Intermediate Code Generation - Compiler Design and Implementation | CS 5810, Papers of Computer Science

Download Intermediate Code Generation - Compiler Design and Implementation | CS 5810 and more Papers Computer Science in PDF only on Docsity!

Intermediate

‐Code Generation

Intermediate

‐Code

Generation

Chapter

Chapter^ 6:^ Intermediate

Code Generation^

CS5810^ Spring^

2009

Why Intermediate CodeWhy

Intermediate

Code

I t^ di t

Parser^

Static Checker

Intermediate^ Code^ Generator

Code Generator

Front^ end

Back^ end

Program^1

Architecture

1

Program^1

Architecture

1

Program^1

Architecture

2

Program^1

Architecture

2 Interm.^ C d

Program^1 Program

Architecture

3 Architecture

Program^1 Program

Architecture

3 Architecture Code

Chapter^ 6:^ Intermediate

Code Generation^

CS5810^ Spring^

2009

Program^1

Architecture

4

Program^1

Architecture

4

Intermediate language levelsIntermediate

language

levels

Hi h^

-^ Medium -^ Low -^ High t1^ Å^ a[i,j+2] -^ Mediumt1^ Å

j^ +^2 t2 Å i * 20

• Lowr1^ Å

[fp‐4] r2 Å r1 + 2

t2^ Å^ i

*^20 t3^ Å^ t

+^ t t4^ Å^ 4 * t

r2^ Å^ r

+^2 r3^ Å^ [fp

‐8] 4 Å^ 3*

t4^ Å^4

*^ t t5^ Å^ addr

a Å

r4^ Å^ r3*20r5^ Å^ r

+^ r2 Å *

t6^ Å^ t

+^ t^4 t7^ Å^ *t

r6^ Å^4

*^ r r7^ Å^ fp

• 216 f1^ Å^ [r7+r6]

Chapter^ 6:^ Intermediate

Code Generation^

CS5810^ Spring^

2009

Intermediate Languages TypesIntermediate

Languages

Types

-^ Graphical IRs: Abstract Syntax trees DAGsGraphical

IRs:^ Abstract

Syntax

trees

,^ DAGs

Control

Flow^

Graphs

-^ Linear IRs:•^ Linear

IRs:

-^ Stack

based

(postfix) Th^

dd^

d^ (^

d^ l^

)

-^ Three

address

code^ (

quadruples)

Chapter^ 6:^ Intermediate

Code Generation^

CS5810^ Spring^

2009

ASTs^

and^ DAGs:b *^

b*

a^ :=^ b

*‐c^ +

b*‐c

:= a +

:= a +

*^ * b (uni)^

(uni)b

• (uni)b

b^ ‐^ (uni)

‐^ (uni)b c

‐^ (uni)b

c^

c

Chapter^ 6:^ Intermediate

Code Generation^

CS5810^ Spring^

2009

DAGs for ExpressionsDAGs

for^

Expressions

-^ A node in a Directed Acyclic Graph (DAG) mayA^ node

in^ a^ Directed

Acyclic

Graph

(DAG)

may

have^ more

than^

one^ parent

• *+

d *^ ‐ a

a+a*(b

‐c)+(b

‐c)*d

c b

Chapter^ 6:^ Intermediate

Code Generation^

CS5810^ Spring^

2009

Value

‐number method for DAG

Value

number

method

for^

DAG

id 1 num+

(^1021) 2 3 = +

i =^ i^ +^

=^

1 3 4 5 (^10) i

Input: Label op, node l, and node rOutput: The value number in the array with <op, l, r>Method: Search the array for M=<op, l, r>. If M exists, return M;otherwise create a new node N=<op, l, r>, and return its valuenumber

CS5810^ Spring^

2009

number. Chapter^ 6:^ Intermediate

Code Generation

TEST YOURSELF #1TEST

YOURSELF

-^ Construct the DAG and identify the valueConstruct

the^ DAG

and^ identify

the^ value

numbers

for^ the

sub‐expressions ((x+y)

‐((x+y)*(x

‐y)))+((x+y)*(x

‐y)) CS5810^ Spring^

2009

Chapter^ 6:^ Intermediate

Code Generation

Three

‐Address Code

Three

Address

Code

-^ At most one operator on the right hand sideAt^ most

one^ operator

on^ the

right^

hand^

side

-^ Expression

like^ x+y*z

has^ to

be^ translated

• *+

t^ =b‐c^1 t^ =a*t^2

1

d *^ ‐ a

t^ a t^2

1 t^ =a+t^3

2 t^ =t^ *d^41

c b

t^ t^4

d t^ =t^ +t^53

4

Chapter^ 6:^ Intermediate

Code Generation^

CS5810^ Spring^

2009

Addresses and InstructionsAddresses

and

Instructions

-^ An address can beAn^

address

can^ be

-^ A^ name^ •^ In actual

implementation name is replaced by a In^ actual

implementation

,^ name^

is^ replaced

by^ a

pointer

to^ its^ symbol

‐table^ entry

-^ A^ constant –^ A^ compiler–generated

temporary

Chapter^ 6:^ Intermediate

Code Generation^

CS5810^ Spring^

2009

Three

‐Address

Code

Instruction

and

ddAddress

-^ At most one operator on the right hand sideAt^ most

one^ operator

on^ the

right^

hand^

side L:^ t^ =^1

i+ i^ =^ t^1 *

do i = i + 1;

t^ =^ i *^2

t^ =^ a[t^3

] 2

f

do^ i^

i^ +^ 1; while

(a[i]^ <

v);

If^ t^ <^3

v^ goto L

Chapter^ 6:^ Intermediate

Code Generation^

CS5810^ Spring^

2009

QuadruplesQuadruples

A quadruple has 4 fields: op, arg1, arg2, result

minus

t^ =^ minus^1

c t^ b * t

c^

t^1

0 1 2 minus^3

t^ =^ b^ *^2

t^1 t^ =^ minus^3

c t^ b * t

*b c *

t^1

t^2 t^3

3 4 + 5

t^ =^ b^4

*^ t^3 t^ =^ t^5

+^ t^4 t

*^ b t^1

tt^3

4 tt^4

5

5 =

a^ =^ t^5

t^5

a

CS5810^ Spring^

2009

Chapter^ 6:^ Intermediate

Code Generation

Static Single

‐Assignment Form

Static

Single

Assignment

Form

-^ SSA is an IR that facilitate certain codeSSA

is^ an^

IR^ that

facilitate

certain

code

optimization^ –^ All^ assignments

are^ to

vars with

distinct

names

g p^ =^ a^

+^ b q^ p^

c

p^ =^ a^1

+^ b q^ p^

c

q^ =^ p^ ‐

c p^ =^ q *

d p = e^

p

q^ =^ p^11

‐^ c p^ =^ q^2

*^ d 1 p = e

p

p^ =^ e^

-^ p q =^ p +

q

p^ =^ e^3

-^ p^2 q^ =^ p^2

+^ q^3

Chapter^ 6:^ Intermediate

Code Generation^

CS5810^ Spring

2009

Static Single

‐Assignment Form

Static

Single

Assignment

Form

-^ What if the same variable is defined in twoWhat

if^ the

same

variable

is^ defined

in^ two

different

control

flow^

paths?^ if (flag)

if^ (flag)

x^ 1;

if^ (flag)

x^ =^ ‐1;^1 else

x^ =^ ‐1; else

x = 1;

else

x^ =^ 1;^2 x^ φ

(x^ x )

x^ =^ 1; y^ =^ x^ *

a;

x^ =^ φ^3

(x,x^1

y^ =^ x^3

*^ a;

Chapter^ 6:^ Intermediate

Code Generation^

CS5810^ Spring

2009