diff --git a/internal/shader/shader.go b/internal/shader/shader.go
index 3f80cd9eb..0f513dfb7 100644
--- a/internal/shader/shader.go
+++ b/internal/shader/shader.go
@@ -92,7 +92,7 @@ type block struct {
 	pos    token.Pos
 	outer  *block
 
-	ir shaderir.Block
+	ir *shaderir.Block
 }
 
 func (b *block) findLocalVariable(name string) (int, shaderir.Type, bool) {
@@ -140,6 +140,7 @@ func Compile(fs *token.FileSet, f *ast.File, vertexEntry, fragmentEntry string,
 		vertexEntry:   vertexEntry,
 		fragmentEntry: fragmentEntry,
 	}
+	s.global.ir = &shaderir.Block{}
 	s.parse(f)
 
 	if len(s.errs) > 0 {
@@ -221,6 +222,7 @@ func (cs *compileState) parse(f *ast.File) {
 				Index:     len(cs.funcs),
 				InParams:  inT,
 				OutParams: outT,
+				Block:     &shaderir.Block{},
 			},
 		})
 	}
@@ -657,7 +659,9 @@ func (cs *compileState) parseBlock(outer *block, stmts []ast.Stmt, inParams, out
 	block := &block{
 		vars:  vars,
 		outer: outer,
+		ir:    &shaderir.Block{},
 	}
+
 	defer func() {
 		var offset int
 		if outer == &cs.global {
diff --git a/internal/shader/stmt.go b/internal/shader/stmt.go
index c9f113c60..04248c55b 100644
--- a/internal/shader/stmt.go
+++ b/internal/shader/stmt.go
@@ -103,7 +103,7 @@ func (cs *compileState) parseStmt(block *block, stmt ast.Stmt, inParams []variab
 		}
 		stmts = append(stmts, shaderir.Stmt{
 			Type: shaderir.BlockStmt,
-			Blocks: []shaderir.Block{
+			Blocks: []*shaderir.Block{
 				b.ir,
 			},
 		})
@@ -261,7 +261,7 @@ func (cs *compileState) parseStmt(block *block, stmt ast.Stmt, inParams []variab
 
 		stmts = append(stmts, shaderir.Stmt{
 			Type:        shaderir.For,
-			Blocks:      []shaderir.Block{bodyir},
+			Blocks:      []*shaderir.Block{bodyir},
 			ForVarType:  vartype,
 			ForVarIndex: varidx,
 			ForInit:     init,
@@ -281,7 +281,7 @@ func (cs *compileState) parseStmt(block *block, stmt ast.Stmt, inParams []variab
 
 			stmts = append(stmts, shaderir.Stmt{
 				Type:   shaderir.BlockStmt,
-				Blocks: []shaderir.Block{b.ir},
+				Blocks: []*shaderir.Block{b.ir},
 			})
 			return stmts, true
 		}
@@ -300,7 +300,7 @@ func (cs *compileState) parseStmt(block *block, stmt ast.Stmt, inParams []variab
 		}
 		stmts = append(stmts, ss...)
 
-		var bs []shaderir.Block
+		var bs []*shaderir.Block
 		b, ok := cs.parseBlock(block, stmt.Body.List, inParams, nil)
 		if !ok {
 			return nil, false
diff --git a/internal/shaderir/glsl/glsl.go b/internal/shaderir/glsl/glsl.go
index 58805ff26..b9c672c50 100644
--- a/internal/shaderir/glsl/glsl.go
+++ b/internal/shaderir/glsl/glsl.go
@@ -88,10 +88,10 @@ func Compile(p *shaderir.Program) (vertexShader, fragmentShader string) {
 			}
 		}
 
-		if len(p.VertexFunc.Block.Stmts) > 0 {
+		if p.VertexFunc.Block != nil && len(p.VertexFunc.Block.Stmts) > 0 {
 			vslines = append(vslines, "")
 			vslines = append(vslines, "void main(void) {")
-			vslines = append(vslines, c.glslBlock(p, &p.VertexFunc.Block, &p.VertexFunc.Block, 0, 0)...)
+			vslines = append(vslines, c.glslBlock(p, p.VertexFunc.Block, p.VertexFunc.Block, 0, 0)...)
 			vslines = append(vslines, "}")
 		}
 	}
@@ -126,10 +126,10 @@ func Compile(p *shaderir.Program) (vertexShader, fragmentShader string) {
 			}
 		}
 
-		if len(p.FragmentFunc.Block.Stmts) > 0 {
+		if p.FragmentFunc.Block != nil && len(p.FragmentFunc.Block.Stmts) > 0 {
 			fslines = append(fslines, "")
 			fslines = append(fslines, "void main(void) {")
-			fslines = append(fslines, c.glslBlock(p, &p.FragmentFunc.Block, &p.FragmentFunc.Block, 0, 0)...)
+			fslines = append(fslines, c.glslBlock(p, p.FragmentFunc.Block, p.FragmentFunc.Block, 0, 0)...)
 			fslines = append(fslines, "}")
 		}
 	}
@@ -239,7 +239,7 @@ func (c *compileContext) glslFunc(p *shaderir.Program, f *shaderir.Func, prototy
 		return lines
 	}
 	lines = append(lines, fmt.Sprintf("%s {", sig))
-	lines = append(lines, c.glslBlock(p, &f.Block, &f.Block, 0, idx)...)
+	lines = append(lines, c.glslBlock(p, f.Block, f.Block, 0, idx)...)
 	lines = append(lines, "}")
 
 	return lines
@@ -275,7 +275,7 @@ func constantToNumberLiteral(t shaderir.ConstType, v constant.Value) string {
 
 func localVariableName(p *shaderir.Program, topBlock *shaderir.Block, idx int) string {
 	switch topBlock {
-	case &p.VertexFunc.Block:
+	case p.VertexFunc.Block:
 		na := len(p.Attributes)
 		nv := len(p.Varyings)
 		switch {
@@ -288,7 +288,7 @@ func localVariableName(p *shaderir.Program, topBlock *shaderir.Block, idx int) s
 		default:
 			return fmt.Sprintf("l%d", idx-(na+nv+1))
 		}
-	case &p.FragmentFunc.Block:
+	case p.FragmentFunc.Block:
 		nv := len(p.Varyings)
 		switch {
 		case idx == 0:
@@ -306,6 +306,10 @@ func localVariableName(p *shaderir.Program, topBlock *shaderir.Block, idx int) s
 }
 
 func (c *compileContext) glslBlock(p *shaderir.Program, topBlock, block *shaderir.Block, level int, localVarIndex int) []string {
+	if block == nil {
+		return nil
+	}
+
 	idt := strings.Repeat("\t", level+1)
 
 	var lines []string
@@ -383,17 +387,17 @@ func (c *compileContext) glslBlock(p *shaderir.Program, topBlock, block *shaderi
 			lines = append(lines, fmt.Sprintf("%s%s;", idt, glslExpr(&s.Exprs[0])))
 		case shaderir.BlockStmt:
 			lines = append(lines, idt+"{")
-			lines = append(lines, c.glslBlock(p, topBlock, &s.Blocks[0], level+1, localVarIndex)...)
+			lines = append(lines, c.glslBlock(p, topBlock, s.Blocks[0], level+1, localVarIndex)...)
 			lines = append(lines, idt+"}")
 		case shaderir.Assign:
 			// TODO: Give an appropriate context
 			lines = append(lines, fmt.Sprintf("%s%s = %s;", idt, glslExpr(&s.Exprs[0]), glslExpr(&s.Exprs[1])))
 		case shaderir.If:
 			lines = append(lines, fmt.Sprintf("%sif (%s) {", idt, glslExpr(&s.Exprs[0])))
-			lines = append(lines, c.glslBlock(p, topBlock, &s.Blocks[0], level+1, localVarIndex)...)
+			lines = append(lines, c.glslBlock(p, topBlock, s.Blocks[0], level+1, localVarIndex)...)
 			if len(s.Blocks) > 1 {
 				lines = append(lines, fmt.Sprintf("%s} else {", idt))
-				lines = append(lines, c.glslBlock(p, topBlock, &s.Blocks[1], level+1, localVarIndex)...)
+				lines = append(lines, c.glslBlock(p, topBlock, s.Blocks[1], level+1, localVarIndex)...)
 			}
 			lines = append(lines, fmt.Sprintf("%s}", idt))
 		case shaderir.For:
@@ -436,7 +440,7 @@ func (c *compileContext) glslBlock(p *shaderir.Program, topBlock, block *shaderi
 			end := constantToNumberLiteral(ct, s.ForEnd)
 			t0, t1 := typeString(&t)
 			lines = append(lines, fmt.Sprintf("%sfor (%s %s%s = %s; %s %s %s; %s) {", idt, t0, v, t1, init, v, op, end, delta))
-			lines = append(lines, c.glslBlock(p, topBlock, &s.Blocks[0], level+1, localVarIndex)...)
+			lines = append(lines, c.glslBlock(p, topBlock, s.Blocks[0], level+1, localVarIndex)...)
 			lines = append(lines, fmt.Sprintf("%s}", idt))
 		case shaderir.Continue:
 			lines = append(lines, idt+"continue;")
diff --git a/internal/shaderir/ir_test.go b/internal/shaderir/ir_test.go
index 896a583ec..765c7b313 100644
--- a/internal/shaderir/ir_test.go
+++ b/internal/shaderir/ir_test.go
@@ -20,10 +20,11 @@ import (
 
 	. "github.com/hajimehoshi/ebiten/internal/shaderir"
 	"github.com/hajimehoshi/ebiten/internal/shaderir/glsl"
+	"github.com/hajimehoshi/ebiten/internal/shaderir/metal"
 )
 
-func block(localVars []Type, stmts ...Stmt) Block {
-	return Block{
+func block(localVars []Type, stmts ...Stmt) *Block {
+	return &Block{
 		LocalVars: localVars,
 		Stmts:     stmts,
 	}
@@ -36,10 +37,10 @@ func exprStmt(expr Expr) Stmt {
 	}
 }
 
-func blockStmt(block Block) Stmt {
+func blockStmt(block *Block) Stmt {
 	return Stmt{
 		Type:   BlockStmt,
-		Blocks: []Block{block},
+		Blocks: []*Block{block},
 	}
 }
 
@@ -57,18 +58,18 @@ func assignStmt(lhs Expr, rhs Expr) Stmt {
 	}
 }
 
-func ifStmt(cond Expr, block Block, elseBlock Block) Stmt {
+func ifStmt(cond Expr, block *Block, elseBlock *Block) Stmt {
 	return Stmt{
 		Type:   If,
 		Exprs:  []Expr{cond},
-		Blocks: []Block{block, elseBlock},
+		Blocks: []*Block{block, elseBlock},
 	}
 }
 
-func forStmt(index, init, end int, op Op, delta int, block Block) Stmt {
+func forStmt(index, init, end int, op Op, delta int, block *Block) Stmt {
 	return Stmt{
 		Type:        For,
-		Blocks:      []Block{block},
+		Blocks:      []*Block{block},
 		ForVarType:  Type{Main: Int},
 		ForVarIndex: index,
 		ForInit:     constant.MakeInt64(int64(init)),
@@ -837,6 +838,7 @@ void main(void) {
 					t.Errorf("%s fragment: got: %s, want: %s", tc.Name, got, want)
 				}
 			}
+			metal.Compile(&tc.Program, "Vertex", "Fragment")
 		})
 	}
 }
diff --git a/internal/shaderir/metal/metal.go b/internal/shaderir/metal/metal.go
index 53e765dba..58677787d 100644
--- a/internal/shaderir/metal/metal.go
+++ b/internal/shaderir/metal/metal.go
@@ -95,7 +95,7 @@ func Compile(p *shaderir.Program, vertex, fragment string) (shader string) {
 		}
 	}
 
-	if len(p.VertexFunc.Block.Stmts) > 0 {
+	if p.VertexFunc.Block != nil && len(p.VertexFunc.Block.Stmts) > 0 {
 		lines = append(lines, "")
 		lines = append(lines,
 			fmt.Sprintf("vertex Varyings %s(", vertex),
@@ -111,14 +111,14 @@ func Compile(p *shaderir.Program, vertex, fragment string) (shader string) {
 		}
 		lines[len(lines)-1] += ") {"
 		lines = append(lines, fmt.Sprintf("\tVaryings %s = {};", vertexOut))
-		lines = append(lines, c.metalBlock(p, &p.VertexFunc.Block, &p.VertexFunc.Block, 0, 0)...)
+		lines = append(lines, c.metalBlock(p, p.VertexFunc.Block, p.VertexFunc.Block, 0, 0)...)
 		if last := fmt.Sprintf("\treturn %s;", vertexOut); lines[len(lines)-1] != last {
 			lines = append(lines, last)
 		}
 		lines = append(lines, "}")
 	}
 
-	if len(p.FragmentFunc.Block.Stmts) > 0 {
+	if p.FragmentFunc.Block != nil && len(p.FragmentFunc.Block.Stmts) > 0 {
 		lines = append(lines, "")
 		lines = append(lines,
 			fmt.Sprintf("fragment float4 %s(", fragment),
@@ -133,7 +133,7 @@ func Compile(p *shaderir.Program, vertex, fragment string) (shader string) {
 		}
 		lines[len(lines)-1] += ") {"
 		lines = append(lines, fmt.Sprintf("\tfloat4 %s = float4(0);", fragmentOut))
-		lines = append(lines, c.metalBlock(p, &p.FragmentFunc.Block, &p.FragmentFunc.Block, 0, 0)...)
+		lines = append(lines, c.metalBlock(p, p.FragmentFunc.Block, p.FragmentFunc.Block, 0, 0)...)
 		if last := fmt.Sprintf("\treturn %s;", fragmentOut); lines[len(lines)-1] != last {
 			lines = append(lines, last)
 		}
@@ -245,7 +245,7 @@ func (c *compileContext) metalFunc(p *shaderir.Program, f *shaderir.Func, protot
 		return lines
 	}
 	lines = append(lines, fmt.Sprintf("%s {", sig))
-	lines = append(lines, c.metalBlock(p, &f.Block, &f.Block, 0, idx)...)
+	lines = append(lines, c.metalBlock(p, f.Block, f.Block, 0, idx)...)
 	lines = append(lines, "}")
 
 	return lines
@@ -281,7 +281,7 @@ func constantToNumberLiteral(t shaderir.ConstType, v constant.Value) string {
 
 func localVariableName(p *shaderir.Program, topBlock *shaderir.Block, idx int) string {
 	switch topBlock {
-	case &p.VertexFunc.Block:
+	case p.VertexFunc.Block:
 		na := len(p.Attributes)
 		nv := len(p.Varyings)
 		switch {
@@ -294,7 +294,7 @@ func localVariableName(p *shaderir.Program, topBlock *shaderir.Block, idx int) s
 		default:
 			return fmt.Sprintf("l%d", idx-(na+nv+1))
 		}
-	case &p.FragmentFunc.Block:
+	case p.FragmentFunc.Block:
 		nv := len(p.Varyings)
 		switch {
 		case idx == 0:
@@ -312,6 +312,10 @@ func localVariableName(p *shaderir.Program, topBlock *shaderir.Block, idx int) s
 }
 
 func (c *compileContext) metalBlock(p *shaderir.Program, topBlock, block *shaderir.Block, level int, localVarIndex int) []string {
+	if block == nil {
+		return nil
+	}
+
 	idt := strings.Repeat("\t", level+1)
 
 	var lines []string
@@ -391,17 +395,17 @@ func (c *compileContext) metalBlock(p *shaderir.Program, topBlock, block *shader
 			lines = append(lines, fmt.Sprintf("%s%s;", idt, metalExpr(&s.Exprs[0])))
 		case shaderir.BlockStmt:
 			lines = append(lines, idt+"{")
-			lines = append(lines, c.metalBlock(p, topBlock, &s.Blocks[0], level+1, localVarIndex)...)
+			lines = append(lines, c.metalBlock(p, topBlock, s.Blocks[0], level+1, localVarIndex)...)
 			lines = append(lines, idt+"}")
 		case shaderir.Assign:
 			// TODO: Give an appropriate context
 			lines = append(lines, fmt.Sprintf("%s%s = %s;", idt, metalExpr(&s.Exprs[0]), metalExpr(&s.Exprs[1])))
 		case shaderir.If:
 			lines = append(lines, fmt.Sprintf("%sif (%s) {", idt, metalExpr(&s.Exprs[0])))
-			lines = append(lines, c.metalBlock(p, topBlock, &s.Blocks[0], level+1, localVarIndex)...)
+			lines = append(lines, c.metalBlock(p, topBlock, s.Blocks[0], level+1, localVarIndex)...)
 			if len(s.Blocks) > 1 {
 				lines = append(lines, fmt.Sprintf("%s} else {", idt))
-				lines = append(lines, c.metalBlock(p, topBlock, &s.Blocks[1], level+1, localVarIndex)...)
+				lines = append(lines, c.metalBlock(p, topBlock, s.Blocks[1], level+1, localVarIndex)...)
 			}
 			lines = append(lines, fmt.Sprintf("%s}", idt))
 		case shaderir.For:
@@ -444,7 +448,7 @@ func (c *compileContext) metalBlock(p *shaderir.Program, topBlock, block *shader
 			end := constantToNumberLiteral(ct, s.ForEnd)
 			ts := typeString(&t, false, false)
 			lines = append(lines, fmt.Sprintf("%sfor (%s %s = %s; %s %s %s; %s) {", idt, ts, v, init, v, op, end, delta))
-			lines = append(lines, c.metalBlock(p, topBlock, &s.Blocks[0], level+1, localVarIndex)...)
+			lines = append(lines, c.metalBlock(p, topBlock, s.Blocks[0], level+1, localVarIndex)...)
 			lines = append(lines, fmt.Sprintf("%s}", idt))
 		case shaderir.Continue:
 			lines = append(lines, idt+"continue;")
@@ -452,9 +456,9 @@ func (c *compileContext) metalBlock(p *shaderir.Program, topBlock, block *shader
 			lines = append(lines, idt+"break;")
 		case shaderir.Return:
 			switch {
-			case topBlock == &p.VertexFunc.Block:
+			case topBlock == p.VertexFunc.Block:
 				lines = append(lines, fmt.Sprintf("%sreturn %s;", idt, vertexOut))
-			case topBlock == &p.FragmentFunc.Block:
+			case topBlock == p.FragmentFunc.Block:
 				lines = append(lines, fmt.Sprintf("%sreturn %s;", idt, fragmentOut))
 			case len(s.Exprs) == 0:
 				lines = append(lines, idt+"return;")
diff --git a/internal/shaderir/program.go b/internal/shaderir/program.go
index fe1566cfa..b5b2d0c28 100644
--- a/internal/shaderir/program.go
+++ b/internal/shaderir/program.go
@@ -36,7 +36,7 @@ type Func struct {
 	InParams  []Type
 	OutParams []Type
 	Return    Type
-	Block     Block
+	Block     *Block
 }
 
 // VertexFunc takes pseudo params, and the number if len(attributes) + len(varyings) + 1.
@@ -45,7 +45,7 @@ type Func struct {
 // If len(attributes) + 1 <= index < len(attributes) + len(varyings) + 1, the params are out-params and represent
 // varying variables.
 type VertexFunc struct {
-	Block Block
+	Block *Block
 }
 
 // FragmentFunc takes pseudo params, and the number is len(varyings) + 2.
@@ -53,7 +53,7 @@ type VertexFunc struct {
 // If index == len(varyings), the param represents (index-1)th verying variable.
 // If index == len(varyings)+1, the param is an out-param representing the color of the pixel (gl_FragColor in GLSL).
 type FragmentFunc struct {
-	Block Block
+	Block *Block
 }
 
 type Block struct {
@@ -64,7 +64,7 @@ type Block struct {
 type Stmt struct {
 	Type        StmtType
 	Exprs       []Expr
-	Blocks      []Block
+	Blocks      []*Block
 	ForVarType  Type
 	ForVarIndex int
 	ForInit     constant.Value
diff --git a/internal/testing/shader.go b/internal/testing/shader.go
index 5272283d5..8eea05663 100644
--- a/internal/testing/shader.go
+++ b/internal/testing/shader.go
@@ -173,7 +173,7 @@ var (
 		},
 	}
 	defaultVertexFunc = shaderir.VertexFunc{
-		Block: shaderir.Block{
+		Block: &shaderir.Block{
 			Stmts: []shaderir.Stmt{
 				{
 					Type: shaderir.Assign,
@@ -279,7 +279,7 @@ func ShaderProgramFill(r, g, b, a byte) shaderir.Program {
 
 	p := defaultProgram()
 	p.FragmentFunc = shaderir.FragmentFunc{
-		Block: shaderir.Block{
+		Block: &shaderir.Block{
 			Stmts: []shaderir.Stmt{
 				{
 					Type: shaderir.Assign,
@@ -413,7 +413,7 @@ func ShaderProgramImages(imageNum int) shaderir.Program {
 	})
 
 	p.FragmentFunc = shaderir.FragmentFunc{
-		Block: shaderir.Block{
+		Block: &shaderir.Block{
 			LocalVars: []shaderir.Type{
 				{Main: shaderir.Vec4},
 			},