optimization: add back in the abi caching (#492)

* optimization: add back in the geohot abi caching

* changeset: patch

.changeset/rude-moons-kiss.md

+---
+"@eth-optimism/l2geth": patch
+---
+
+CPU Optimization by caching ABI methods

l2geth/accounts/abi/abi.go

@@ -32,6 +32,7 @@ type ABI struct {
 	Constructor Method
 	Methods     map[string]Method
 	Events      map[string]Event
+	MethodsById map[[4]byte]*Method
 }
 
 // JSON returns a parsed ABI interface and error if it failed.
@@ -120,6 +121,7 @@ func (abi *ABI) UnmarshalJSON(data []byte) error {
 		return err
 	}
 	abi.Methods = make(map[string]Method)
+	abi.MethodsById = make(map[[4]byte]*Method)
 	abi.Events = make(map[string]Event)
 	for _, field := range fields {
 		switch field.Type {
@@ -136,13 +138,17 @@ func (abi *ABI) UnmarshalJSON(data []byte) error {
 				_, ok = abi.Methods[name]
 			}
 			isConst := field.Constant || field.StateMutability == "pure" || field.StateMutability == "view"
-			abi.Methods[name] = Method{
+			method := Method{
 				Name:    name,
 				RawName: field.Name,
 				Const:   isConst,
 				Inputs:  field.Inputs,
 				Outputs: field.Outputs,
 			}
+			abi.Methods[name] = method
+			// add method to the id cache
+			sigdata := method.ID()
+			abi.MethodsById[[4]byte{sigdata[0], sigdata[1], sigdata[2], sigdata[3]}] = &method
 		case "event":
 			name := field.Name
 			_, ok := abi.Events[name]
@@ -168,12 +174,12 @@ func (abi *ABI) MethodById(sigdata []byte) (*Method, error) {
 	if len(sigdata) < 4 {
 		return nil, fmt.Errorf("data too short (%d bytes) for abi method lookup", len(sigdata))
 	}
-	for _, method := range abi.Methods {
-		if bytes.Equal(method.ID(), sigdata[:4]) {
-			return &method, nil
-		}
+
+	method, exist := abi.MethodsById[[4]byte{sigdata[0], sigdata[1], sigdata[2], sigdata[3]}]
+	if !exist {
+		return nil, fmt.Errorf("no method with id: %#x", sigdata[:4])
 	}
-	return nil, fmt.Errorf("no method with id: %#x", sigdata[:4])
+	return method, nil
 }
 
 // EventByID looks an event up by its topic hash in the