Improved SSA and added unused value checks

src/core/CheckDeadCode.go

@@ -0,0 +1,16 @@
+package core
+
+import (
+	"git.urbach.dev/cli/q/src/errors"
+)
+
+// CheckDeadCode checks for dead values.
+func (f *Function) CheckDeadCode() error {
+	for instr := range f.Values {
+		if instr.IsConst() && instr.Alive() == 0 {
+			return errors.New(&UnusedValue{Value: instr.String()}, f.File, instr.Token().Position)
+		}
+	}
+
+	return nil
+}

src/core/Compile.go

@@ -26,4 +26,6 @@ func (f *Function) Compile() {
 			return
 		}
 	}
+
+	f.Err = f.CheckDeadCode()
 }

src/core/CompileReturn.go

@@ -15,9 +15,10 @@ func (f *Function) CompileReturn(tokens token.List) error {
 		return err
 	}
 
-	f.Append(ssa.Value{
-		Type: ssa.Return,
-		Args: []*ssa.Value{value},
+	f.Append(&ssa.Return{
+		Arguments: ssa.Arguments{
+			Args: []ssa.Value{value},
+		},
 	})
 
 	return nil

src/core/Evaluate.go

@@ -10,7 +10,7 @@ import (
 )
 
 // Evaluate converts an expression to an SSA value.
-func (f *Function) Evaluate(expr *expression.Expression) (*ssa.Value, error) {
+func (f *Function) Evaluate(expr *expression.Expression) (ssa.Value, error) {
 	if expr.IsLeaf() {
 		switch expr.Token.Kind {
 		case token.Identifier:
@@ -30,12 +30,16 @@ func (f *Function) Evaluate(expr *expression.Expression) (*ssa.Value, error) {
 				return nil, err
 			}
 
-			return f.AppendInt(number), nil
+			v := f.AppendInt(number)
+			v.Source = expr.Token
+			return v, nil
 
 		case token.String:
 			data := expr.Token.Bytes(f.File.Bytes)
 			data = Unescape(data)
-			return f.AppendBytes(data), nil
+			v := f.AppendBytes(data)
+			v.Source = expr.Token
+			return v, nil
 		}
 
 		return nil, errors.New(InvalidExpression, f.File, expr.Token.Position)
@@ -44,7 +48,7 @@ func (f *Function) Evaluate(expr *expression.Expression) (*ssa.Value, error) {
 	switch expr.Token.Kind {
 	case token.Call:
 		children := expr.Children
-		typ := ssa.Call
+		isSyscall := false
 
 		if children[0].Token.Kind == token.Identifier {
 			funcName := children[0].String(f.File.Bytes)
@@ -56,11 +60,11 @@ func (f *Function) Evaluate(expr *expression.Expression) (*ssa.Value, error) {
 
 			if funcName == "syscall" {
 				children = children[1:]
-				typ = ssa.Syscall
+				isSyscall = true
 			}
 		}
 
-		args := make([]*ssa.Value, len(children))
+		args := make([]ssa.Value, len(children))
 
 		for i, child := range children {
 			value, err := f.Evaluate(child)
@@ -72,12 +76,27 @@ func (f *Function) Evaluate(expr *expression.Expression) (*ssa.Value, error) {
 			args[i] = value
 		}
 
-		call := f.Append(ssa.Value{Type: typ, Args: args})
-		return call, nil
+		if isSyscall {
+			v := f.Append(&ssa.Syscall{
+				Arguments: ssa.Arguments{Args: args},
+				HasToken:  ssa.HasToken{Source: expr.Token},
+			})
+
+			return v, nil
+		} else {
+			v := f.Append(&ssa.Call{
+				Arguments: ssa.Arguments{Args: args},
+				HasToken:  ssa.HasToken{Source: expr.Token},
+			})
+
+			return v, nil
+		}
 
 	case token.Dot:
 		name := fmt.Sprintf("%s.%s", expr.Children[0].String(f.File.Bytes), expr.Children[1].String(f.File.Bytes))
-		return f.AppendFunction(name), nil
+		v := f.AppendFunction(name)
+		v.Source = expr.Children[1].Token
+		return v, nil
 	}
 
 	return nil, nil

src/core/Function.go

@@ -10,14 +10,14 @@ import (
 
 // Function is the smallest unit of code.
 type Function struct {
-	ssa.Function
+	ssa.IR
 	Name        string
 	UniqueName  string
 	File        *fs.File
 	Input       []*Parameter
 	Output      []*Parameter
 	Body        token.List
-	Identifiers map[string]*ssa.Value
+	Identifiers map[string]ssa.Value
 	Err         error
 }
 
@@ -27,9 +27,11 @@ func NewFunction(name string, file *fs.File) *Function {
 		Name:        name,
 		File:        file,
 		UniqueName:  fmt.Sprintf("%s.%s", file.Package, name),
-		Identifiers: make(map[string]*ssa.Value),
-		Function: ssa.Function{
-			Blocks: []*ssa.Block{{}},
+		Identifiers: make(map[string]ssa.Value),
+		IR: ssa.IR{
+			Blocks: []*ssa.Block{
+				{Instructions: make([]ssa.Value, 0, 8)},
+			},
 		},
 	}
 }

src/core/errors.go

@@ -25,3 +25,12 @@ func (err *UnknownIdentifier) Error() string {
 
 	return fmt.Sprintf("Unknown identifier '%s'", err.Name)
 }
+
+// UnusedValue error is created when a value is never used.
+type UnusedValue struct {
+	Value string
+}
+
+func (err *UnusedValue) Error() string {
+	return fmt.Sprintf("Unused value '%s'", err.Value)
+}

src/expression/operator.go

@@ -13,9 +13,9 @@ type operator struct {
 	Operands   int8
 }
 
-// operators defines the operators used in the language.
+// Operators defines the Operators used in the language.
 // The number corresponds to the operator priority and can not be zero.
-var operators = [64]operator{
+var Operators = [64]operator{
 	token.Dot:    {".", 13, 2},
 	token.Call:   {"λ", 12, 1},
 	token.Array:  {"@", 12, 2},
@@ -59,9 +59,9 @@ var operators = [64]operator{
 }
 
 func numOperands(symbol token.Kind) int {
-	return int(operators[symbol].Operands)
+	return int(Operators[symbol].Operands)
 }
 
 func precedence(symbol token.Kind) int8 {
-	return operators[symbol].Precedence
+	return Operators[symbol].Precedence
 }

src/expression/write.go

@@ -17,9 +17,9 @@ func (expr *Expression) write(builder *strings.Builder, source []byte) {
 
 	switch expr.Token.Kind {
 	case token.Call:
-		builder.WriteString(operators[token.Call].Symbol)
+		builder.WriteString(Operators[token.Call].Symbol)
 	case token.Array:
-		builder.WriteString(operators[token.Array].Symbol)
+		builder.WriteString(Operators[token.Array].Symbol)
 	default:
 		builder.WriteString(expr.Token.String(source))
 	}

src/ssa/Arguments.go

@@ -0,0 +1,23 @@
+package ssa
+
+type Arguments struct {
+	Args []Value
+}
+
+func (v *Arguments) Dependencies() []Value {
+	return v.Args
+}
+
+func (a Arguments) Equals(b Arguments) bool {
+	if len(a.Args) != len(b.Args) {
+		return false
+	}
+
+	for i := range a.Args {
+		if !a.Args[i].Equals(b.Args[i]) {
+			return false
+		}
+	}
+
+	return true
+}

src/ssa/BinaryOperation.go

@@ -0,0 +1,50 @@
+package ssa
+
+import (
+	"fmt"
+
+	"git.urbach.dev/cli/q/src/expression"
+	"git.urbach.dev/cli/q/src/token"
+)
+
+type BinaryOperation struct {
+	Left  Value
+	Right Value
+	Op    token.Kind
+	Liveness
+	HasToken
+}
+
+func (v *BinaryOperation) Dependencies() []Value {
+	return []Value{v.Left, v.Right}
+}
+
+func (a *BinaryOperation) Equals(v Value) bool {
+	b, sameType := v.(*BinaryOperation)
+
+	if !sameType {
+		return false
+	}
+
+	if a.Source.Kind != b.Source.Kind {
+		return false
+	}
+
+	if !a.Left.Equals(b.Left) {
+		return false
+	}
+
+	if !a.Right.Equals(b.Right) {
+		return false
+	}
+
+	return true
+}
+
+func (v *BinaryOperation) IsConst() bool {
+	return true
+}
+
+func (v *BinaryOperation) String() string {
+	return fmt.Sprintf("%s %s %s", v.Left, expression.Operators[v.Op].Symbol, v.Right)
+}

src/ssa/Block.go

@@ -6,7 +6,11 @@ type Block struct {
 }
 
 // Append adds a new instruction to the block.
-func (b *Block) Append(instr Value) *Value {
-	b.Instructions = append(b.Instructions, instr)
-	return &b.Instructions[len(b.Instructions)-1]
+func (block *Block) Append(instr Value) Value {
+	for _, dep := range instr.Dependencies() {
+		dep.AddUse(instr)
+	}
+
+	block.Instructions = append(block.Instructions, instr)
+	return instr
 }

src/ssa/Bytes.go

@@ -0,0 +1,31 @@
+package ssa
+
+import "bytes"
+
+type Bytes struct {
+	Bytes []byte
+	Liveness
+	HasToken
+}
+
+func (v *Bytes) Dependencies() []Value {
+	return nil
+}
+
+func (a *Bytes) Equals(v Value) bool {
+	b, sameType := v.(*Bytes)
+
+	if !sameType {
+		return false
+	}
+
+	return bytes.Equal(a.Bytes, b.Bytes)
+}
+
+func (v *Bytes) IsConst() bool {
+	return true
+}
+
+func (v *Bytes) String() string {
+	return string(v.Bytes)
+}

src/ssa/Call.go

@@ -0,0 +1,27 @@
+package ssa
+
+import "fmt"
+
+type Call struct {
+	Arguments
+	Liveness
+	HasToken
+}
+
+func (a *Call) Equals(v Value) bool {
+	b, sameType := v.(*Call)
+
+	if !sameType {
+		return false
+	}
+
+	return a.Arguments.Equals(b.Arguments)
+}
+
+func (v *Call) IsConst() bool {
+	return false
+}
+
+func (v *Call) String() string {
+	return fmt.Sprintf("call%v", v.Args)
+}

src/ssa/Function.go

@@ -1,61 +1,29 @@
 package ssa
 
-import (
-	"git.urbach.dev/cli/q/src/cpu"
-)
-
-// Function is a list of basic blocks.
 type Function struct {
-	Blocks []*Block
+	UniqueName string
+	Liveness
+	HasToken
 }
 
-// AddBlock adds a new block to the function.
-func (f *Function) AddBlock() *Block {
-	block := &Block{}
-	f.Blocks = append(f.Blocks, block)
-	return block
+func (v *Function) Dependencies() []Value {
+	return nil
 }
 
-// Append adds a new value to the last block.
-func (f *Function) Append(instr Value) *Value {
-	if len(f.Blocks) == 0 {
-		f.Blocks = append(f.Blocks, &Block{})
+func (a *Function) Equals(v Value) bool {
+	b, sameType := v.(*Function)
+
+	if !sameType {
+		return false
 	}
 
-	if instr.IsConst() {
-		for _, b := range f.Blocks {
-			for _, existing := range b.Instructions {
-				if instr.Equals(existing) {
-					return &existing
-				}
-			}
-		}
-	}
-
-	return f.Blocks[len(f.Blocks)-1].Append(instr)
+	return a.UniqueName == b.UniqueName
 }
 
-// AppendInt adds a new integer value to the last block.
-func (f *Function) AppendInt(x int) *Value {
-	return f.Append(Value{Type: Int, Int: x})
+func (v *Function) IsConst() bool {
+	return true
 }
 
-// AppendRegister adds a new register value to the last block.
-func (f *Function) AppendRegister(reg cpu.Register) *Value {
-	return f.Append(Value{Type: Register, Register: reg})
-}
-
-// AppendFunction adds a new function value to the last block.
-func (f *Function) AppendFunction(name string) *Value {
-	return f.Append(Value{Type: Func, Text: name})
-}
-
-// AppendBytes adds a new byte slice value to the last block.
-func (f *Function) AppendBytes(s []byte) *Value {
-	return f.Append(Value{Type: String, Text: string(s)})
-}
-
-// AppendString adds a new string value to the last block.
-func (f *Function) AppendString(s string) *Value {
-	return f.Append(Value{Type: String, Text: s})
+func (v *Function) String() string {
+	return v.UniqueName
 }

src/ssa/HasToken.go

@@ -0,0 +1,11 @@
+package ssa
+
+import "git.urbach.dev/cli/q/src/token"
+
+type HasToken struct {
+	Source token.Token
+}
+
+func (v *HasToken) Token() token.Token {
+	return v.Source
+}

src/ssa/IR.go

@@ -0,0 +1,83 @@
+package ssa
+
+import (
+	"git.urbach.dev/cli/q/src/cpu"
+)
+
+// IR is a list of basic blocks.
+type IR struct {
+	Blocks []*Block
+}
+
+// AddBlock adds a new block to the function.
+func (f *IR) AddBlock() *Block {
+	block := &Block{
+		Instructions: make([]Value, 0, 8),
+	}
+
+	f.Blocks = append(f.Blocks, block)
+	return block
+}
+
+// Append adds a new value to the last block.
+func (f *IR) Append(instr Value) Value {
+	if len(f.Blocks) == 0 {
+		f.AddBlock()
+	}
+
+	if instr.IsConst() {
+		for existing := range f.Values {
+			if existing.IsConst() && instr.Equals(existing) {
+				return existing
+			}
+		}
+	}
+
+	return f.Blocks[len(f.Blocks)-1].Append(instr)
+}
+
+// AppendInt adds a new integer value to the last block.
+func (f *IR) AppendInt(x int) *Int {
+	v := &Int{Int: x}
+	f.Append(v)
+	return v
+}
+
+// AppendRegister adds a new register value to the last block.
+func (f *IR) AppendRegister(reg cpu.Register) *Register {
+	v := &Register{Register: reg}
+	f.Append(v)
+	return v
+}
+
+// AppendFunction adds a new function value to the last block.
+func (f *IR) AppendFunction(name string) *Function {
+	v := &Function{UniqueName: name}
+	f.Append(v)
+	return v
+}
+
+// AppendBytes adds a new byte slice value to the last block.
+func (f *IR) AppendBytes(s []byte) *Bytes {
+	v := &Bytes{Bytes: s}
+	f.Append(v)
+	return v
+}
+
+// AppendString adds a new string value to the last block.
+func (f *IR) AppendString(s string) *Bytes {
+	v := &Bytes{Bytes: []byte(s)}
+	f.Append(v)
+	return v
+}
+
+// Values yields on each value.
+func (f *IR) Values(yield func(Value) bool) {
+	for _, block := range f.Blocks {
+		for _, instr := range block.Instructions {
+			if !yield(instr) {
+				return
+			}
+		}
+	}
+}

src/ssa/Int.go

@@ -0,0 +1,33 @@
+package ssa
+
+import (
+	"fmt"
+)
+
+type Int struct {
+	Int int
+	Liveness
+	HasToken
+}
+
+func (v *Int) Dependencies() []Value {
+	return nil
+}
+
+func (a *Int) Equals(v Value) bool {
+	b, sameType := v.(*Int)
+
+	if !sameType {
+		return false
+	}
+
+	return a.Int == b.Int
+}
+
+func (v *Int) IsConst() bool {
+	return true
+}
+
+func (v *Int) String() string {
+	return fmt.Sprintf("%d", v.Int)
+}

src/ssa/Liveness.go

@@ -0,0 +1,13 @@
+package ssa
+
+type Liveness struct {
+	alive int
+}
+
+func (v *Liveness) AddUse(user Value) {
+	v.alive++
+}
+
+func (v *Liveness) Alive() int {
+	return v.alive
+}

src/ssa/Register.go

@@ -0,0 +1,31 @@
+package ssa
+
+import "git.urbach.dev/cli/q/src/cpu"
+
+type Register struct {
+	Register cpu.Register
+	Liveness
+	HasToken
+}
+
+func (v *Register) Dependencies() []Value {
+	return nil
+}
+
+func (a *Register) Equals(v Value) bool {
+	b, sameType := v.(*Register)
+
+	if !sameType {
+		return false
+	}
+
+	return a.Register == b.Register
+}
+
+func (v *Register) IsConst() bool {
+	return true
+}
+
+func (v *Register) String() string {
+	return v.Register.String()
+}

src/ssa/Return.go

@@ -0,0 +1,39 @@
+package ssa
+
+import "fmt"
+
+type Return struct {
+	Arguments
+	HasToken
+}
+
+func (a *Return) AddUse(user Value) { panic("return is not a value") }
+func (a *Return) Alive() int        { return 0 }
+
+func (a *Return) Equals(v Value) bool {
+	b, sameType := v.(*Return)
+
+	if !sameType {
+		return false
+	}
+
+	if len(a.Args) != len(b.Args) {
+		return false
+	}
+
+	for i := range a.Args {
+		if !a.Args[i].Equals(b.Args[i]) {
+			return false
+		}
+	}
+
+	return true
+}
+
+func (v *Return) IsConst() bool {
+	return false
+}
+
+func (v *Return) String() string {
+	return fmt.Sprintf("return %v", v.Args)
+}

src/ssa/Syscall.go

@@ -0,0 +1,27 @@
+package ssa
+
+import "fmt"
+
+type Syscall struct {
+	Arguments
+	Liveness
+	HasToken
+}
+
+func (a *Syscall) Equals(v Value) bool {
+	b, sameType := v.(*Syscall)
+
+	if !sameType {
+		return false
+	}
+
+	return a.Arguments.Equals(b.Arguments)
+}
+
+func (v *Syscall) IsConst() bool {
+	return false
+}
+
+func (v *Syscall) String() string {
+	return fmt.Sprintf("syscall%v", v.Args)
+}

src/ssa/Type.go

@@ -1,39 +0,0 @@
-package ssa
-
-// Type represents the instruction type.
-type Type byte
-
-const (
-	None Type = iota
-
-	// Values
-	Int
-	Float
-	Func
-	Register
-	String
-
-	// Binary
-	Add
-	Sub
-	Mul
-	Div
-	Mod
-
-	// Bitwise
-	And
-	Or
-	Xor
-	Shl
-	Shr
-
-	// Control flow
-	If
-	Jump
-	Call
-	Return
-	Syscall
-
-	// Special
-	Phi
-)

src/ssa/Value.go

@@ -1,83 +1,13 @@
 package ssa
 
-import (
-	"fmt"
+import "git.urbach.dev/cli/q/src/token"
 
-	"git.urbach.dev/cli/q/src/cpu"
-)
-
-// Value is a single instruction in a basic block.
-// It is implemented as a "fat struct" for performance reasons.
-// It contains all the fields necessary to represent all instruction types.
-type Value struct {
-	Args     []*Value
-	Int      int
-	Text     string
-	Register cpu.Register
-	Type     Type
-}
-
-// Equals returns true if the values are equal.
-func (a Value) Equals(b Value) bool {
-	if a.Type != b.Type {
-		return false
-	}
-
-	if a.Int != b.Int {
-		return false
-	}
-
-	if a.Text != b.Text {
-		return false
-	}
-
-	if a.Register != b.Register {
-		return false
-	}
-
-	if len(a.Args) != len(b.Args) {
-		return false
-	}
-
-	for i := range a.Args {
-		if !a.Args[i].Equals(*b.Args[i]) {
-			return false
-		}
-	}
-
-	return true
-}
-
-// IsConst returns true if the value is constant.
-func (i *Value) IsConst() bool {
-	switch i.Type {
-	case Func, Int, Register, String:
-		return true
-	default:
-		return false
-	}
-}
-
-// String returns a human-readable representation of the instruction.
-func (i *Value) String() string {
-	switch i.Type {
-	case Func:
-		return i.Text
-	case Int:
-		return fmt.Sprintf("%d", i.Int)
-	case Register:
-		return i.Register.String()
-	case String:
-		return fmt.Sprintf("\"%s\"", i.Text)
-	case Add:
-		return fmt.Sprintf("%s + %s", i.Args[0], i.Args[1])
-	case Return:
-		return fmt.Sprintf("return %s", i.Args[0])
-	case Call:
-		return fmt.Sprintf("call%v", i.Args)
-	case Syscall:
-		return fmt.Sprintf("syscall%v", i.Args)
-	default:
-		return ""
-	}
+type Value interface {
+	AddUse(Value)
+	Alive() int
+	Dependencies() []Value
+	Equals(Value) bool
+	IsConst() bool
+	String() string
+	Token() token.Token
 }

src/ssa/bench_test.go

@@ -5,12 +5,16 @@ import (
 	"runtime/debug"
 	"testing"
 
+	"git.urbach.dev/cli/q/src/ssa"
 	"git.urbach.dev/go/assert"
 )
 
 // This benchmark compares the performance of fat structs and interfaces.
-// It allocates `n` objects where `n` must be divisible by 2.
-const n = 100
+// It allocates `actual` objects where `actual` must be divisible by 2.
+const (
+	actual   = 64
+	estimate = 8
+)
 
 type FatStruct struct {
 	Type byte
@@ -45,9 +49,9 @@ func TestMain(m *testing.M) {
 
 func BenchmarkFatStructRaw(b *testing.B) {
 	for b.Loop() {
-		entries := make([]FatStruct, 0, n)
+		entries := make([]FatStruct, 0, estimate)
 
-		for i := range n {
+		for i := range actual {
 			entries = append(entries, FatStruct{
 				Type: byte(i % 2),
 				A:    i,
@@ -65,15 +69,15 @@ func BenchmarkFatStructRaw(b *testing.B) {
 			}
 		}
 
-		assert.Equal(b, count, n/2)
+		assert.Equal(b, count, actual/2)
 	}
 }
 
 func BenchmarkFatStructPtr(b *testing.B) {
 	for b.Loop() {
-		entries := make([]*FatStruct, 0, n)
+		entries := make([]*FatStruct, 0, estimate)
 
-		for i := range n {
+		for i := range actual {
 			entries = append(entries, &FatStruct{
 				Type: byte(i % 2),
 				A:    i,
@@ -91,15 +95,15 @@ func BenchmarkFatStructPtr(b *testing.B) {
 			}
 		}
 
-		assert.Equal(b, count, n/2)
+		assert.Equal(b, count, actual/2)
 	}
 }
 
 func BenchmarkInterfaceRaw(b *testing.B) {
 	for b.Loop() {
-		entries := make([]Instruction, 0, n)
+		entries := make([]Instruction, 0, estimate)
 
-		for i := range n {
+		for i := range actual {
 			if i%2 == 0 {
 				entries = append(entries, BinaryInstruction{
 					A: i,
@@ -123,15 +127,15 @@ func BenchmarkInterfaceRaw(b *testing.B) {
 			}
 		}
 
-		assert.Equal(b, count, n/2)
+		assert.Equal(b, count, actual/2)
 	}
 }
 
 func BenchmarkInterfacePtr(b *testing.B) {
 	for b.Loop() {
-		entries := make([]Instruction, 0, n)
+		entries := make([]Instruction, 0, estimate)
 
-		for i := range n {
+		for i := range actual {
 			if i%2 == 0 {
 				entries = append(entries, &BinaryInstruction{
 					A: i,
@@ -155,6 +159,32 @@ func BenchmarkInterfacePtr(b *testing.B) {
 			}
 		}
 
-		assert.Equal(b, count, n/2)
+		assert.Equal(b, count, actual/2)
+	}
+}
+
+func BenchmarkSSA(b *testing.B) {
+	for b.Loop() {
+		f := ssa.IR{}
+
+		for i := range actual {
+			if i%2 == 0 {
+				f.Append(&ssa.Return{})
+			} else {
+				f.Append(&ssa.Call{})
+			}
+		}
+
+		count := 0
+
+		for instr := range f.Values {
+			switch instr.(type) {
+			case *ssa.Return:
+				count++
+			case *ssa.Call:
+			}
+		}
+
+		assert.Equal(b, count, actual/2)
 	}
 }

src/ssa/ssa_test.go

@@ -4,23 +4,19 @@ import (
 	"testing"
 
 	"git.urbach.dev/cli/q/src/ssa"
+	"git.urbach.dev/cli/q/src/token"
 	"git.urbach.dev/go/assert"
 )
 
 func TestFunction(t *testing.T) {
-	fn := ssa.Function{}
+	fn := ssa.IR{}
 	a := fn.AppendInt(1)
 	b := fn.AppendInt(2)
-	c := fn.Append(ssa.Value{Type: ssa.Add, Args: []*ssa.Value{a, b}})
+	c := fn.Append(&ssa.BinaryOperation{Op: token.Add, Left: a, Right: b})
 	fn.AddBlock()
 	d := fn.AppendInt(3)
 	e := fn.AppendInt(4)
-	f := fn.Append(ssa.Value{Type: ssa.Add, Args: []*ssa.Value{d, e}})
+	f := fn.Append(&ssa.BinaryOperation{Op: token.Add, Left: d, Right: e})
 	assert.Equal(t, c.String(), "1 + 2")
 	assert.Equal(t, f.String(), "3 + 4")
 }
-
-func TestInvalidInstruction(t *testing.T) {
-	instr := ssa.Value{}
-	assert.Equal(t, instr.String(), "")
-}