diff --git a/internal/shaderir/glsl/glsl.go b/internal/shaderir/glsl/glsl.go
index 18b148615..d1c4deb59 100644
--- a/internal/shaderir/glsl/glsl.go
+++ b/internal/shaderir/glsl/glsl.go
@@ -19,7 +19,6 @@ import (
 	"go/constant"
 	"go/token"
 	"regexp"
-	"sort"
 	"strings"
 
 	"github.com/hajimehoshi/ebiten/v2/internal/shaderir"
@@ -99,12 +98,6 @@ func Compile(p *shaderir.Program, version GLSLVersion) (vertexShader, fragmentSh
 		structNames: map[string]string{},
 	}
 
-	indexToFunc := map[int]*shaderir.Func{}
-	for _, f := range p.Funcs {
-		f := f
-		indexToFunc[f.Index] = &f
-	}
-
 	// Vertex func
 	var vslines []string
 	{
@@ -136,12 +129,7 @@ func Compile(p *shaderir.Program, version GLSLVersion) (vertexShader, fragmentSh
 
 		var funcs []*shaderir.Func
 		if p.VertexFunc.Block != nil {
-			indices := p.ReachableFuncIndicesFromVertexShader()
-			sort.Ints(indices)
-			funcs = make([]*shaderir.Func, 0, len(indices))
-			for _, idx := range indices {
-				funcs = append(funcs, indexToFunc[idx])
-			}
+			funcs = p.ReachableFuncsFromVertexShader()
 		} else {
 			// When a vertex entry point is not defined, allow to put all the functions. This is useful for testing.
 			funcs = make([]*shaderir.Func, 0, len(p.Funcs))
@@ -234,12 +222,7 @@ func Compile(p *shaderir.Program, version GLSLVersion) (vertexShader, fragmentSh
 
 		var funcs []*shaderir.Func
 		if p.VertexFunc.Block != nil {
-			indices := p.ReachableFuncIndicesFromFragmentShader()
-			sort.Ints(indices)
-			funcs = make([]*shaderir.Func, 0, len(indices))
-			for _, idx := range indices {
-				funcs = append(funcs, indexToFunc[idx])
-			}
+			funcs = p.ReachableFuncsFromFragmentShader()
 		} else {
 			// When a fragment entry point is not defined, allow to put all the functions. This is useful for testing.
 			funcs = make([]*shaderir.Func, 0, len(p.Funcs))
diff --git a/internal/shaderir/program.go b/internal/shaderir/program.go
index b0745a2f2..7ca989f13 100644
--- a/internal/shaderir/program.go
+++ b/internal/shaderir/program.go
@@ -18,6 +18,7 @@ package shaderir
 import (
 	"go/constant"
 	"go/token"
+	"sort"
 	"strings"
 )
 
@@ -363,22 +364,28 @@ func IsValidSwizzling(s string) bool {
 	return false
 }
 
-func (p *Program) ReachableFuncIndicesFromVertexShader() []int {
-	return p.reachableFuncIndicesFromBlockEntryPoint(p.VertexFunc.Block)
+func (p *Program) ReachableFuncsFromVertexShader() []*Func {
+	return p.reachableFuncsFromBlockEntryPoint(p.VertexFunc.Block)
 }
 
-func (p *Program) ReachableFuncIndicesFromFragmentShader() []int {
-	return p.reachableFuncIndicesFromBlockEntryPoint(p.FragmentFunc.Block)
+func (p *Program) ReachableFuncsFromFragmentShader() []*Func {
+	return p.reachableFuncsFromBlockEntryPoint(p.FragmentFunc.Block)
 }
 
-func (p *Program) reachableFuncIndicesFromBlockEntryPoint(b *Block) []int {
+func (p *Program) reachableFuncsFromBlockEntryPoint(b *Block) []*Func {
 	indexToFunc := map[int]*Func{}
 	for _, f := range p.Funcs {
 		f := f
 		indexToFunc[f.Index] = &f
 	}
 	visited := map[int]struct{}{}
-	return reachableFuncIndicesFromBlock(b, indexToFunc, visited)
+	indices := reachableFuncIndicesFromBlock(b, indexToFunc, visited)
+	sort.Ints(indices)
+	funcs := make([]*Func, 0, len(indices))
+	for _, i := range indices {
+		funcs = append(funcs, indexToFunc[i])
+	}
+	return funcs
 }
 
 func reachableFuncIndicesFromBlock(b *Block, indexToFunc map[int]*Func, visited map[int]struct{}) []int {