# Assignment2: GNU Toolchain
contributed by < [TRChen11011](https://github.com/TRChen11011/GNU-Toolchain) >

## Install VMware and Ubuntu
I use ==Unbuntu Linux 22.04== on VMware
Because using clz to implement multification is cool.
## Instr
* Setting the environment var
> cd $HOME
> source riscv-none-elf-gcc/setenv
* make
> make
* Run code
> build/rv32emu test.elf
* Display the assembler mnemonics for the machine instructions and store to .txt file
> riscv-none-elf-objdump -d test > test.txt
* Check elf size
> riscv-none-elf-size ./test
## Before we modify the code
we use perfcount to implement CSR.
CSR is use to count the cycle of the code.

**perfcount/main.c**

#include <stdint.h>
#include <stdio.h>
#include <string.h>
//those are functions in the same dir in perfcounter used to take CSR
extern uint64_t get_cycles();
extern uint64_t get_instret();

int main(void)
{
    /* measure cycles */
    uint64_t instret = get_instret();
    uint64_t oldcount = get_cycles();
    
    /* fill the C code you choose here, so you can get the CSR*/
    
    uint64_t cyclecount = get_cycles() - oldcount;

    printf("cycle count: %u\n", (unsigned int) cyclecount);
    printf("instret: %x\n", (unsigned) (instret & 0xffffffff));
    return 0;
}

And we have to modify Makefile

.PHONY: clean

include ../../mk/toolchain.mk
    
/*-Ofast , -O1 , -O2 ... you want need to chane in Makefile*/
CFLAGS = -march=rv32i_zicsr_zifencei -mabi=ilp32 -O1 -Wall

OBJS = \
    /*if you want add file, fill in*/
    getcycles.o \
    getinstret.o \
    main.o
BIN = perfcount.elf /*the final result you generate*/

%.o: %.S
	$(CROSS_COMPILE)gcc $(CFLAGS) -c -o $@ $<

%.o: %.c
	$(CROSS_COMPILE)gcc $(CFLAGS) -c -o $@ $<

all: $(BIN)

$(BIN): $(OBJS)
	 $(CROSS_COMPILE)gcc -o $@ $^

clean:
	$(RM) $(BIN) $(OBJS)

## Choosen Project
I choose the project form < [陳彥佑](https://hackmd.io/ZlqmPMmHQieGU7-esbziRw?both) >

The project is to use clz to implement a 32bits * 32bits multiplier.
### C code after modify to CSR

#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include <inttypes.h>

extern uint64_t get_cycles();
extern uint64_t get_instret();

uint16_t CLZ_32(uint32_t x)
{
    x |= (x >> 1);
    x |= (x >> 2);
    x |= (x >> 4);
    x |= (x >> 8);
    x |= (x >> 16);

    x -= ((x >> 1) & 0x55555555);
    x = ((x >> 2) & 0x33333333) + (x & 0x33333333);
    x = ((x >> 4) + x) & 0x0f0f0f0f;
    x += (x >> 8);
    x += (x >> 16);

    return (32 - (x & 0x3f));
}

uint64_t efficient_int_mul(uint32_t A, uint32_t B) {
	
    uint16_t n = CLZ_32(A);
    uint16_t m = CLZ_32(B);
    uint16_t result_bits;
    if(n>m) 
	    result_bits = n;
    else{
	    result_bits = m; 
	    uint32_t temp = A;
	    A = B;
	    B = temp;
	}
		
    uint64_t result = 0;

    for (int i = 0; i < 32-result_bits; i++) {
        if ((A >> i) & 1) {
            result += ((uint64_t)B << i);
        }
    }

    return result;
}

int main(void)
{
    unsigned int state[WORDS] = {0};

    /* measure cycles */
    uint64_t instret = get_instret();
    uint64_t oldcount = get_cycles();
    
    uint32_t A = 0x12345678; 
    uint32_t B = 0xffffdddd;

    uint64_t result = efficient_int_mul(A, B);
    
    uint64_t cyclecount = get_cycles() - oldcount;

    printf("cycle count: %u\n", (unsigned int) cyclecount);
    printf("instret: %x\n", (unsigned) (instret & 0xffffffff));
    printf("uint64: %"PRIX64"\n", result);

    return 0;
}

## Assembly code
### -O1 Assembly code

0001016c <CLZ_32>:
   1016c:	00155793          	srl	a5,a0,0x1
   10170:	00a7e533          	or	a0,a5,a0
   10174:	00255793          	srl	a5,a0,0x2
   10178:	00a7e7b3          	or	a5,a5,a0
   1017c:	0047d513          	srl	a0,a5,0x4
   10180:	00f56533          	or	a0,a0,a5
   10184:	00855713          	srl	a4,a0,0x8
   10188:	00a76733          	or	a4,a4,a0
   1018c:	01075793          	srl	a5,a4,0x10
   10190:	00e7e7b3          	or	a5,a5,a4
   10194:	0017d713          	srl	a4,a5,0x1
   10198:	555556b7          	lui	a3,0x55555
   1019c:	55568693          	add	a3,a3,1365 # 55555555 <__BSS_END__+0x55537805>
   101a0:	00d77733          	and	a4,a4,a3
   101a4:	40e787b3          	sub	a5,a5,a4
   101a8:	0027d713          	srl	a4,a5,0x2
   101ac:	333336b7          	lui	a3,0x33333
   101b0:	33368693          	add	a3,a3,819 # 33333333 <__BSS_END__+0x333155e3>
   101b4:	00d77733          	and	a4,a4,a3
   101b8:	00d7f7b3          	and	a5,a5,a3
   101bc:	00f70733          	add	a4,a4,a5
   101c0:	00475793          	srl	a5,a4,0x4
   101c4:	00e787b3          	add	a5,a5,a4
   101c8:	0f0f1737          	lui	a4,0xf0f1
   101cc:	f0f70713          	add	a4,a4,-241 # f0f0f0f <__BSS_END__+0xf0d31bf>
   101d0:	00e7f7b3          	and	a5,a5,a4
   101d4:	0087d713          	srl	a4,a5,0x8
   101d8:	00f70733          	add	a4,a4,a5
   101dc:	01075793          	srl	a5,a4,0x10
   101e0:	00e787b3          	add	a5,a5,a4
   101e4:	03f7f793          	and	a5,a5,63
   101e8:	02000513          	li	a0,32
   101ec:	40f50533          	sub	a0,a0,a5
   101f0:	01051513          	sll	a0,a0,0x10
   101f4:	01055513          	srl	a0,a0,0x10
   101f8:	00008067          	ret

000101fc <efficient_int_mul>:
   101fc:	ff010113          	add	sp,sp,-16
   10200:	00112623          	sw	ra,12(sp)
   10204:	00812423          	sw	s0,8(sp)
   10208:	00912223          	sw	s1,4(sp)
   1020c:	01212023          	sw	s2,0(sp)
   10210:	00050493          	mv	s1,a0
   10214:	00058413          	mv	s0,a1
   10218:	f55ff0ef          	jal	1016c <CLZ_32>
   1021c:	00050913          	mv	s2,a0
   10220:	00040513          	mv	a0,s0
   10224:	f49ff0ef          	jal	1016c <CLZ_32>
   10228:	01257a63          	bgeu	a0,s2,1023c <efficient_int_mul+0x40>
   1022c:	00090513          	mv	a0,s2
   10230:	00040793          	mv	a5,s0
   10234:	00048413          	mv	s0,s1
   10238:	00078493          	mv	s1,a5
   1023c:	02000613          	li	a2,32
   10240:	40a60633          	sub	a2,a2,a0
   10244:	06c05463          	blez	a2,102ac <efficient_int_mul+0xb0>
   10248:	00000793          	li	a5,0
   1024c:	00000513          	li	a0,0
   10250:	00000593          	li	a1,0
   10254:	0014de13          	srl	t3,s1,0x1
   10258:	01f00313          	li	t1,31
   1025c:	00000893          	li	a7,0
   10260:	02c0006f          	j	1028c <efficient_int_mul+0x90>
   10264:	40f30733          	sub	a4,t1,a5
   10268:	00ee5733          	srl	a4,t3,a4
   1026c:	00f496b3          	sll	a3,s1,a5
   10270:	00d506b3          	add	a3,a0,a3
   10274:	00a6b833          	sltu	a6,a3,a0
   10278:	00e585b3          	add	a1,a1,a4
   1027c:	00068513          	mv	a0,a3
   10280:	00b805b3          	add	a1,a6,a1
   10284:	00178793          	add	a5,a5,1
   10288:	02c78663          	beq	a5,a2,102b4 <efficient_int_mul+0xb8>
   1028c:	00f45733          	srl	a4,s0,a5
   10290:	00177713          	and	a4,a4,1
   10294:	fe0708e3          	beqz	a4,10284 <efficient_int_mul+0x88>
   10298:	fe078713          	add	a4,a5,-32
   1029c:	fc0744e3          	bltz	a4,10264 <efficient_int_mul+0x68>
   102a0:	00e49733          	sll	a4,s1,a4
   102a4:	00088693          	mv	a3,a7
   102a8:	fc9ff06f          	j	10270 <efficient_int_mul+0x74>
   102ac:	00000513          	li	a0,0
   102b0:	00000593          	li	a1,0
   102b4:	00c12083          	lw	ra,12(sp)
   102b8:	00812403          	lw	s0,8(sp)
   102bc:	00412483          	lw	s1,4(sp)
   102c0:	00012903          	lw	s2,0(sp)
   102c4:	01010113          	add	sp,sp,16
   102c8:	00008067          	ret

000102cc <main>:
   102cc:	fe010113          	add	sp,sp,-32
   102d0:	00112e23          	sw	ra,28(sp)
   102d4:	00812c23          	sw	s0,24(sp)
   102d8:	00912a23          	sw	s1,20(sp)
   102dc:	01212823          	sw	s2,16(sp)
   102e0:	01312623          	sw	s3,12(sp)
   102e4:	e75ff0ef          	jal	10158 <get_instret>
   102e8:	00050913          	mv	s2,a0
   102ec:	e59ff0ef          	jal	10144 <get_cycles>
   102f0:	00050993          	mv	s3,a0
   102f4:	ffffe5b7          	lui	a1,0xffffe
   102f8:	ddd58593          	add	a1,a1,-547 # ffffdddd <__BSS_END__+0xfffe008d>
   102fc:	12345537          	lui	a0,0x12345
   10300:	67850513          	add	a0,a0,1656 # 12345678 <__BSS_END__+0x12327928>
   10304:	ef9ff0ef          	jal	101fc <efficient_int_mul>
   10308:	00050493          	mv	s1,a0
   1030c:	00058413          	mv	s0,a1
   10310:	e35ff0ef          	jal	10144 <get_cycles>
   10314:	413505b3          	sub	a1,a0,s3
   10318:	0001c537          	lui	a0,0x1c
   1031c:	bf050513          	add	a0,a0,-1040 # 1bbf0 <__clzsi2+0x6e>
   10320:	424000ef          	jal	10744 <printf>
   10324:	00090593          	mv	a1,s2
   10328:	0001c537          	lui	a0,0x1c
   1032c:	c0450513          	add	a0,a0,-1020 # 1bc04 <__clzsi2+0x82>
   10330:	414000ef          	jal	10744 <printf>
   10334:	00048613          	mv	a2,s1
   10338:	00040693          	mv	a3,s0
   1033c:	0001c537          	lui	a0,0x1c
   10340:	c1450513          	add	a0,a0,-1004 # 1bc14 <__clzsi2+0x92>
   10344:	400000ef          	jal	10744 <printf>
   10348:	00000513          	li	a0,0
   1034c:	01c12083          	lw	ra,28(sp)
   10350:	01812403          	lw	s0,24(sp)
   10354:	01412483          	lw	s1,20(sp)
   10358:	01012903          	lw	s2,16(sp)
   1035c:	00c12983          	lw	s3,12(sp)
   10360:	02010113          	add	sp,sp,32
   10364:	00008067          	ret

#### elf size
#### execute

- observe
- Total cycle count : `393`
- Total instruction count : `2c7`
- Register use : `$ra, $sp, $a0~$a7, $s0~$s3, $t0,%t1`

### -O2 Assembly code

00010208 <CLZ_32>:
   10208:	00155793          	srl	a5,a0,0x1
   1020c:	00a7e533          	or	a0,a5,a0
   10210:	00255793          	srl	a5,a0,0x2
   10214:	00a7e7b3          	or	a5,a5,a0
   10218:	0047d513          	srl	a0,a5,0x4
   1021c:	00f56533          	or	a0,a0,a5
   10220:	00855713          	srl	a4,a0,0x8
   10224:	00a76733          	or	a4,a4,a0
   10228:	01075793          	srl	a5,a4,0x10
   1022c:	00e7e7b3          	or	a5,a5,a4
   10230:	555556b7          	lui	a3,0x55555
   10234:	0017d713          	srl	a4,a5,0x1
   10238:	55568693          	add	a3,a3,1365 # 55555555 <__BSS_END__+0x55537805>
   1023c:	00d77733          	and	a4,a4,a3
   10240:	40e787b3          	sub	a5,a5,a4
   10244:	333336b7          	lui	a3,0x33333
   10248:	33368693          	add	a3,a3,819 # 33333333 <__BSS_END__+0x333155e3>
   1024c:	0027d713          	srl	a4,a5,0x2
   10250:	00d77733          	and	a4,a4,a3
   10254:	00d7f7b3          	and	a5,a5,a3
   10258:	00f70733          	add	a4,a4,a5
   1025c:	00475793          	srl	a5,a4,0x4
   10260:	0f0f16b7          	lui	a3,0xf0f1
   10264:	00e787b3          	add	a5,a5,a4
   10268:	f0f68693          	add	a3,a3,-241 # f0f0f0f <__BSS_END__+0xf0d31bf>
   1026c:	00d7f7b3          	and	a5,a5,a3
   10270:	0087d713          	srl	a4,a5,0x8
   10274:	00f70733          	add	a4,a4,a5
   10278:	01075793          	srl	a5,a4,0x10
   1027c:	00e787b3          	add	a5,a5,a4
   10280:	03f7f793          	and	a5,a5,63
   10284:	02000513          	li	a0,32
   10288:	40f50533          	sub	a0,a0,a5
   1028c:	01051513          	sll	a0,a0,0x10
   10290:	01055513          	srl	a0,a0,0x10
   10294:	00008067          	ret

00010298 <efficient_int_mul>:
   10298:	ff010113          	add	sp,sp,-16
   1029c:	00812423          	sw	s0,8(sp)
   102a0:	00912223          	sw	s1,4(sp)
   102a4:	01212023          	sw	s2,0(sp)
   102a8:	00112623          	sw	ra,12(sp)
   102ac:	00058413          	mv	s0,a1
   102b0:	00050493          	mv	s1,a0
   102b4:	f55ff0ef          	jal	10208 <CLZ_32>
   102b8:	00050913          	mv	s2,a0
   102bc:	00040513          	mv	a0,s0
   102c0:	f49ff0ef          	jal	10208 <CLZ_32>
   102c4:	01257a63          	bgeu	a0,s2,102d8 <efficient_int_mul+0x40>
   102c8:	00040793          	mv	a5,s0
   102cc:	00090513          	mv	a0,s2
   102d0:	00048413          	mv	s0,s1
   102d4:	00078493          	mv	s1,a5
   102d8:	02000613          	li	a2,32
   102dc:	40a60633          	sub	a2,a2,a0
   102e0:	06c05263          	blez	a2,10344 <efficient_int_mul+0xac>
   102e4:	00000793          	li	a5,0
   102e8:	00000513          	li	a0,0
   102ec:	00000593          	li	a1,0
   102f0:	0014d313          	srl	t1,s1,0x1
   102f4:	01f00893          	li	a7,31
   102f8:	0280006f          	j	10320 <efficient_int_mul+0x88>
   102fc:	00d496b3          	sll	a3,s1,a3
   10300:	00000713          	li	a4,0
   10304:	00e50733          	add	a4,a0,a4
   10308:	00a73833          	sltu	a6,a4,a0
   1030c:	00d585b3          	add	a1,a1,a3
   10310:	00070513          	mv	a0,a4
   10314:	00b805b3          	add	a1,a6,a1
   10318:	00178793          	add	a5,a5,1
   1031c:	02f60863          	beq	a2,a5,1034c <efficient_int_mul+0xb4>
   10320:	00f45733          	srl	a4,s0,a5
   10324:	00177713          	and	a4,a4,1
   10328:	fe078693          	add	a3,a5,-32
   1032c:	fe0706e3          	beqz	a4,10318 <efficient_int_mul+0x80>
   10330:	40f88833          	sub	a6,a7,a5
   10334:	fc06d4e3          	bgez	a3,102fc <efficient_int_mul+0x64>
   10338:	00f49733          	sll	a4,s1,a5
   1033c:	010356b3          	srl	a3,t1,a6
   10340:	fc5ff06f          	j	10304 <efficient_int_mul+0x6c>
   10344:	00000513          	li	a0,0
   10348:	00000593          	li	a1,0
   1034c:	00c12083          	lw	ra,12(sp)
   10350:	00812403          	lw	s0,8(sp)
   10354:	00412483          	lw	s1,4(sp)
   10358:	00012903          	lw	s2,0(sp)
   1035c:	01010113          	add	sp,sp,16
   10360:	00008067          	ret
   
000100b0 <main>:
   100b0:	fe010113          	add	sp,sp,-32
   100b4:	00112e23          	sw	ra,28(sp)
   100b8:	00812c23          	sw	s0,24(sp)
   100bc:	00912a23          	sw	s1,20(sp)
   100c0:	01212823          	sw	s2,16(sp)
   100c4:	01312623          	sw	s3,12(sp)
   100c8:	12c000ef          	jal	101f4 <get_instret>
   100cc:	00050913          	mv	s2,a0
   100d0:	110000ef          	jal	101e0 <get_cycles>
   100d4:	00050993          	mv	s3,a0
   100d8:	ffffe5b7          	lui	a1,0xffffe
   100dc:	12345537          	lui	a0,0x12345
   100e0:	ddd58593          	add	a1,a1,-547 # ffffdddd <__BSS_END__+0xfffe008d>
   100e4:	67850513          	add	a0,a0,1656 # 12345678 <__BSS_END__+0x12327928>
   100e8:	1b0000ef          	jal	10298 <efficient_int_mul>
   100ec:	00050493          	mv	s1,a0
   100f0:	00058413          	mv	s0,a1
   100f4:	0ec000ef          	jal	101e0 <get_cycles>
   100f8:	413505b3          	sub	a1,a0,s3
   100fc:	0001c537          	lui	a0,0x1c
   10100:	bf050513          	add	a0,a0,-1040 # 1bbf0 <__clzsi2+0x72>
   10104:	63c000ef          	jal	10740 <printf>
   10108:	0001c537          	lui	a0,0x1c
   1010c:	00090593          	mv	a1,s2
   10110:	c0450513          	add	a0,a0,-1020 # 1bc04 <__clzsi2+0x86>
   10114:	62c000ef          	jal	10740 <printf>
   10118:	0001c537          	lui	a0,0x1c
   1011c:	00048613          	mv	a2,s1
   10120:	00040693          	mv	a3,s0
   10124:	c1450513          	add	a0,a0,-1004 # 1bc14 <__clzsi2+0x96>
   10128:	618000ef          	jal	10740 <printf>
   1012c:	01c12083          	lw	ra,28(sp)
   10130:	01812403          	lw	s0,24(sp)
   10134:	01412483          	lw	s1,20(sp)
   10138:	01012903          	lw	s2,16(sp)
   1013c:	00c12983          	lw	s3,12(sp)
   10140:	00000513          	li	a0,0
   10144:	02010113          	add	sp,sp,32
   10148:	00008067          	ret

#### elf size
#### execute

- observe
- Total cycle count : `421`
- Total instruction count : `2c7`
- Register use : `$ra, $sp, $a0~$a7, $s0~$s3, $t1`

### -O3 Assembly code

00010208 <CLZ_32>:
   10208:	00155793          	srl	a5,a0,0x1
   1020c:	00a7e533          	or	a0,a5,a0
   10210:	00255793          	srl	a5,a0,0x2
   10214:	00a7e7b3          	or	a5,a5,a0
   10218:	0047d513          	srl	a0,a5,0x4
   1021c:	00f56533          	or	a0,a0,a5
   10220:	00855713          	srl	a4,a0,0x8
   10224:	00a76733          	or	a4,a4,a0
   10228:	01075793          	srl	a5,a4,0x10
   1022c:	00e7e7b3          	or	a5,a5,a4
   10230:	555556b7          	lui	a3,0x55555
   10234:	0017d713          	srl	a4,a5,0x1
   10238:	55568693          	add	a3,a3,1365 # 55555555 <__BSS_END__+0x55537805>
   1023c:	00d77733          	and	a4,a4,a3
   10240:	40e787b3          	sub	a5,a5,a4
   10244:	333336b7          	lui	a3,0x33333
   10248:	33368693          	add	a3,a3,819 # 33333333 <__BSS_END__+0x333155e3>
   1024c:	0027d713          	srl	a4,a5,0x2
   10250:	00d77733          	and	a4,a4,a3
   10254:	00d7f7b3          	and	a5,a5,a3
   10258:	00f70733          	add	a4,a4,a5
   1025c:	00475793          	srl	a5,a4,0x4
   10260:	0f0f16b7          	lui	a3,0xf0f1
   10264:	00e787b3          	add	a5,a5,a4
   10268:	f0f68693          	add	a3,a3,-241 # f0f0f0f <__BSS_END__+0xf0d31bf>
   1026c:	00d7f7b3          	and	a5,a5,a3
   10270:	0087d713          	srl	a4,a5,0x8
   10274:	00f70733          	add	a4,a4,a5
   10278:	01075793          	srl	a5,a4,0x10
   1027c:	00e787b3          	add	a5,a5,a4
   10280:	03f7f793          	and	a5,a5,63
   10284:	02000513          	li	a0,32
   10288:	40f50533          	sub	a0,a0,a5
   1028c:	01051513          	sll	a0,a0,0x10
   10290:	01055513          	srl	a0,a0,0x10
   10294:	00008067          	ret

00010298 <efficient_int_mul>:
   10298:	00155713          	srl	a4,a0,0x1
   1029c:	0015d793          	srl	a5,a1,0x1
   102a0:	00a76733          	or	a4,a4,a0
   102a4:	00b7e7b3          	or	a5,a5,a1
   102a8:	0027d693          	srl	a3,a5,0x2
   102ac:	00058613          	mv	a2,a1
   102b0:	00275593          	srl	a1,a4,0x2
   102b4:	00b76733          	or	a4,a4,a1
   102b8:	00d7e7b3          	or	a5,a5,a3
   102bc:	00475593          	srl	a1,a4,0x4
   102c0:	0047d693          	srl	a3,a5,0x4
   102c4:	00b76733          	or	a4,a4,a1
   102c8:	00d7e7b3          	or	a5,a5,a3
   102cc:	00875593          	srl	a1,a4,0x8
   102d0:	0087d693          	srl	a3,a5,0x8
   102d4:	00b76733          	or	a4,a4,a1
   102d8:	00d7e7b3          	or	a5,a5,a3
   102dc:	01075593          	srl	a1,a4,0x10
   102e0:	0107d693          	srl	a3,a5,0x10
   102e4:	00b76733          	or	a4,a4,a1
   102e8:	00d7e7b3          	or	a5,a5,a3
   102ec:	555556b7          	lui	a3,0x55555
   102f0:	0017d593          	srl	a1,a5,0x1
   102f4:	55568693          	add	a3,a3,1365 # 55555555 <__BSS_END__+0x55537805>
   102f8:	00050813          	mv	a6,a0
   102fc:	00175513          	srl	a0,a4,0x1
   10300:	00d57533          	and	a0,a0,a3
   10304:	00d5f6b3          	and	a3,a1,a3
   10308:	40a70733          	sub	a4,a4,a0
   1030c:	40d787b3          	sub	a5,a5,a3
   10310:	33333537          	lui	a0,0x33333
   10314:	33350513          	add	a0,a0,819 # 33333333 <__BSS_END__+0x333155e3>
   10318:	00275593          	srl	a1,a4,0x2
   1031c:	0027d693          	srl	a3,a5,0x2
   10320:	00a77733          	and	a4,a4,a0
   10324:	00a7f7b3          	and	a5,a5,a0
   10328:	00a5f5b3          	and	a1,a1,a0
   1032c:	00a6f6b3          	and	a3,a3,a0
   10330:	00e585b3          	add	a1,a1,a4
   10334:	00f686b3          	add	a3,a3,a5
   10338:	0046d713          	srl	a4,a3,0x4
   1033c:	0045d793          	srl	a5,a1,0x4
   10340:	0f0f1537          	lui	a0,0xf0f1
   10344:	f0f50513          	add	a0,a0,-241 # f0f0f0f <__BSS_END__+0xf0d31bf>
   10348:	00b787b3          	add	a5,a5,a1
   1034c:	00d70733          	add	a4,a4,a3
   10350:	00a7f7b3          	and	a5,a5,a0
   10354:	00a77733          	and	a4,a4,a0
   10358:	0087d593          	srl	a1,a5,0x8
   1035c:	00875693          	srl	a3,a4,0x8
   10360:	00b787b3          	add	a5,a5,a1
   10364:	00d70733          	add	a4,a4,a3
   10368:	01075693          	srl	a3,a4,0x10
   1036c:	0107d593          	srl	a1,a5,0x10
   10370:	00d70733          	add	a4,a4,a3
   10374:	00b787b3          	add	a5,a5,a1
   10378:	02000693          	li	a3,32
   1037c:	03f7f793          	and	a5,a5,63
   10380:	03f77713          	and	a4,a4,63
   10384:	40f687b3          	sub	a5,a3,a5
   10388:	40e68733          	sub	a4,a3,a4
   1038c:	01079793          	sll	a5,a5,0x10
   10390:	01071713          	sll	a4,a4,0x10
   10394:	0107d793          	srl	a5,a5,0x10
   10398:	01075713          	srl	a4,a4,0x10
   1039c:	00f77a63          	bgeu	a4,a5,103b0 <efficient_int_mul+0x118>
   103a0:	00060693          	mv	a3,a2
   103a4:	00078713          	mv	a4,a5
   103a8:	00080613          	mv	a2,a6
   103ac:	00068813          	mv	a6,a3
   103b0:	02000893          	li	a7,32
   103b4:	40e888b3          	sub	a7,a7,a4
   103b8:	07105463          	blez	a7,10420 <efficient_int_mul+0x188>
   103bc:	00000793          	li	a5,0
   103c0:	00000513          	li	a0,0
   103c4:	00000593          	li	a1,0
   103c8:	00185e93          	srl	t4,a6,0x1
   103cc:	01f00e13          	li	t3,31
   103d0:	0280006f          	j	103f8 <efficient_int_mul+0x160>
   103d4:	00d816b3          	sll	a3,a6,a3
   103d8:	00000713          	li	a4,0
   103dc:	00e50733          	add	a4,a0,a4
   103e0:	00a73333          	sltu	t1,a4,a0
   103e4:	00d585b3          	add	a1,a1,a3
   103e8:	00070513          	mv	a0,a4
   103ec:	00b305b3          	add	a1,t1,a1
   103f0:	00178793          	add	a5,a5,1
   103f4:	02f88463          	beq	a7,a5,1041c <efficient_int_mul+0x184>
   103f8:	00f65733          	srl	a4,a2,a5
   103fc:	00177713          	and	a4,a4,1
   10400:	fe078693          	add	a3,a5,-32
   10404:	fe0706e3          	beqz	a4,103f0 <efficient_int_mul+0x158>
   10408:	40fe0333          	sub	t1,t3,a5
   1040c:	fc06d4e3          	bgez	a3,103d4 <efficient_int_mul+0x13c>
   10410:	00f81733          	sll	a4,a6,a5
   10414:	006ed6b3          	srl	a3,t4,t1
   10418:	fc5ff06f          	j	103dc <efficient_int_mul+0x144>
   1041c:	00008067          	ret
   10420:	00000513          	li	a0,0
   10424:	00000593          	li	a1,0
   10428:	00008067          	ret
   
000100b0 <main>:
   100b0:	fe010113          	add	sp,sp,-32
   100b4:	00112e23          	sw	ra,28(sp)
   100b8:	00812c23          	sw	s0,24(sp)
   100bc:	00912a23          	sw	s1,20(sp)
   100c0:	01212823          	sw	s2,16(sp)
   100c4:	01312623          	sw	s3,12(sp)
   100c8:	12c000ef          	jal	101f4 <get_instret>
   100cc:	00050913          	mv	s2,a0
   100d0:	110000ef          	jal	101e0 <get_cycles>
   100d4:	00050993          	mv	s3,a0
   100d8:	ffffe5b7          	lui	a1,0xffffe
   100dc:	12345537          	lui	a0,0x12345
   100e0:	ddd58593          	add	a1,a1,-547 # ffffdddd <__BSS_END__+0xfffe008d>
   100e4:	67850513          	add	a0,a0,1656 # 12345678 <__BSS_END__+0x12327928>
   100e8:	1b0000ef          	jal	10298 <efficient_int_mul>
   100ec:	00050493          	mv	s1,a0
   100f0:	00058413          	mv	s0,a1
   100f4:	0ec000ef          	jal	101e0 <get_cycles>
   100f8:	413505b3          	sub	a1,a0,s3
   100fc:	0001c537          	lui	a0,0x1c
   10100:	cb850513          	add	a0,a0,-840 # 1bcb8 <__clzsi2+0x72>
   10104:	704000ef          	jal	10808 <printf>
   10108:	0001c537          	lui	a0,0x1c
   1010c:	00090593          	mv	a1,s2
   10110:	ccc50513          	add	a0,a0,-820 # 1bccc <__clzsi2+0x86>
   10114:	6f4000ef          	jal	10808 <printf>
   10118:	0001c537          	lui	a0,0x1c
   1011c:	00048613          	mv	a2,s1
   10120:	00040693          	mv	a3,s0
   10124:	cdc50513          	add	a0,a0,-804 # 1bcdc <__clzsi2+0x96>
   10128:	6e0000ef          	jal	10808 <printf>
   1012c:	01c12083          	lw	ra,28(sp)
   10130:	01812403          	lw	s0,24(sp)
   10134:	01412483          	lw	s1,20(sp)
   10138:	01012903          	lw	s2,16(sp)
   1013c:	00c12983          	lw	s3,12(sp)
   10140:	00000513          	li	a0,0
   10144:	02010113          	add	sp,sp,32
   10148:	00008067          	ret

#### elf size

#### execute

- observe
- Total cycle count : `398`
- Total instruction count : `2c7`
- Register use : `$ra, $sp, $a0~$a7, $s0~$s3, $t1, $t3, $t4`

### -Os Assembly code

000101f8 <CLZ_32>:
   101f8:	00155793          	srl	a5,a0,0x1
   101fc:	00a7e533          	or	a0,a5,a0
   10200:	00255793          	srl	a5,a0,0x2
   10204:	00a7e7b3          	or	a5,a5,a0
   10208:	0047d513          	srl	a0,a5,0x4
   1020c:	00f56533          	or	a0,a0,a5
   10210:	00855713          	srl	a4,a0,0x8
   10214:	00a76733          	or	a4,a4,a0
   10218:	01075793          	srl	a5,a4,0x10
   1021c:	00e7e7b3          	or	a5,a5,a4
   10220:	555556b7          	lui	a3,0x55555
   10224:	0017d713          	srl	a4,a5,0x1
   10228:	55568693          	add	a3,a3,1365 # 55555555 <__BSS_END__+0x55537805>
   1022c:	00d77733          	and	a4,a4,a3
   10230:	40e787b3          	sub	a5,a5,a4
   10234:	333336b7          	lui	a3,0x33333
   10238:	33368693          	add	a3,a3,819 # 33333333 <__BSS_END__+0x333155e3>
   1023c:	0027d713          	srl	a4,a5,0x2
   10240:	00d77733          	and	a4,a4,a3
   10244:	00d7f7b3          	and	a5,a5,a3
   10248:	00f70733          	add	a4,a4,a5
   1024c:	00475793          	srl	a5,a4,0x4
   10250:	00e787b3          	add	a5,a5,a4
   10254:	0f0f1737          	lui	a4,0xf0f1
   10258:	f0f70713          	add	a4,a4,-241 # f0f0f0f <__BSS_END__+0xf0d31bf>
   1025c:	00e7f7b3          	and	a5,a5,a4
   10260:	0087d713          	srl	a4,a5,0x8
   10264:	00f70733          	add	a4,a4,a5
   10268:	01075793          	srl	a5,a4,0x10
   1026c:	00e787b3          	add	a5,a5,a4
   10270:	03f7f793          	and	a5,a5,63
   10274:	02000513          	li	a0,32
   10278:	40f50533          	sub	a0,a0,a5
   1027c:	01051513          	sll	a0,a0,0x10
   10280:	01055513          	srl	a0,a0,0x10
   10284:	00008067          	ret

00010288 <efficient_int_mul>:
   10288:	fe010113          	add	sp,sp,-32
   1028c:	00812c23          	sw	s0,24(sp)
   10290:	00912a23          	sw	s1,20(sp)
   10294:	01312623          	sw	s3,12(sp)
   10298:	00112e23          	sw	ra,28(sp)
   1029c:	01212823          	sw	s2,16(sp)
   102a0:	01412423          	sw	s4,8(sp)
   102a4:	01512223          	sw	s5,4(sp)
   102a8:	00058413          	mv	s0,a1
   102ac:	00050993          	mv	s3,a0
   102b0:	f49ff0ef          	jal	101f8 <CLZ_32>
   102b4:	00050493          	mv	s1,a0
   102b8:	00040513          	mv	a0,s0
   102bc:	f3dff0ef          	jal	101f8 <CLZ_32>
   102c0:	00957a63          	bgeu	a0,s1,102d4 <efficient_int_mul+0x4c>
   102c4:	00040793          	mv	a5,s0
   102c8:	00048513          	mv	a0,s1
   102cc:	00098413          	mv	s0,s3
   102d0:	00078993          	mv	s3,a5
   102d4:	02000a93          	li	s5,32
   102d8:	00000913          	li	s2,0
   102dc:	00000a13          	li	s4,0
   102e0:	00000493          	li	s1,0
   102e4:	40aa8ab3          	sub	s5,s5,a0
   102e8:	03594863          	blt	s2,s5,10318 <efficient_int_mul+0x90>
   102ec:	01c12083          	lw	ra,28(sp)
   102f0:	01812403          	lw	s0,24(sp)
   102f4:	01012903          	lw	s2,16(sp)
   102f8:	00c12983          	lw	s3,12(sp)
   102fc:	00412a83          	lw	s5,4(sp)
   10300:	000a0513          	mv	a0,s4
   10304:	00048593          	mv	a1,s1
   10308:	00812a03          	lw	s4,8(sp)
   1030c:	01412483          	lw	s1,20(sp)
   10310:	02010113          	add	sp,sp,32
   10314:	00008067          	ret
   10318:	012457b3          	srl	a5,s0,s2
   1031c:	0017f793          	and	a5,a5,1
   10320:	02078463          	beqz	a5,10348 <efficient_int_mul+0xc0>
   10324:	00090613          	mv	a2,s2
   10328:	00098513          	mv	a0,s3
   1032c:	00000593          	li	a1,0
   10330:	020000ef          	jal	10350 <__ashldi3>
   10334:	00aa0533          	add	a0,s4,a0
   10338:	014537b3          	sltu	a5,a0,s4
   1033c:	00b484b3          	add	s1,s1,a1
   10340:	00050a13          	mv	s4,a0
   10344:	009784b3          	add	s1,a5,s1
   10348:	00190913          	add	s2,s2,1
   1034c:	f9dff06f          	j	102e8 <efficient_int_mul+0x60>

000100b0 <main>:
   100b0:	fe010113          	add	sp,sp,-32
   100b4:	00112e23          	sw	ra,28(sp)
   100b8:	00812c23          	sw	s0,24(sp)
   100bc:	00912a23          	sw	s1,20(sp)
   100c0:	124000ef          	jal	101e4 <get_instret>
   100c4:	00050413          	mv	s0,a0
   100c8:	108000ef          	jal	101d0 <get_cycles>
   100cc:	00050493          	mv	s1,a0
   100d0:	ffffe5b7          	lui	a1,0xffffe
   100d4:	12345537          	lui	a0,0x12345
   100d8:	ddd58593          	add	a1,a1,-547 # ffffdddd <__BSS_END__+0xfffe008d>
   100dc:	67850513          	add	a0,a0,1656 # 12345678 <__BSS_END__+0x12327928>
   100e0:	1a8000ef          	jal	10288 <efficient_int_mul>
   100e4:	00a12623          	sw	a0,12(sp)
   100e8:	00b12423          	sw	a1,8(sp)
   100ec:	0e4000ef          	jal	101d0 <get_cycles>
   100f0:	409505b3          	sub	a1,a0,s1
   100f4:	0001c537          	lui	a0,0x1c
   100f8:	c0050513          	add	a0,a0,-1024 # 1bc00 <__clzsi2+0x70>
   100fc:	656000ef          	jal	10752 <printf>
   10100:	0001c537          	lui	a0,0x1c
   10104:	00040593          	mv	a1,s0
   10108:	c1450513          	add	a0,a0,-1004 # 1bc14 <__clzsi2+0x84>
   1010c:	646000ef          	jal	10752 <printf>
   10110:	00c12603          	lw	a2,12(sp)
   10114:	00812683          	lw	a3,8(sp)
   10118:	0001c537          	lui	a0,0x1c
   1011c:	c2450513          	add	a0,a0,-988 # 1bc24 <__clzsi2+0x94>
   10120:	632000ef          	jal	10752 <printf>
   10124:	01c12083          	lw	ra,28(sp)
   10128:	01812403          	lw	s0,24(sp)
   1012c:	01412483          	lw	s1,20(sp)
   10130:	00000513          	li	a0,0
   10134:	02010113          	add	sp,sp,32
   10138:	00008067          	ret

#### elf size

#### execute

- observe
- Total cycle count : `530`
- Total instruction count : `2c5`
- Register use : `$ra, $sp, $a0~$a7, $s0~$s3`

### -Ofast Assembly code

00010208 <CLZ_32>:
   10208:	00155793          	srl	a5,a0,0x1
   1020c:	00a7e533          	or	a0,a5,a0
   10210:	00255793          	srl	a5,a0,0x2
   10214:	00a7e7b3          	or	a5,a5,a0
   10218:	0047d513          	srl	a0,a5,0x4
   1021c:	00f56533          	or	a0,a0,a5
   10220:	00855713          	srl	a4,a0,0x8
   10224:	00a76733          	or	a4,a4,a0
   10228:	01075793          	srl	a5,a4,0x10
   1022c:	00e7e7b3          	or	a5,a5,a4
   10230:	555556b7          	lui	a3,0x55555
   10234:	0017d713          	srl	a4,a5,0x1
   10238:	55568693          	add	a3,a3,1365 # 55555555 <__BSS_END__+0x55537805>
   1023c:	00d77733          	and	a4,a4,a3
   10240:	40e787b3          	sub	a5,a5,a4
   10244:	333336b7          	lui	a3,0x33333
   10248:	33368693          	add	a3,a3,819 # 33333333 <__BSS_END__+0x333155e3>
   1024c:	0027d713          	srl	a4,a5,0x2
   10250:	00d77733          	and	a4,a4,a3
   10254:	00d7f7b3          	and	a5,a5,a3
   10258:	00f70733          	add	a4,a4,a5
   1025c:	00475793          	srl	a5,a4,0x4
   10260:	0f0f16b7          	lui	a3,0xf0f1
   10264:	00e787b3          	add	a5,a5,a4
   10268:	f0f68693          	add	a3,a3,-241 # f0f0f0f <__BSS_END__+0xf0d31bf>
   1026c:	00d7f7b3          	and	a5,a5,a3
   10270:	0087d713          	srl	a4,a5,0x8
   10274:	00f70733          	add	a4,a4,a5
   10278:	01075793          	srl	a5,a4,0x10
   1027c:	00e787b3          	add	a5,a5,a4
   10280:	03f7f793          	and	a5,a5,63
   10284:	02000513          	li	a0,32
   10288:	40f50533          	sub	a0,a0,a5
   1028c:	01051513          	sll	a0,a0,0x10
   10290:	01055513          	srl	a0,a0,0x10
   10294:	00008067          	ret

00010298 <efficient_int_mul>:
   10298:	00155713          	srl	a4,a0,0x1
   1029c:	0015d793          	srl	a5,a1,0x1
   102a0:	00a76733          	or	a4,a4,a0
   102a4:	00b7e7b3          	or	a5,a5,a1
   102a8:	0027d693          	srl	a3,a5,0x2
   102ac:	00058613          	mv	a2,a1
   102b0:	00275593          	srl	a1,a4,0x2
   102b4:	00b76733          	or	a4,a4,a1
   102b8:	00d7e7b3          	or	a5,a5,a3
   102bc:	00475593          	srl	a1,a4,0x4
   102c0:	0047d693          	srl	a3,a5,0x4
   102c4:	00b76733          	or	a4,a4,a1
   102c8:	00d7e7b3          	or	a5,a5,a3
   102cc:	00875593          	srl	a1,a4,0x8
   102d0:	0087d693          	srl	a3,a5,0x8
   102d4:	00b76733          	or	a4,a4,a1
   102d8:	00d7e7b3          	or	a5,a5,a3
   102dc:	01075593          	srl	a1,a4,0x10
   102e0:	0107d693          	srl	a3,a5,0x10
   102e4:	00b76733          	or	a4,a4,a1
   102e8:	00d7e7b3          	or	a5,a5,a3
   102ec:	555556b7          	lui	a3,0x55555
   102f0:	0017d593          	srl	a1,a5,0x1
   102f4:	55568693          	add	a3,a3,1365 # 55555555 <__BSS_END__+0x55537805>
   102f8:	00050813          	mv	a6,a0
   102fc:	00175513          	srl	a0,a4,0x1
   10300:	00d57533          	and	a0,a0,a3
   10304:	00d5f6b3          	and	a3,a1,a3
   10308:	40a70733          	sub	a4,a4,a0
   1030c:	40d787b3          	sub	a5,a5,a3
   10310:	33333537          	lui	a0,0x33333
   10314:	33350513          	add	a0,a0,819 # 33333333 <__BSS_END__+0x333155e3>
   10318:	00275593          	srl	a1,a4,0x2
   1031c:	0027d693          	srl	a3,a5,0x2
   10320:	00a77733          	and	a4,a4,a0
   10324:	00a7f7b3          	and	a5,a5,a0
   10328:	00a5f5b3          	and	a1,a1,a0
   1032c:	00a6f6b3          	and	a3,a3,a0
   10330:	00e585b3          	add	a1,a1,a4
   10334:	00f686b3          	add	a3,a3,a5
   10338:	0046d713          	srl	a4,a3,0x4
   1033c:	0045d793          	srl	a5,a1,0x4
   10340:	0f0f1537          	lui	a0,0xf0f1
   10344:	f0f50513          	add	a0,a0,-241 # f0f0f0f <__BSS_END__+0xf0d31bf>
   10348:	00b787b3          	add	a5,a5,a1
   1034c:	00d70733          	add	a4,a4,a3
   10350:	00a7f7b3          	and	a5,a5,a0
   10354:	00a77733          	and	a4,a4,a0
   10358:	0087d593          	srl	a1,a5,0x8
   1035c:	00875693          	srl	a3,a4,0x8
   10360:	00b787b3          	add	a5,a5,a1
   10364:	00d70733          	add	a4,a4,a3
   10368:	01075693          	srl	a3,a4,0x10
   1036c:	0107d593          	srl	a1,a5,0x10
   10370:	00d70733          	add	a4,a4,a3
   10374:	00b787b3          	add	a5,a5,a1
   10378:	02000693          	li	a3,32
   1037c:	03f7f793          	and	a5,a5,63
   10380:	03f77713          	and	a4,a4,63
   10384:	40f687b3          	sub	a5,a3,a5
   10388:	40e68733          	sub	a4,a3,a4
   1038c:	01079793          	sll	a5,a5,0x10
   10390:	01071713          	sll	a4,a4,0x10
   10394:	0107d793          	srl	a5,a5,0x10
   10398:	01075713          	srl	a4,a4,0x10
   1039c:	00f77a63          	bgeu	a4,a5,103b0 <efficient_int_mul+0x118>
   103a0:	00060693          	mv	a3,a2
   103a4:	00078713          	mv	a4,a5
   103a8:	00080613          	mv	a2,a6
   103ac:	00068813          	mv	a6,a3
   103b0:	02000893          	li	a7,32
   103b4:	40e888b3          	sub	a7,a7,a4
   103b8:	07105463          	blez	a7,10420 <efficient_int_mul+0x188>
   103bc:	00000793          	li	a5,0
   103c0:	00000513          	li	a0,0
   103c4:	00000593          	li	a1,0
   103c8:	00185e93          	srl	t4,a6,0x1
   103cc:	01f00e13          	li	t3,31
   103d0:	0280006f          	j	103f8 <efficient_int_mul+0x160>
   103d4:	00d816b3          	sll	a3,a6,a3
   103d8:	00000713          	li	a4,0
   103dc:	00e50733          	add	a4,a0,a4
   103e0:	00a73333          	sltu	t1,a4,a0
   103e4:	00d585b3          	add	a1,a1,a3
   103e8:	00070513          	mv	a0,a4
   103ec:	00b305b3          	add	a1,t1,a1
   103f0:	00178793          	add	a5,a5,1
   103f4:	02f88463          	beq	a7,a5,1041c <efficient_int_mul+0x184>
   103f8:	00f65733          	srl	a4,a2,a5
   103fc:	00177713          	and	a4,a4,1
   10400:	fe078693          	add	a3,a5,-32
   10404:	fe0706e3          	beqz	a4,103f0 <efficient_int_mul+0x158>
   10408:	40fe0333          	sub	t1,t3,a5
   1040c:	fc06d4e3          	bgez	a3,103d4 <efficient_int_mul+0x13c>
   10410:	00f81733          	sll	a4,a6,a5
   10414:	006ed6b3          	srl	a3,t4,t1
   10418:	fc5ff06f          	j	103dc <efficient_int_mul+0x144>
   1041c:	00008067          	ret
   10420:	00000513          	li	a0,0
   10424:	00000593          	li	a1,0
   10428:	00008067          	ret

000100b0 <main>:
   100b0:	fe010113          	add	sp,sp,-32
   100b4:	00112e23          	sw	ra,28(sp)
   100b8:	00812c23          	sw	s0,24(sp)
   100bc:	00912a23          	sw	s1,20(sp)
   100c0:	01212823          	sw	s2,16(sp)
   100c4:	01312623          	sw	s3,12(sp)
   100c8:	12c000ef          	jal	101f4 <get_instret>
   100cc:	00050913          	mv	s2,a0
   100d0:	110000ef          	jal	101e0 <get_cycles>
   100d4:	00050993          	mv	s3,a0
   100d8:	ffffe5b7          	lui	a1,0xffffe
   100dc:	12345537          	lui	a0,0x12345
   100e0:	ddd58593          	add	a1,a1,-547 # ffffdddd <__BSS_END__+0xfffe008d>
   100e4:	67850513          	add	a0,a0,1656 # 12345678 <__BSS_END__+0x12327928>
   100e8:	1b0000ef          	jal	10298 <efficient_int_mul>
   100ec:	00050493          	mv	s1,a0
   100f0:	00058413          	mv	s0,a1
   100f4:	0ec000ef          	jal	101e0 <get_cycles>
   100f8:	413505b3          	sub	a1,a0,s3
   100fc:	0001c537          	lui	a0,0x1c
   10100:	cb850513          	add	a0,a0,-840 # 1bcb8 <__clzsi2+0x72>
   10104:	704000ef          	jal	10808 <printf>
   10108:	0001c537          	lui	a0,0x1c
   1010c:	00090593          	mv	a1,s2
   10110:	ccc50513          	add	a0,a0,-820 # 1bccc <__clzsi2+0x86>
   10114:	6f4000ef          	jal	10808 <printf>
   10118:	0001c537          	lui	a0,0x1c
   1011c:	00048613          	mv	a2,s1
   10120:	00040693          	mv	a3,s0
   10124:	cdc50513          	add	a0,a0,-804 # 1bcdc <__clzsi2+0x96>
   10128:	6e0000ef          	jal	10808 <printf>
   1012c:	01c12083          	lw	ra,28(sp)
   10130:	01812403          	lw	s0,24(sp)
   10134:	01412483          	lw	s1,20(sp)
   10138:	01012903          	lw	s2,16(sp)
   1013c:	00c12983          	lw	s3,12(sp)
   10140:	00000513          	li	a0,0
   10144:	02010113          	add	sp,sp,32
   10148:	00008067          	ret

#### elf size

#### execute

- observe
- Total cycle count : `398`
- Total instruction count : `2c7`
- Register use : `$ra, $sp, $a0~$a7, $s0~$s3, $t1, $t4`

## Conclusion

|-|-O1|-O2|-O3|-Os|-Ofast|
|:-:|:-:|:-:|:-:|:-:|:-:|
|instret|2c7|2c7|2c7|**2c5**|2c7|
|Cycle|**393**|421|398|530|398|
|Code lines|132|131|181|**126**|181|

- Although the `instruction count` is similar between -`O1` and `-Ofast`, the cycle count is significantly reduced in `-O1`.
- `-Os` incurs the highest `cycle`, while `-O1` has the lowest, with a `decrease from 530 cycles to 393 cycles.`
- `-O3` and `-Ofast` use the most lines of code, while `-Os` uses the fewest.