1 2004 Morgan Kaufmann Publishers Chapter 2 Instructions: Language of the Computer.

12004 Morgan Kaufmann Publishers

Chapter 2Instructions: Language of the Computer


Outline

• 2.1 Introduction

• 2.2 Operations of the Computer Hardware

• 2.3 Operands of the Computer Hardware

• 2.4 Representing Instructions in the Computer

• 2.5 Logical Operations

• 2.6 Instructions for Making Decisions

• 2.7 Supporting Procedures in Computer Hardware

• 2.8 Communicating with People

• 2.9 MIPS Addressing for 32-Bits Immediates and Addresses

• 2.10 Translating and Starting a Program

• 2.16 Real Stuff: IA-32 Instructions

• Summary


2.1 Introduction


Four design principles guide• Simplicity favors regularity

• Smaller is faster

• Make the common case fast

• Good design demands good compromises


Instructions:

• Language of the Machine

• We’ll be working with the MIPS instruction set architecture

– similar to other architectures developed since the 1980's

– Almost 100 million MIPS processors manufactured in 2002

– used by NEC, Nintendo, Cisco, Silicon Graphics, Sony, …

1400

1300

1200

1100

1000

900

800

700

600

500

400

300

200

100

01998 2000 2001 20021999

Other

SPARC

Hitachi SH

PowerPC

Motorola 68K

MIPS

IA-32

ARM


Instruction set: The vocabulary of commands understood by a given architecture.

Stored-Program Concept : The idea that instructions and data of many types can be stored in memory as numbers, leading to the stored program computer.


2.2 Operations of the Computer Hardware


MIPS arithmetic

• All instructions have 3 operands

• Operand order is fixed (destination first)

Example:

C code: a = b + c

MIPS ‘code’: add a, b, c

(we’ll talk about registers in a bit)

“The natural number of operands for an operation like addition is three…requiring every instruction to have exactly three operands, no more and no less, conforms to the philosophy of keeping the hardware simple”


FIGURE 2.1 MIPS architecture revealed in section 2.2.

MIPS assembly language

Category Instruction Example Meaning Comments

Arithmetic add add a, b, c a = b + c Always three operands

subtract sub a, b, c a = b - c Always three operands


f = (g+h) - (i+j);

add t0, g, h

add t1, I, j

sub f, t0, t1


MIPS arithmetic

• Design Principle: simplicity favors regularity.

• Of course this complicates some things...

C code: a = b + c + d;

MIPS code: add a, b, cadd a, a, d

• Operands must be registers, only 32 registers provided

• Each register contains 32 bits

• Design Principle: smaller is faster. Why?


f = (g+h) - (i+j); $s0, $s1, $s2, $s3, $s4

add t0, $s1, $s2add t1, $s3, $s4sub $s0, t0, t1


2.3 Operands of the Computer Hardware


Data transfer instruction: a command that moves data between memory and registers.Address: A value used to delineate the location of a specific data element within a memory arry.Alignment restriction : A requirement that data be aligned in memory on natural boundaries.


Registers vs. Memory

Processor I/O

Control

Datapath

Memory

Input

Output

• Arithmetic instructions operands must be registers, — only 32 registers provided

• Compiler associates variables with registers

• What about programs with lots of variables


Memory Organization

• Viewed as a large, single-dimension array, with an address.

• A memory address is an index into the array

• "Byte addressing" means that the index points to a byte of memory.

0

1

2

3

4

5

6

...

8 bits of data

8 bits of data

8 bits of data

8 bits of data

8 bits of data

8 bits of data

8 bits of data


Memory Organization

• Bytes are nice, but most data items use larger "words"

• For MIPS, a word is 32 bits or 4 bytes.

• 232 bytes with byte addresses from 0 to 232-1

• 230 words with byte addresses 0, 4, 8, ... 232-4

• Words are alignedi.e., what are the least 2 significant bits of a word address?

0

4

8

12

...

32 bits of data

32 bits of data

32 bits of data

32 bits of data

Registers hold 32 bits of data


FIGURE 2.2 Memory addresses and contents of memory at those locations.


FIGURE 2.3 Actual MIPS memory addresses and contents of memory for those words.


g = h + A[8]

lw $t0, 8($s3)

add $s1, $s2, $t0


Instructions

• Load and store instructions• Example:

C code: A[12] = h + A[8];

MIPS code: lw $t0, 32($s3)add $t0, $s2, $t0sw $t0, 48($s3)

• Can refer to registers by name (e.g., $s2, $t2) instead of number• Store word has destination last• Remember arithmetic operands are registers, not memory!

Can’t write: add 48($s3), $s2, 32($s3)


Our First Example

• Can we figure out the code?

swap(int v[], int k);{ int temp;

temp = v[k]v[k] = v[k+1];v[k+1] = temp;

} swap:muli $2, $5, 4add $2, $4, $2lw $15, 0($2)lw $16, 4($2)sw $16, 0($2)sw $15, 4($2)jr $31


So far we’ve learned:

• MIPS— loading words but addressing bytes— arithmetic on registers only

• Instruction Meaning

add $s1, $s2, $s3 $s1 = $s2 + $s3sub $s1, $s2, $s3 $s1 = $s2 – $s3lw $s1, 100($s2) $s1 = Memory[$s2+100] sw $s1, 100($s2) Memory[$s2+100] = $s1


addi $s3, $s4, 4

# $s3 = $s3 +4


FIGURE 2.4 MIPS architecture revealed through section 2.3.

Name Example Comments

32 registers$s0, $s1, ……

$t 0, $t 1, ……Fast locations for data. In MIPS, data must be in registers to perform arithmetic.

memory words

Memory[0],

Memory[4], …,

Memory[4294967292]

Accessed only by data transfer instructions in MIPS. MIPS uses byte addresses,

so sequential word addresses differ by 4. Memory holds data structures arrays,

and spilled registers.

MIPS operands

302

MIPS assembly languageCategory Instruction Example Meaning Comments

Arithmetic

add add $s1, $s2, $s3 $s1 = $s2 + $s3 Three operands; data in registers

subtract sub $s1, $s2, $s3 $s1 = $s2 - $s3 Three operands; data in registers

add immediate addi $s1, $s2, 100 $s1 = $s2 + 100 Used to add constants

Data transferload word lw $s1, 100($s2) $s1 = Memory [$s2 + 100] Data from memory to register

store word sw $s1, 100 ($s2) Memory [$s2 + 100] = $s1 Data from register to memory


2.4 Representing Instructions in the Computer


Binary digit Also called binary bit. One of the two numbers in base 2, 0 or 1, that are the components of information.

Machine language: Binary representation used for communication within a computer system.

Instruction format: A form of representation of an instruction composed of fields of binary numbers.


• Instructions, like registers and words of data, are also 32 bits long

– Example: add $t1, $s1, $s2– registers have numbers, $t1=9, $s1=17, $s2=18

• Instruction Format:

000000 10001 10010 01000 00000 100000

op rs rt rd shamt funct

• Can you guess what the field names stand for?

Machine Language


• Consider the load-word and store-word instructions,

– What would the regularity principle have us do?

– New principle: Good design demands a compromise

• Introduce a new type of instruction format

– I-type for data transfer instructions

– other format was R-type for register

• Example: lw $t0, 32($s2)

35 18 9 32

op rs rt 16 bit number

• Where's the compromise?

Machine Language


op: Opcode

rs: the first register source operand.

rt: the second register source operand.

rd: the destination operand.

shamt: Shift amount.

funct: Function (function code).


• Instructions are bits• Programs are stored in memory

— to be read or written just like data

• Fetch & Execute Cycle– Instructions are fetched and put into a special register– Bits in the register "control" the subsequent actions– Fetch the “next” instruction and continue

Processor Memory

memory for data, programs, compilers, editors, etc.

Stored Program Concept


• Decision making instructions

– alter the control flow,

– i.e., change the "next" instruction to be executed

• MIPS conditional branch instructions:

bne $t0, $t1, Label beq $t0, $t1, Label

• Example: if (i==j) h = i + j;

bne $s0, $s1, Labeladd $s3, $s0, $s1

Label: ....

Control


• MIPS unconditional branch instructions:j label

• Example:

if (i!=j) beq $s4, $s5, Lab1 h=i+j; add $s3, $s4, $s5else j Lab2 h=i-j; Lab1: sub $s3, $s4, $s5

Lab2: ...

• Can you build a simple for loop?

Control


So far:

• Instruction Meaning

add $s1,$s2,$s3 $s1 = $s2 + $s3sub $s1,$s2,$s3 $s1 = $s2 – $s3lw $s1,100($s2) $s1 = Memory[$s2+100] sw $s1,100($s2) Memory[$s2+100] = $s1bne $s4,$s5,L Next instr. is at Label if $s4 ≠ $s5beq $s4,$s5,L Next instr. is at Label if $s4 = $s5j Label Next instr. is at Label

• Formats:


op rs rt 16 bit address

op 26 bit address

R

I

J


FIGURE 2.7 MIPS architecture revealed through section 2.4

Name Example Comments

32 registers$s0, $s1, …, $s7

$t 0, $t 1, …, $t 7

Fast locations for data. In MIPS, data must be in registers to perform arithmetic.

Registers $s0 - $s7 map to 16-23 and $t0 - $t7 map to 8-15.

memory words

Memory[0],

Memory[4], …,

Memory[4294967292]

Accessed only by data transfer instructions in MIPS. MIPS uses byte addresses,

so sequential word addresses differ by 4. Memory holds data structures arrays,

and spilled registers.

MIPS operands

302


Arithmeticadd add $s1, $s2, $s3 $s1 = $s2 + $s3 Three operands; data in registers

subtract sub $s1, $s2, $s3 $s1 = $s2 - $s3 Three operands; data in registers





MIPS machine languageName Format Example Comments

add R 0 18 19 17 0 32 add $s1, $s2, $s3

sub R 0 18 19 17 0 34 sub $s1, $s2, $s3

addi I 8 18 17 100 addi $s1, $s2, 100

lw I 35 18 17 100 lw $s1, 100($s2)

sw I 43 18 17 100 sw $s1, 100 ($s2)

Field size 6 bits 5 bits 5 bits 5 bits 5 bits 6 bits ALL MIPS instructions 32 bits

R-format R op rs rt rd shamt funct Arithmetic instruction format

I-format I op rs rt address Data transfer format


FIGURE 2.8 The stored-program concept.


• We have: beq, bne, what about Branch-if-less-than?

• New instruction:if $s1 < $s2 then

$t0 = 1 slt $t0, $s1, $s2 else

$t0 = 0

• Can use this instruction to build "blt $s1, $s2, Label" — can now build general control structures

• Note that the assembler needs a register to do this,— there are policy of use conventions for registers

Control Flow


2.5 Logical Operations


FIGURE 2.9 C and JAVA logical operators and their corresponding MIPS instructions.

Logical operations C operators JAVA operators MIPS instructions

Shift left << << sll

Shift right >> >>> srl

Bit-by-bit AND & & and, andi

Bit-by-bit OR | | or, ori

Bit-by-bit NOT ~ ~ nor


FIGURE 2.10 MIPS architecture revealed thus far.

MIPS operandsName Example Comments

32 registers$s0, $s1, …, $s7

$t 0, $t 1, …, $t 7


Registers $s0 - $s7 map to 16-23 and $t0 - $t7 map to 8-15.

memory words

Memory[0],Memory[4], …, Memory[4294967292]

Accessed only by data transfer instructions in MIPS. MIPS uses byte addresses, so sequential word addresses differ by 4. Memory holds data structures arrays, and spilled registers.

302



Arithmetic

add add $s1, $s2, $s3 $s1 = $s2 + $s3 Three operands; Overflow detected

subtract sub $s1, $s2, $s3 $s1 = $s2 - $s3 Three operands; Overflow detected

add immediate addi $s1, $s2, 100 $s1 = $s2 + 100 +constant; overflow detected

Logical

and add $s1, $s2, $s3 $s1 = $s2 & $s3 Three reg. operands; bit-by-bit AND

or or $s1, $s2, $s3 $s1 = $s2 | $s3 Three reg. operands; bit-by-bit OR

nor nor $s1, $s2, $s3 $s1 = ~($s2 | $s3) Three reg. operands; bit-by-bit NOR

and immediate andi $s1, $s2, 100 $s1 = $s2 & 100 Bit-by-bit AND reg with constant

or immediate ori $s1, $s2, 100 $s1 = $s2 | 100 Bit-by-bit OR reg with constant

shift left logical sll $s1, $s2, 10 $s1 = $s2 << 10 Shift left by constant

shift right logical

srl $$s1, $s2, 10 $s1 = $s2 >> 10 Shift right by constant

Data transfer

load word lw $s1, 100($s2) $s1 = Memory [$s2 + 100] Word from memory to register

store word sw $s1, 100 ($s2) Memory [$s2 + 100] = $s1 Word from register to memory



2.6 Instructions for Making Decisions


Conditional branch: An Instruction that requires the comparison of two values and that allows for a subsequent transfer of control to a new address in the program based on the outcome of the comparison.Basic block: A sequence of instructions without branches and without branch targets or branch labels.Jump address table also called jump table. A table of addresses of alternative instruction sequences.


FIGURE 2.11 Illustration of the options in the IF statement above.


Compiling if-then-else into Conditional Branches

if (i==j) f=g+h; else f=g-h;

bne $s3, $s4, Else

add $s0, $s1, $s2

j Exit

Else: sub $s0, $s1, $s2

Exit:


Compiling a while loop in C

while (save[i]==k)

i+=1;

Loop: sll $t1, $s3,2

add $t1, $t1, $s6

lw $t0, 0($t1)

bne $t0, $s5, Exit

add $s3, $s3, 1

j Loop

Exit:


The MIPS instruction is called set on less than

slt $t0, $s3, $s4means that register $t0 is set to 1 if the value in register $s3 is less than the value in register $s4; otherwise, register $t0 is set to o.

slti $t0, $s2, 10




32 registers

$s0, $s1, …, $s7

$t 0, $t 1, …, $t 7

$zero


Registers $s0 - $s7 map to 16-23 and $t0 - $t7 map to 8-15. MIPS register $zero always equals 0.

memory words


Accessed only by data transfer instructions in MIPS. MIPS uses byte addresses, so sequential word addresses differ by 4. Memory holds data structures arrays, and spilled registers.

302


FIGURE 2.13 MIPS machine language revealed through section 2.6.


add R 0 18 19 17 0 32 add $s1, $s2, $s3

sub R 0 18 19 17 0 34 sub $s1, $s2, $s3

lw I 35 18 17 100 lw $s1, 100($s2)

sw I 43 18 17 100 sw $s1, 100 ($s2)

and R 0 18 19 17 0 36 and $s1, $s2, $s3

or R 0 18 19 17 0 37 or $s1, $s2, $s3

nor R 0 18 19 17 0 39 nor $s1, $s2, $s3

andi I 12 18 17 100 andi $s1, $s2, 100

ori I 13 18 17 100 ori $s1, $s2, 100

sll R 0 0 18 17 10 0 sll $s1, $s2, 10

srl R 0 0 18 17 10 2 srl $s1, $s2, 10

beq I 4 17 18 25 beq $s1, $s2, 100

bne I 5 17 18 25 bne $s1, $s2, 100

slt R 0 18 19 17 0 42 slt $s1, $s2, $s3

j J 2 2500 j 10000 (see Section 2.9)



I-format I op rs rt address Data transfer, branch format


Policy of Use Conventions

Name Register number Usage$zero 0 the constant value 0$v0-$v1 2-3 values for results and expression evaluation$a0-$a3 4-7 arguments$t0-$t7 8-15 temporaries$s0-$s7 16-23 saved$t8-$t9 24-25 more temporaries$gp 28 global pointer$sp 29 stack pointer$fp 30 frame pointer$ra 31 return address

Register 1 ($at) reserved for assembler, 26-27 for operating system


• Small constants are used quite frequently (50% of operands) e.g., A = A + 5;

B = B + 1;C = C - 18;

• Solutions? Why not?– put 'typical constants' in memory and load them. – create hard-wired registers (like $zero) for constants like one.

• MIPS Instructions:

addi $29, $29, 4slti $8, $18, 10andi $29, $29, 6ori $29, $29, 4

• Design Principle: Make the common case fast. Which format?

Constants


• We'd like to be able to load a 32 bit constant into a register

• Must use two instructions, new "load upper immediate" instruction

lui $t0, 1010101010101010

• Then must get the lower order bits right, i.e.,

ori $t0, $t0, 1010101010101010

1010101010101010 0000000000000000

0000000000000000 1010101010101010

1010101010101010 1010101010101010

ori

1010101010101010 0000000000000000

filled with zeros

How about larger constants?


• Assembly provides convenient symbolic representation

– much easier than writing down numbers

– e.g., destination first

• Machine language is the underlying reality

– e.g., destination is no longer first

• Assembly can provide 'pseudoinstructions'

– e.g., “move $t0, $t1” exists only in Assembly

– would be implemented using “add $t0,$t1,$zero”

• When considering performance you should count real instructions

Assembly Language vs. Machine Language


• Discussed in your assembly language programming lab: support

for procedures

linkers, loaders, memory layout

stacks, frames, recursion

manipulating strings and pointers

interrupts and exceptions

system calls and conventions

• Some of these we'll talk more about later

• We’ll talk about compiler optimizations when we hit chapter 4.

Other Issues


• simple instructions all 32 bits wide

• very structured, no unnecessary baggage

• only three instruction formats

• rely on compiler to achieve performance— what are the compiler's goals?

• help compiler where we can



op 26 bit address

R

I

J

Overview of MIPS


FIGURE 2.13 MIPS machine language revealed through section 2.6.


add R 0 18 19 17 0 32 add $s1, $s2, $s3

sub R 0 18 19 17 0 34 sub $s1, $s2, $s3

lw I 35 18 17 100 lw $s1, 100($s2)

sw I 43 18 17 100 sw $s1, 100 ($s2)

and R 0 18 19 17 0 36 and $s1, $s2, $s3

or R 0 18 19 17 0 37 or $s1, $s2, $s3

nor R 0 18 19 17 0 39 nor $s1, $s2, $s3

andi I 12 18 17 100 andi $s1, $s2, 100

ori I 13 18 17 100 ori $s1, $s2, 100

sll R 0 0 18 17 10 0 sll $s1, $s2, 10

srl R 0 0 18 17 10 2 srl $s1, $s2, 10

beq I 4 17 18 25 beq $s1, $s2, 100

bne I 5 17 18 25 bne $s1, $s2, 100

slt R 0 18 19 17 0 42 slt $s1, $s2, $s3

j J 2 2500 j 10000 (see Section 2.9)





2.7 Supporting Procedures in Computer Hardware


Procedure: A stored subroutine that performs a specific task based on the parameters with which it is provided.

Jump-and-link instruction: An instruction that jumps to an address and simultaneously saves the address of the following instruction in a register ($ra in MIPS)

Return address: A link to the calling site that allows a procedure to return to the proper address; in MIPS it is stored in register $ra.

Program Counter (PC): The register containing the address of the instruction in the program being executed.


Caller: The program that instigates a procedure and provides the necessary parameter values.

Callee: A procedure that executes a series of stored instructions based on parameters provided by the caller and then returns control to the caller.

Stack: A data structure for spilling registers organized as a last-in-first-out queue.

Stack pointer: A value denoting the most recently allocated address in a stack that shows where registers should be spilled or where old register values can be found.


• Instructions:

bne $t4,$t5,Label Next instruction is at Label if $t4 ° $t5

beq $t4,$t5,Label Next instruction is at Label if $t4 = $t5

j Label Next instruction is at Label

• Formats:

• Addresses are not 32 bits — How do we handle this with load and store instructions?


op 26 bit address

I

J

Addresses in Branches and Jumps


• Instructions:

bne $t4,$t5,Label Next instruction is at Label if $t4≠$t5beq $t4,$t5,Label Next instruction is at Label if $t4=$t5

• Formats:

• Could specify a register (like lw and sw) and add it to address

– use Instruction Address Register (PC = program counter)

– most branches are local (principle of locality)

• Jump instructions just use high order bits of PC

– address boundaries of 256 MB

op rs rt 16 bit addressI

Addresses in Branches


To summarize:MIPS operands

Name Example Comments$s0-$s7, $t0-$t9, $zero, Fast locations for data. In MIPS, data must be in registers to perform

32 registers $a0-$a3, $v0-$v1, $gp, arithmetic. MIPS register $zero always equals 0. Register $at is $fp, $sp, $ra, $at reserved for the assembler to handle large constants.

Memory[0], Accessed only by data transfer instructions. MIPS uses byte addresses, so

230

memory Memory[4], ..., sequential words differ by 4. Memory holds data structures, such as arrays,

words Memory[4294967292] and spilled registers, such as those saved on procedure calls.


Category Instruction Example Meaning Commentsadd add $s1, $s2, $s3 $s1 = $s2 + $s3 Three operands; data in registers

Arithmetic subtract sub $s1, $s2, $s3 $s1 = $s2 - $s3 Three operands; data in registers

add immediate addi $s1, $s2, 100 $s1 = $s2 + 100 Used to add constants

load word lw $s1, 100($s2) $s1 = Memory[$s2 + 100] Word from memory to register

store word sw $s1, 100($s2) Memory[$s2 + 100] = $s1 Word from register to memory

Data transfer load byte lb $s1, 100($s2) $s1 = Memory[$s2 + 100] Byte from memory to register

store byte sb $s1, 100($s2) Memory[$s2 + 100] = $s1 Byte from register to memory

load upper immediate lui $s1, 100 $s1 = 100 * 216 Loads constant in upper 16 bits

branch on equal beq $s1, $s2, 25 if ($s1 == $s2) go to PC + 4 + 100

Equal test; PC-relative branch

Conditional

branch on not equal bne $s1, $s2, 25 if ($s1 != $s2) go to PC + 4 + 100

Not equal test; PC-relative

branch set on less than slt $s1, $s2, $s3 if ($s2 < $s3) $s1 = 1; else $s1 = 0

Compare less than; for beq, bne

set less than immediate

slti $s1, $s2, 100 if ($s2 < 100) $s1 = 1; else $s1 = 0

Compare less than constant

jump j 2500 go to 10000 Jump to target address

Uncondi- jump register jr $ra go to $ra For switch, procedure return

tional jump jump and link jal 2500 $ra = PC + 4; go to 10000 For procedure call


The six steps of the execution of a procedure

1. Place parameter in a place where the procedure can access them.

2. Transfer control to the procedure

3. Acquire the storage resources needed for the procedure.

4. perform the desired task.

5. place the result value in a place where the calling program can access it.

6. Return control to the point of origin, since a procedure can be called from several points in a program.


Registers for procedure calling:

• $a0-$a3: four argument registers in which to pass parameters

• $v0-$v1: two value registers in which to return values

• $ra: one return address register to return to the point of origin

• $t0-$t9: 10 temporary registers that are not preserved by the callee on a procedure call

• $s0-$s7: 8 saved registers that must be preserved on a procedure call


Compiling a C procedure(Doesn’t Call Another)

Int leaf_example (int g, int h, int i, int j) { int f:

f=(g+h)-(i+j);return f;}

leaf_example:addi $sp, $sp, -12sw $t1, 8($sp)sw $t0, 4($sp)sw $s0, 0($sp)add $t0, $a0, $a1add $t1, $a2, $a3sub $s0, $t0, $t1add $v0, S0, $zerolw $s0, 0($sp)lw $t0, 4($sp)lw $t1, 8($sp)addi $sp, $sp, 12jr $ra


Compiling a Recursive C Procedure

Int fact (int n) { if (n<1) return (1);

else return (n*fact(n-1));}fact:

addi $sp, $sp, -8sw $ra, 4($sp)sw $a0, 0($sp)slti $t0, $a0, 1beq $t0, $zero, L1addi $v0, $zero, 1addi $sp, $sp, 8jr $ra

L1: addi $a0, $a0, -1jalfactlw $a0, 0($sp)lw $ra, 4($sp)addi $sp, $sp, 8mul $v0, $a0, $v0jr $ra


FIGURE 2.14 The values if the stack pointer and the stack (a) before, (b) during, and (c) after the procedure call


FIGURE 2.15 What is and what is not preserved across a procedure call.

Preserved Not preserved

Saved registers: $s0 - $s7 Temporary registers: $t 0-$t 9

Stack pointer register: $sp Argument registers: $a0 - $a3

Return address register: $ra Return value registers: $v0 - $v1

Stack above the stack pointer Stack below the stack pointer


FIGURE 2.16 Illustration of the stack allocation (a) before, (b) during, and (c) after the procedure call.


FIGURE 2.17 The MIPS memory allocation for program and data.


FIGURE 2.18 MIPS register conventions.

Name Register number UsagePreserved on

call?

$zero 0 the constant value 0 n.a.

$v0-$v1 2-3 values for results and expression evaluation

no

$a0-$a3 4-7 arguments no

$t0-$t7 8-15 temporaries no

$s0-$s7 16-23 saved yes

$t8-$t9 24-25 more temporaries no

$gp 28 global pointer yes

$sp 29 stack pointer yes

$fp 30 frame pointer yes

$ra 31 return address yes


FIGURE 2.19 MIPS architecture revealed through section 2.7.


32 registers$s0-$s7, $t 0- $t 9,

$zero, $a0-a3, $v0-$v1, $gp, $fp, $sp, $ra


MIPS register $zero always equals 0. $gp (28) is the global pointer, $sp (29) is the stack pointer, $fp (30) is the frame pointer, and $ra (31) is the return address.

memory words


Accessed only by data transfer instructions in MIPS. MIPS uses byte addresses, so sequential word addresses differ by 4. Memory holds data structures, arrays, and spilled registers, such as those saved on procedure calls.

302



Arithmeticadd add $s1, $s2, $s3 $s1 = $s2 + $s3 Three operands; Overflow detected




Logical







shift right logical srl $$s1, $s2, 10 $s1 = $s2 >> 10 Shift right by constant

Conditional branch

branch on equal beq $s1, $s2, L if ($s1 == $s2) go to L Equal test and branch

branch on not equal

bne $s1, $s2, L if ($s1 != $s2) go to L Not equal test and branch

set on less than slt $s1, $s2, $s3 if ($s2 < $s3) $s1 = 1;

else $s1 = 0

Compare less than; used with beq, bne

set on less than immediate

slt $s1, $s2, 100 if ($s2 < 100) $s1 = 1;

else $s1 = 0

Compare less than immediate; used with beq, bne

Unconditional jump

jump j L go to L Jump to target address

jump register jr $ra go to $ra For procedure return

jump and link jal L $ra = PC + 4; go to L For procedure call


FIGURE 2.20 MIPS machine language revealed through section 2.7.Name Format Example Comments

add R 0 18 19 17 0 32 add $s1, $s2, $s3

sub R 0 18 19 17 0 34 sub $s1, $s2, $s3

lw I 35 18 17 100 lw $s1, 100($s2)

sw I 43 18 17 100 sw $s1, 100 ($s2)

and R 0 18 19 17 0 36 and $s1, $s2, $s3

or R 0 18 19 17 0 37 or $s1, $s2, $s3

nor R 0 18 19 17 0 39 nor $s1, $s2, $s3

andi I 12 18 17 100 andi $s1, $s2, 100

ori I 13 18 17 100 ori $s1, $s2, 100

sll R 0 0 18 17 10 0 sll $s1, $s2, 10

srl R 0 0 18 17 10 2 srl $s1, $s2, 10

beq I 4 17 18 25 beq $s1, $s2, 100

bne I 5 17 18 25 bne $s1, $s2, 100

slt R 0 18 19 17 0 42 slt $s1, $s2, $s3

j J 2 2500 j 10000 (see Section 2.9)

jr R 0 31 0 0 0 8 jr $ra

jal J 3 2500 jal 10000 (see section 2.9)





2.8 Communicating with People


Instructions to move bytes

lb $t0, 0($sp); Loads a bytes from memory, placing it in the rightmost 8 bits of a register.

sb $t0, 0($gp); Stores a bytes from the rightmost 8 bits of a register, placing it to memory.


FIGURE 2.21 ASCII representation of characters.

ASCII value

Char-acter

ASCII value

Char-acter

ASCII value

Char-acter

ASCII value

Char-acter

ASCII value

Char-acter

ASCII value

Char-acter

32 space 48 0 64 @ 80 P 96 ` 112 p

33 ! 49 1 65 A 81 Q 97 a 113 q

34 “ 50 2 66 B 82 R 98 b 114 r

35 # 51 3 67 C 83 S 99 c 115 s

36 $ 52 4 68 D 84 T 100 d 116 t

37 % 53 5 69 E 85 U 101 e 117 u

38 & 54 6 70 F 86 V 102 f 118 v

39 ‘ 55 7 71 G 87 W 103 g 119 w

40 ( 56 8 72 H 88 X 104 h 120 x

41 ) 57 9 73 I 89 Y 105 I 121 y

42 * 58 : 74 J 90 Z 106 j 122 z

43 + 59 ; 75 K 91 [ 107 k 123 {

44 , 60 < 76 L 92 \ 108 l 124 |

45 - 61 = 77 M 93 ] 109 m 125 }

46 . 62 > 78 N 94 ^ 110 n 126 ~

47 / 63 ? 79 O 95 _ 111 o 127 DEL


2.9 MIPS Addressing for 32-Bits Immediates and Addresses


FIGURE 2.23 The effect of the lui instruction.

The machine language version of lui $t0, 255 # $t0 is register 8:

001111 00000 01000 0000000011111111

Contents of register $t0 after executing lui $t0, 255:

0000 0000 1111 1111 0000000011111111


Loading a 32-bit Constant

Load 0000 0000 0011 1101 0000 1001 0000 0000 to register $s0

lui $s0, 61 #61 decimal = 0000 0000 0011 1101

ori $s0, $s0, 2304 #2304 decimal = 0000 1001 0000 0000


MIPS Addressing Mode Summary

1. Register addressing,

2. Base or displacement addressing,

3. Immediate addressing,

4. PC-relative addressing,

5. Pseudodirect addressing,


Byte Halfword Word

Registers

Memory

Memory

Word

Memory

Word

Register

Register

1. Immediate addressing

2. Register addressing

3. Base addressing

4. PC-relative addressing

5. Pseudodirect addressing

op rs rt

op rs rt

op rs rt

op

op

rs rt

Address

Address

Address

rd . . . funct

Immediate

PC

PC

+

+

FIGURE 2.24 Illustration of the five MIPS addressing modes.


FIGURE 2.25 MIPS instruction encoding

Op (31:26)

28-26

31-29

0(000) 1(001) 2(010) 3(011) 4(100) 5(101) 6(110)

7(111)

0(000)

R-format Bltz/gez jump Jump & link

branch eq

branch blez bgtz

1(001)

add

immediate

addiu set less

than imm.

sltiu andi ori xori load upper imm

2(010)

TLB FLPt

3(011)

4(100)

load byte load half lw1 load word lbu lhu lwr

5(101)

store byte store half

sw1 store word swr

6(110)

lwc0 lwc1

7(111)

swc0 swc1


Op (31:26)=010000 (TLB), rs(25:21)

23-21

25-24

0(000) 1(001) 2(010) 3(011) 4(100) 5(101) 6(110)

7(111)

0(00) mfc0 cfc0 mtc0 ctc0

1(01)

2(10)

3(11)


Op (31:26)=000000 (R-format), funct(5:0)

2 - 0

5 – 3

0(000) 1(001) 2(010) 3(011) 4(100) 5(101) 6(110)

7(111)

0(000)

shift left logical

shift right logical

sra sllv srlv srav

1(001)

jump reg. jalr syscall break

2(010)

mfhi mthi mflo mtlo

3(011)

mult multu div divu

4(100)

add addu subtract subu and or xor not or (nor)

5(101)

set l . t . sltu

6(110)

7(111)


FIGURE 2.26 MIPS instruction formats in Chapter 2.

Name Fields Comments


R-format op rs rt rd shamt funct Arithmetic instruction format

I-format op rs rt address/immediate Transfer, brance, imm. format

J-format op target address jump instruction format


FIGURE 2.27 MIPS assembly language revealed in Chapter 2.


32 registers$s0-$s7, $t 0- $t 9,

$zero, $a0-a3, $v0-$v1, $gp, $fp, $sp, $ra, $at


MIPS register $zero always equals 0. Register $at is reserved for the assembler to handle large constants.

memory words


Accessed only by data transfer instructions in MIPS. MIPS uses byte addresses, so sequential word addresses differ by 4. Memory holds data structures, arrays, and spilled registers, such as those saved on procedure calls.




Arithmetic

add add $s1, $s2, $s3 $s1 = $s2 + $s3 Three operands; Overflow detected


add immediate addi $s1, $s2, 100 $s1 = $s2+ 100 Used to add constants

Data transfer

load word lw $s1, 100($s2) $s1 = Memory [$s2 + 100] Word from memory to register

store word sw $s1, 100 ($s2) Memory [$s2 + 100] = $s1 Word from register to memory

load half lh $s1, 100($s2) $s1 = Memory [$s2 + 100] Halfword memory to register

store half sh $s1, 100 ($s2) Memory [$s2 + 100] = $s1 Halfword register to memory

load byte lb $s1, 100($s2) $s1 = Memory [$s2 + 100] Byte from memory to register

store byte sb $s1, 100 ($s2) Memory [$s2 + 100] = $s1 Byte from register to memory

load upper immed. lui $s1, 100 $s1 = 100 * 2^16 Loads constant in upper 16 bits

Logical







shift right logical srl $$s1, $s2, 10 $s1 = $s2 >> 10 Shift right by constant


Continue..

Conditional branch

branch on equal beq $s1, $s2, 25 if ($s1 == $s2) go to

PC+4+100

Equal test; PC-relative branch

branch on not equal

bne $s1, $s2, 25 if ($s1 != $s2) go to L

PC+4+100

Not equal test; PC-relative

set on less than slt $s1, $s2, $s3 if ($s2 < $s3) $s1 = 1;

else $s1 = 0

Compare less than; for beq, bne

set on less than immediate

slt $s1, $s2, 100 if ($s2 < 100) $s1 = 1;

else $s1 = 0

Compare less than constant

Unconditional jump

jump j 2500 go to 10000 Jump to target address

jump register jr $ra go to $ra For procedure return

jump and link jal 2500 $ra = PC + 4; go to 10000 For procedure call


2.10 Translating and Starting a Program


• Pseudoinstruction: A common variation of assembly language instructions often treated as if it were an instruction in its own right.

• Symbol table: A table that matches names of labels to the addresses of the memory words that instructions occupy.

• Linker Also called link editor: A systems program that combines independtly assembled machine language programs and resolves all undefined labels into an executable file.

• Executable file: A functional program in the format of an object file that contains no unresolved references, relocation information, symbol table, or debugging information.

• Loader: A systems program that places an object program in main memory so that it is ready to execute.


FIGURE 2.28 A translation hierarchy for C.


FIGURE 2.29 Dynamically linked library via lazy procedure linkage.


FIGURE 2.30 A translation hierarchy for JAVA.


2.16 Real Stuff: IA-32 Instructions


• Design alternative:

– provide more powerful operations

– goal is to reduce number of instructions executed

– danger is a slower cycle time and/or a higher CPI

• Let’s look (briefly) at IA-32

Alternative Architectures

–“The path toward operation complexity is thus fraught with peril.

To avoid these problems, designers have moved toward simpler

instructions”


IA - 32

• 1978: The Intel 8086 is announced (16 bit architecture)• 1980: The 8087 floating point coprocessor is added• 1982: The 80286 increases address space to 24 bits, +instructions• 1985: The 80386 extends to 32 bits, new addressing modes• 1989-1995: The 80486, Pentium, Pentium Pro add a few instructions

(mostly designed for higher performance)• 1997: 57 new “MMX” instructions are added, Pentium II• 1999: The Pentium III added another 70 instructions (SSE)• 2001: Another 144 instructions (SSE2)• 2003: AMD extends the architecture to increase address space to 64 bits,

widens all registers to 64 bits and other changes (AMD64)• 2004: Intel capitulates and embraces AMD64 (calls it EM64T) and adds

more media extensions

• “This history illustrates the impact of the “golden handcuffs” of compatibility

“adding new features as someone might add clothing to a packed bag”

“an architecture that is difficult to explain and impossible to love”


IA-32 Overview

• Complexity:

– Instructions from 1 to 17 bytes long

– one operand must act as both a source and destination

– one operand can come from memory

– complex addressing modese.g., “base or scaled index with 8 or 32 bit

displacement”

• Saving grace:

– the most frequently used instructions are not too difficult to build

– compilers avoid the portions of the architecture that are slow

“what the 80x86 lacks in style is made up in quantity, making it beautiful from the right perspective”


IA-32 Registers and Data Addressing

• Registers in the 32-bit subset that originated with 80386

GPR 0

GPR 1

GPR 2

GPR 3

GPR 4

GPR 5

GPR 6

GPR 7

Code segment pointer

Stack segment pointer (top of stack)

Data segment pointer 0




Instruction pointer (PC)

Condition codes

Use

031Name

EAX

ECX

EDX

EBX

ESP

EBP

ESI

EDI

CS

SS

DS

ES

FS

GS

EIP

EFLAGS


IA-32 Register Restrictions

• Registers are not “general purpose” – note the restrictions below


IA-32 Typical Instructions

• Four major types of integer instructions:

– Data movement including move, push, pop

– Arithmetic and logical (destination register or memory)

– Control flow (use of condition codes / flags )

– String instructions, including string move and string compare


IA-32 instruction Formats

• Typical formats: (notice the different lengths)

a. JE EIP + displacement

b. CALL

c. MOV EBX, [EDI + 45]

d. PUSH ESI

e. ADD EAX, #6765

f. TEST EDX, #42

ImmediatePostbyteTEST

ADD

PUSH

MOV

CALL

JE

w

w ImmediateReg

Reg

wd Displacementr/m

Postbyte

Offset

DisplacementCondi-tion

4 4 8

8 32

6 81 1 8

5 3

4 323 1

7 321 8


• Instruction complexity is only one variable

– lower instruction count vs. higher CPI / lower clock rate

• Design Principles:

– simplicity favors regularity

– smaller is faster

– good design demands compromise

– make the common case fast

• Instruction set architecture

– a very important abstraction indeed!

Summary

1 2004 Morgan Kaufmann Publishers Chapter 2 Instructions: Language of the Computer.

Documents

Transcript of 1 2004 Morgan Kaufmann Publishers Chapter 2 Instructions: Language of the Computer.