From 92c94f265c3d69c4c1f1812546ce02406df6097f Mon Sep 17 00:00:00 2001
From: Roman Khimov <roman@nspcc.ru>
Date: Mon, 6 Jun 2022 22:48:10 +0300
Subject: [PATCH] interop/vm: make VM reusable and use on VM for all in-block
 execs

Avoid allocating again and again. Increases TPS by about 3%.
---
 pkg/core/blockchain.go      | 20 ++++++++++++--------
 pkg/core/interop/context.go | 12 +++++++++++-
 pkg/vm/vm.go                | 18 ++++++++++++++++++
 3 files changed, 41 insertions(+), 9 deletions(-)

diff --git a/pkg/core/blockchain.go b/pkg/core/blockchain.go
index 6d895d8f3..694d99b33 100644
--- a/pkg/core/blockchain.go
+++ b/pkg/core/blockchain.go
@@ -1095,7 +1095,7 @@ func (bc *Blockchain) storeBlock(block *block.Block, txpool *mempool.Pool) error
 		close(aerdone)
 	}()
 	_ = cache.GetItemCtx() // Prime serialization context cache (it'll be reused by upper layer DAOs).
-	aer, err := bc.runPersist(bc.contracts.GetPersistScript(), block, cache, trigger.OnPersist)
+	aer, v, err := bc.runPersist(bc.contracts.GetPersistScript(), block, cache, trigger.OnPersist, nil)
 	if err != nil {
 		// Release goroutines, don't care about errors, we already have one.
 		close(aerchan)
@@ -1107,7 +1107,7 @@ func (bc *Blockchain) storeBlock(block *block.Block, txpool *mempool.Pool) error
 
 	for _, tx := range block.Transactions {
 		systemInterop := bc.newInteropContext(trigger.Application, cache, block, tx)
-		v := systemInterop.SpawnVM()
+		systemInterop.ReuseVM(v)
 		v.LoadScriptWithFlags(tx.Script, callflag.All)
 		v.GasLimit = tx.SystemFee
 
@@ -1143,7 +1143,7 @@ func (bc *Blockchain) storeBlock(block *block.Block, txpool *mempool.Pool) error
 		aerchan <- aer
 	}
 
-	aer, err = bc.runPersist(bc.contracts.GetPostPersistScript(), block, cache, trigger.PostPersist)
+	aer, _, err = bc.runPersist(bc.contracts.GetPostPersistScript(), block, cache, trigger.PostPersist, v)
 	if err != nil {
 		// Release goroutines, don't care about errors, we already have one.
 		close(aerchan)
@@ -1278,14 +1278,18 @@ func (bc *Blockchain) IsExtensibleAllowed(u util.Uint160) bool {
 	return n < len(us)
 }
 
-func (bc *Blockchain) runPersist(script []byte, block *block.Block, cache *dao.Simple, trig trigger.Type) (*state.AppExecResult, error) {
+func (bc *Blockchain) runPersist(script []byte, block *block.Block, cache *dao.Simple, trig trigger.Type, v *vm.VM) (*state.AppExecResult, *vm.VM, error) {
 	systemInterop := bc.newInteropContext(trig, cache, block, nil)
-	v := systemInterop.SpawnVM()
+	if v == nil {
+		v = systemInterop.SpawnVM()
+	} else {
+		systemInterop.ReuseVM(v)
+	}
 	v.LoadScriptWithFlags(script, callflag.All)
 	if err := systemInterop.Exec(); err != nil {
-		return nil, fmt.Errorf("VM has failed: %w", err)
+		return nil, v, fmt.Errorf("VM has failed: %w", err)
 	} else if _, err := systemInterop.DAO.Persist(); err != nil {
-		return nil, fmt.Errorf("can't save changes: %w", err)
+		return nil, v, fmt.Errorf("can't save changes: %w", err)
 	}
 	return &state.AppExecResult{
 		Container: block.Hash(), // application logs can be retrieved by block hash
@@ -1296,7 +1300,7 @@ func (bc *Blockchain) runPersist(script []byte, block *block.Block, cache *dao.S
 			Stack:       v.Estack().ToArray(),
 			Events:      systemInterop.Notifications,
 		},
-	}, nil
+	}, v, nil
 }
 
 func (bc *Blockchain) handleNotification(note *state.NotificationEvent, d *dao.Simple,
diff --git a/pkg/core/interop/context.go b/pkg/core/interop/context.go
index 3421afb21..f3b805132 100644
--- a/pkg/core/interop/context.go
+++ b/pkg/core/interop/context.go
@@ -326,12 +326,22 @@ func (ic *Context) SyscallHandler(_ *vm.VM, id uint32) error {
 // SpawnVM spawns a new VM with the specified gas limit and set context.VM field.
 func (ic *Context) SpawnVM() *vm.VM {
 	v := vm.NewWithTrigger(ic.Trigger)
+	ic.initVM(v)
+	return v
+}
+
+func (ic *Context) initVM(v *vm.VM) {
 	v.LoadToken = ic.LoadToken
 	v.GasLimit = -1
 	v.SyscallHandler = ic.SyscallHandler
 	v.SetPriceGetter(ic.GetPrice)
 	ic.VM = v
-	return v
+}
+
+// ReuseVM resets given VM and allows to reuse it in the current context.
+func (ic *Context) ReuseVM(v *vm.VM) {
+	v.Reset(ic.Trigger)
+	ic.initVM(v)
 }
 
 // RegisterCancelFunc adds the given function to the list of functions to be called after the VM
diff --git a/pkg/vm/vm.go b/pkg/vm/vm.go
index d7b744aed..95e03a2c1 100644
--- a/pkg/vm/vm.go
+++ b/pkg/vm/vm.go
@@ -122,6 +122,24 @@ func (v *VM) SetPriceGetter(f func(opcode.Opcode, []byte) int64) {
 	v.getPrice = f
 }
 
+// Reset allows to reuse existing VM for subsequent executions making them somewhat
+// more efficient. It reuses invocation and evaluation stacks as well as VM structure
+// itself.
+func (v *VM) Reset(t trigger.Type) {
+	v.state = NoneState
+	v.getPrice = nil
+	v.istack.elems = v.istack.elems[:0]
+	v.estack.elems = v.estack.elems[:0]
+	v.uncaughtException = nil
+	v.refs = 0
+	v.gasConsumed = 0
+	v.GasLimit = 0
+	v.SyscallHandler = nil
+	v.LoadToken = nil
+	v.trigger = t
+	v.invTree = nil
+}
+
 // GasConsumed returns the amount of GAS consumed during execution.
 func (v *VM) GasConsumed() int64 {
 	return v.gasConsumed