
+		// reflect wants nil for a missing element
+		val = nil
+	}
+	return val
+}
+
+//go:linkname reflect_mapassign reflect.mapassign
+func reflect_mapassign(t *maptype, h *hmap, key unsafe.Pointer, val unsafe.Pointer) {
+	p := mapassign(t, h, key)
+	typedmemmove(t.elem, p, val)
+}
+
+//go:linkname reflect_mapdelete reflect.mapdelete
+func reflect_mapdelete(t *maptype, h *hmap, key unsafe.Pointer) {
+	mapdelete(t, h, key)
+}
+
+//go:linkname reflect_mapiterinit reflect.mapiterinit
+func reflect_mapiterinit(t *maptype, h *hmap) *hiter {
+	it := new(hiter)
+	mapiterinit(t, h, it)
+	return it
+}
+
+//go:linkname reflect_mapiternext reflect.mapiternext
+func reflect_mapiternext(it *hiter) {
+	mapiternext(it)
+}
+
+//go:linkname reflect_mapiterkey reflect.mapiterkey
+func reflect_mapiterkey(it *hiter) unsafe.Pointer {
+	return it.key
+}
+
+//go:linkname reflect_maplen reflect.maplen
+func reflect_maplen(h *hmap) int {
+	if h == nil {
+		return 0
+	}
+	if raceenabled {
+		callerpc := getcallerpc()
+		racereadpc(unsafe.Pointer(h), callerpc, funcPC(reflect_maplen))
+	}
+	return h.count
+}
+
+//go:linkname reflect_ismapkey reflect.ismapkey
+func reflect_ismapkey(t *_type) bool {
+	return ismapkey(t)
+}
+
+const maxZero = 1024 // must match value in ../cmd/compile/internal/gc/walk.go
+var zeroVal [maxZero]byte