Implemented a basic optimization

src/build/asm/Instructions.go

@@ -15,6 +15,10 @@ func (a *Assembler) RegisterNumber(mnemonic Mnemonic, reg cpu.Register, number i
 
 // RegisterRegister adds an instruction using two registers.
 func (a *Assembler) RegisterRegister(mnemonic Mnemonic, left cpu.Register, right cpu.Register) {
+	if a.unnecessary(mnemonic, left, right) {
+		return
+	}
+
 	a.Instructions = append(a.Instructions, Instruction{
 		Mnemonic: mnemonic,
 		Data: &RegisterRegister{