物聯網是一個基於網際網路，讓能夠被獨立定址的設備實現互聯的網路，不再只是人對人或人對物品的溝通。
許多物聯網設備具有微控制器，在此論文中，此微控制器有以下特點：一、類精簡指令集，有16及32位元的指令。二、有16個16位元的暫存器。三、有兩種不同的硬體架構，分別擁有64個字節的數據記憶體和4096字節程序記憶體。

根據這些特點，尤其是記憶體有限的形況下，我們的目標讓此編譯器編譯出的程式碼能盡量減少。
為了實現這目標，我們專注於幾個問題。
一、暫存器的分配。
二、移植除法運算。
三、左和右移運算的設計。

我們使用 GCC 來當作為我們移植的編譯器系統。
在我們的實驗中，可以顯示兩種微控制器不同的代碼大小。
以及和愛特梅爾 (Atmel) AVR比較，顯示我們所使用的 Code Size 較小。

IoT refers to Internet of Things. It represents an evolution in which objects are ability to interacting with other objects and without requiring human-to-human or human-to-machine interaction. Each IoT device has the microcontroller. The microcontroller plays an important in the whole device. In this work, our architectures have the following feature:
1. RISC-like and with 16-bit and 32-bit instructions.
2. With 16 general purpose registers and each of them is 16-bit. All of the registers can separate to 8-bit and totally has 32 8-bit registers.
3. With two type of architectures, one is OTP-based and the other is SRAM-based.
4. OTP-based with 64 bytes data memory and 4096 bytes program memory.
5. SRAM-based with 1024 bytes data memory and 8192 words program memory.

According to these features, especially the little program memory size, we pay attention to compiler for IoT microcontrollers with code size reduction in this work.
To achieve this goal, we focus on several issue.
First, we give an alternative way to register allocation without temporary register. Second, the divide operation need to be porting. Third, the shift operation need to be arrangement concisely.

We use GNU Compiler Collection (GCC) for the environment of code generation.

In our experiment, we show the code size of both OTP-based and SRAM-based microcontroller in different optimization options. We compare our targets' code size to Atmel AVR and shows the result has reduced in average.

Abstract i
Contents iii
List of Figures v
List of Tables vi
1 Introduction 1
1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Overview of the Thesis . . . . . . . . . . . . . . . . . . . . . . 2
2 Background 4
2.1 Overview of Compiler System . . . . . . . . . . . . . . . . . . 4
2.2 The GNU Compiler Collection . . . . . . . . . . . . . . . . . . 5
2.2.1 The Components for GCC . . . . . . . . . . . . . . . . 6
2.2.2 The Main Compiler(cc1) . . . . . . . . . . . . . . . . . 7
2.3 Porting Mechanism of GCC . . . . . . . . . . . . . . . . . . . 10
2.3.1 Instruction Patterns - target.md . . . . . . . . . . . . . 11
2.3.2 Target Macros - target.h, target.c . . . . . . . . . . . . 11
3 Issue of Porting IoT Microcontrollers 15
3.1 IoT Microcontroller Features . . . . . . . . . . . . . . . . . . . 15
3.1.1 Registers . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.1.2 OTP-based and SRAM-based Architecture . . . . . . . 16
3.2 The Porting Issues of IoT Microcontrollers . . . . . . . . . . . 17
3.2.1 Registers Usage . . . . . . . . . . . . . . . . . . . . . . 17
3.2.2 Libgcc of divide operation . . . . . . . . . . . . . . . . 18
3.2.3 The shiht operation . . . . . . . . . . . . . . . . . . . . 18
4 Experiment Results 24
4.1 Benchmark . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
4.2 Experimental Results . . . . . . . . . . . . . . . . . . . . . . . 25
5 Conclusion 28
5.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
5.2 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

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