Implemented dead code elimination

src/build/Result.go

@@ -8,7 +8,8 @@ import (
 
 // Result contains all the compiled functions in a build.
 type Result struct {
-	Functions        map[string]*Function
+	Used             []*Function
+	Unused           map[string]*Function
 	instructionCount int
 }
 
@@ -27,13 +28,8 @@ func (r Result) Finalize() ([]byte, []byte) {
 	final.RegisterNumber(asm.MOVE, x64.SyscallRegisters[1], 0)
 	final.Syscall()
 
-	// Place the `main` function immediately after the entry point.
-	main := r.Functions["main"]
-	delete(r.Functions, "main")
-	final.Merge(&main.Assembler)
-
-	// Merge all the remaining functions.
-	for _, f := range r.Functions {
+	// Merge all the called functions.
+	for _, f := range r.Used {
 		final.Merge(&f.Assembler)
 	}