compiler, runtime: implement delete builtin

src/runtime/hashmap.go

@@ -158,6 +158,41 @@ func hashmapGet(m *hashmap, key unsafe.Pointer, value unsafe.Pointer, hash uint3
 	memzero(value, uintptr(m.valueSize))
 }
 
+// Delete a given key from the map. No-op when the key does not exist in the
+// map.
+//go:nobounds
+func hashmapDelete(m *hashmap, key unsafe.Pointer, hash uint32, keyEqual func(x, y unsafe.Pointer, n uintptr) bool) {
+	numBuckets := uintptr(1) << m.bucketBits
+	bucketNumber := (uintptr(hash) & (numBuckets - 1))
+	bucketSize := unsafe.Sizeof(hashmapBucket{}) + uintptr(m.keySize)*8 + uintptr(m.valueSize)*8
+	bucketAddr := uintptr(m.buckets) + bucketSize*bucketNumber
+	bucket := (*hashmapBucket)(unsafe.Pointer(bucketAddr))
+
+	tophash := uint8(hash >> 24)
+	if tophash < 1 {
+		// 0 means empty slot, so make it bigger.
+		tophash += 1
+	}
+
+	// Try to find the key.
+	for bucket != nil {
+		for i := uintptr(0); i < 8; i++ {
+			slotKeyOffset := unsafe.Sizeof(hashmapBucket{}) + uintptr(m.keySize)*uintptr(i)
+			slotKey := unsafe.Pointer(uintptr(unsafe.Pointer(bucket)) + slotKeyOffset)
+			if bucket.tophash[i] == tophash {
+				// This could be the key we're looking for.
+				if keyEqual(key, slotKey, uintptr(m.keySize)) {
+					// Found the key, delete it.
+					bucket.tophash[i] = 0
+					m.count--
+					return
+				}
+			}
+		}
+		bucket = bucket.next
+	}
+}
+
 // Iterate over a hashmap.
 //go:nobounds
 func hashmapNext(m *hashmap, it *hashmapIterator, key, value unsafe.Pointer) bool {
@@ -209,6 +244,11 @@ func hashmapBinaryGet(m *hashmap, key, value unsafe.Pointer) {
 	hashmapGet(m, key, value, hash, memequal)
 }
 
+func hashmapBinaryDelete(m *hashmap, key unsafe.Pointer) {
+	hash := hashmapHash(key, uintptr(m.keySize))
+	hashmapDelete(m, key, hash, memequal)
+}
+
 // Hashmap with string keys (a common case).
 
 func hashmapStringEqual(x, y unsafe.Pointer, n uintptr) bool {
@@ -229,3 +269,8 @@ func hashmapStringGet(m *hashmap, key string, value unsafe.Pointer) {
 	hash := hashmapStringHash(key)
 	hashmapGet(m, unsafe.Pointer(&key), value, hash, hashmapStringEqual)
 }
+
+func hashmapStringDelete(m *hashmap, key string) {
+	hash := hashmapStringHash(key)
+	hashmapDelete(m, unsafe.Pointer(&key), hash, hashmapStringEqual)
+}