VM read-only mode: check `operation.writes` not `op.isMutating`.

`op.isMutating()` was added for checking mutating VM operation, but `operation.writes`
should be used now as it registers all mutating ops and is consistent with upstream.
Additionally, there is a new  mutating opcode `CREATE2`, but `CREATE2` has not been added to the
`op.isMutating()` set. The VM is in read-only mode when a private contract calls a public contract.

core/vm/evm.go

@@ -588,6 +588,8 @@ func (env *EVM) Push(statedb StateDB) {
 	// Quorum : the read only depth to be set up only once for the entire
 	// op code execution. This will be set first time transition from
 	// private state to public state happens
+	// statedb will be the state of the contract being called.
+	// if a private contract is calling a public contract make it readonly.
 	if !env.quorumReadOnly && env.privateState != statedb {
 		env.quorumReadOnly = true
 		env.readOnlyDepth = env.currentStateDepth

core/vm/interpreter.go

@@ -207,10 +207,6 @@ func (in *EVMInterpreter) Run(contract *Contract, input []byte, readOnly bool) (
 		// Get the memory location of pc
 		op = contract.GetOp(pc)
 
-		if in.evm.quorumReadOnly && op.isMutating() {
-			return nil, fmt.Errorf("VM in read-only mode. Mutating opcode prohibited")
-		}
-
 		if in.cfg.Debug {
 			// Capture pre-execution values for tracing.
 			logged, pcCopy, gasCopy = false, pc, contract.Gas
@@ -222,6 +218,9 @@ func (in *EVMInterpreter) Run(contract *Contract, input []byte, readOnly bool) (
 		if !operation.valid {
 			return nil, fmt.Errorf("invalid opcode 0x%x", int(op))
 		}
+		if in.evm.quorumReadOnly && operation.writes {
+			return nil, fmt.Errorf("VM in read-only mode. Mutating opcode prohibited")
+		}
 		if err := operation.validateStack(stack); err != nil {
 			return nil, err
 		}

core/vm/opcodes.go

@@ -538,13 +538,3 @@ var stringToOp = map[string]OpCode{
 func StringToOp(str string) OpCode {
 	return stringToOp[str]
 }
-
-func (op OpCode) isMutating() bool {
-	switch op {
-	// TODO(joel): REVERT?
-	case SELFDESTRUCT, CREATE, SSTORE, LOG0, LOG1, LOG2, LOG3, LOG4:
-		return true
-	default:
-		return false
-	}
-}