You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: vm_tape_nocuda.go
    path of file: ./repos/gorgonia
    
    the code of the file until where you have to start completion: // +build !cuda

package gorgonia

import (
	"github.com/pkg/errors"
	"gorgonia.org/tensor"
)

func finalizeTapeMachine(m *tapeMachine) {}

// UseCudaFor is an option for *tapeMachine. This function is NO-OP unless the program is built with the `cuda` tag.
func UseCudaFor(ops ...string) VMOpt {
	return func(m VM) {}
}

func (m *tapeMachine) getEngine(dev Device) tensor.Engine { return m.Engine }

func (instr *execOp) exec(m *tapeMachine) (err error) {
	m.logf("Executing %v. Node is: %x", instr, instr.id)
	m.enterLogScope()
	defer m.leaveLogScope()

	
    
func (instr *execOp) exec(m *tapeMachine) (err error) {
	m.logf("Executing %v. Node is: %x", instr, instr.id)
	m.enterLogScope()
	defer m.leaveLogScope()

	// Read
	m.watchedLogf("Inputs:")
	m.enterLogScope()
	var inputs []Value
	for _, reg := range instr.readFrom {
		v := m.cpumem[reg.id]
		inputs = append(inputs, v)
		m.watchedLogf(m.valueFmt, v)
	}
	m.leaveLogScope()

	// check if the destination has already been allocated
	var usePrealloc bool
	dest := instr.writeTo.id
	if m.cpumem[dest] != nil {
		usePrealloc = true
	}

	// Execute
	var v Value
	switch {
	case instr.preAllocated:
		if pd, ok := instr.op.(UsePreallocDoer); ok {
			p := m.cpumem[instr.writeTo.id]
			if v, err = pd.UsePreallocDo(p, inputs...); err != nil {
				return errors.Wrapf(err, "Happened while attempting to execute %v. Node is %x. Register was: %v ", instr, instr.id, instr.writeTo.id)
			}
		} else {
			// TODO: maybe warn?
			if v, err = instr.op.Do(inputs...); err != nil {
				return errors.Wrap(err, opDoFail)
			}
		}
	case usePrealloc:
		if pd, ok := instr.op.(UsePreallocDoer); ok {
			p := m.cpumem[instr.writeTo.id]
			if v, err = pd.UsePreallocDo(p, inputs...); err != nil {
				if v, err = instr.op.Do(inputs...); err != nil {
					return errors.Wrap(err, opDoFail)
				}
			}
		} else {
			if v, err = instr.op.Do(inputs...); err != nil {
				return errors.Wrap(err, opDoFail)
			}
		}
	case instr.useUnsafe:
		if ud, ok := instr.op.(UnsafeDoer); ok {
			if v, err = ud.UnsafeDo(inputs...); err != nil {
				return errors.Wrap(err, "Failed to carry UnsafeDo()")
			}
		} else {
			// TODO: warn?
			if v, err = instr.op.Do(inputs...); err != nil {
				return errors.Wrap(err, opDoFail)
			}
		}
	default:
		if v, err = instr.op.Do(inputs...); err != nil {
			return errors.Wrap(err, opDoFail)
		}
	}

	m.watchedLogf("Result:")
	m.enterLogScope()
	m.watchedLogf(m.valueFmt, v)
	m.leaveLogScope()
	// TODO: type and sohape checks

	// Write
	setEngine(v, m.Engine)

	m.cpumem[dest] = v
	node := m.p.g.Node(instr.id).(*Node)

	if m.trace() && (len(m.watchNodes) == 0 || m.watchNodes.Contains(node)) {
		if err = node.bindCopy(v); err != nil {
			return errors.Wrapf(err, "TraceExec failed to bind copy")
		}
		// Iop is special
		if node.op == (Iop{}) {
			v = node.Value()
			m.cpumem[dest] = v
		}

	} else {
		node.bind(v)
	}

	// this is a gradient node then, we should also bind the value to the node's dualValue
	if m.bindDV() && node.derivOf != nil {
		for _, src := range node.derivOf {
			if len(m.bindNodesDV) > 0 && !m.bindNodesDV.Contains(src) {
				continue
			}

			switch {
			case node.op == (Iop{}):
				// we'll need to put a closure into the closure queue
				closure := func() error {
					dv := dvUnit(src.boundTo)
					add := newEBOByType(addOpType, TypeOf(dv.d), TypeOf(v))
					if _, err := add.UnsafeDo(dv.d, v); err != nil {
						return err
					}
					return nil
				}
				m.closureQueue = append(m.closureQueue, closure)
			default:
				// TODO HERE
				/*
				   e.g. problem
				   z = y * (x + 1)

				   Here, 1 is a constant. But 1 comes early in the expression graph.
				   The final gradient is also 1, so 1 will also be the derivOf `z`
				   But because the graph is sorted, the 1 node will be walked before
				   the `z` node, and this part will cause a panic, as `z` will have no `Value`
				   associated with it yet.
				*/
				dv := dvUnit(src.boundTo)
				add := newEBOByType(addOpType, TypeOf(dv.d), TypeOf(v))

				if d, err := add.UnsafeDo(dv.d, v); err == nil {
					dv.SetDeriv(d)
					src.bind(dv)
				} else {
					return err
				}
			}

		}

	}

	m.watchedLogf("Written To: %v", instr.writeTo)
	m.enterLogScope()
	m.watchedLogf(m.valueFmt, v)
	m.leaveLogScope()
	return nil
}