Merge pull request #572 from nspcc-dev/tiny-vm-and-core-speedups

This eliminates some easy to fix blocks, but the overall improvement is on the order
of ~1-2%, so it's hardly visible in a 100K block import test. Still, it slightly reduces
the DB pressure and eliminates useless hashing, so it's nice to have.

pkg/core/blockchain.go

@@ -55,6 +55,9 @@ type Blockchain struct {
 	// Write access should only happen in storeBlock().
 	blockHeight uint32
 
+	// Current top Block wrapped in an atomic.Value for safe access.
+	topBlock atomic.Value
+
 	// Current persisted block count.
 	persistedHeight uint32
 
@@ -558,6 +561,7 @@ func (bc *Blockchain) storeBlock(block *Block) error {
 	if err != nil {
 		return err
 	}
+	bc.topBlock.Store(block)
 	atomic.StoreUint32(&bc.blockHeight, block.Index)
 	updateBlockHeightMetric(block.Index)
 	for _, tx := range block.Transactions {
@@ -749,6 +753,13 @@ func (bc *Blockchain) GetStorageItems(hash util.Uint160) (map[string]*state.Stor
 
 // GetBlock returns a Block by the given hash.
 func (bc *Blockchain) GetBlock(hash util.Uint256) (*Block, error) {
+	topBlock := bc.topBlock.Load()
+	if topBlock != nil {
+		if tb, ok := topBlock.(*Block); ok && tb.Hash().Equals(hash) {
+			return tb, nil
+		}
+	}
+
 	block, err := bc.dao.GetBlock(hash)
 	if err != nil {
 		return nil, err
@@ -768,6 +779,12 @@ func (bc *Blockchain) GetBlock(hash util.Uint256) (*Block, error) {
 
 // GetHeader returns data block header identified with the given hash value.
 func (bc *Blockchain) GetHeader(hash util.Uint256) (*Header, error) {
+	topBlock := bc.topBlock.Load()
+	if topBlock != nil {
+		if tb, ok := topBlock.(*Block); ok && tb.Hash().Equals(hash) {
+			return tb.Header(), nil
+		}
+	}
 	block, err := bc.dao.GetBlock(hash)
 	if err != nil {
 		return nil, err

pkg/vm/vm.go

@@ -238,6 +238,14 @@ func (v *VM) LoadScript(b []byte) {
 	v.istack.PushVal(ctx)
 }
 
+// loadScriptWithHash if similar to the LoadScript method, but it also loads
+// given script hash directly into the Context to avoid its recalculations. It's
+// up to user of this function to make sure the script and hash match each other.
+func (v *VM) loadScriptWithHash(b []byte, hash util.Uint160) {
+	v.LoadScript(b)
+	v.istack.Top().Value().(*Context).scriptHash = hash
+}
+
 // Context returns the current executed context. Nil if there is no context,
 // which implies no program is loaded.
 func (v *VM) Context() *Context {
@@ -1120,7 +1128,7 @@ func (v *VM) execute(ctx *Context, op opcode.Opcode, parameter []byte) (err erro
 			_ = v.istack.Pop()
 		}
 
-		v.LoadScript(script)
+		v.loadScriptWithHash(script, hash)
 
 	case opcode.RET:
 		oldCtx := v.istack.Pop().Value().(*Context)
@@ -1336,6 +1344,7 @@ func (v *VM) execute(ctx *Context, op opcode.Opcode, parameter []byte) (err erro
 				panic(fmt.Sprintf("could not find script %s", hash))
 			}
 			newCtx = NewContext(script)
+			newCtx.scriptHash = hash
 		}
 		newCtx.rvcount = rvcount
 		newCtx.estack = NewStack("evaluation")