Compiler Designs and Constructions

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Compiler Designs and Constructions

• Chapter 9 Translation
• Objectives
• Translation Method
• Three Address Code
• Dr. Mohsen Chitsaz

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Bottom-up evaluation of S-attributed

• Definitions
• Syntax-directed definition with only synthesized
  attributes is called S-attributed
• Use LR Parser
• Implementation
• Stack to hold info about subtrees that have been
  parsed

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• Example
• A.a F(X.x, Y.y, Z.z) for production
• A ---gt XYZ

lt--- Top
After Parse gt
Value of Symbol Table
Pointer to a State in LR(1) Parse Table
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• Example

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Cont.

• Using LR Parser Parse 3 5 4

lt--- Top Top 1 Top - 2
lt--- nTop

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(No Transcript)
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• Parse 3 5 4

L
E

Show Stack

T
E
F
T
F
T

4
F
5
3
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Intermediate Code Generation

• Type of intermediate code generation
• Graphical Representation
• a b c b c
• Syntax Tree

a


c
b
b
c
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• Dag

a

c
b
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• Advantages?
• Disadvantages?

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Representation of Syntax Tree
a-
lt--- b c
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• Using array

b c
b c
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• Postfix notation
• ( a ((b c) (b c)))
• a b c b c
• Advantages/Disadvantages?
• No need for ()
• No need for Temp
• Use Run-Time Stack
• Easy to reconstruct Parse Tree

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Three Address Code

• Three address Code
• General Form
• X A op B
• X, A, B are Const, Name, or Temp
• Example
• a b c d
• T0 b c
• T1 T0 d
• a T1

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Three Address Code

• Advantages?
• Disadvantages?

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Three Address Code

• Assignment
• Operand Operand1 op Operand2
• Unary Operation
• Operand Op Operand1
• Copy Statement
• Operand Operand1
• Procedure/Function Call
• Parm A,B
• Call P,n

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Three Address Code

• Indexed Assignment
• OperandI B
• Pointer
• A Address B
• Unconditional Jump
• GOTO L
• Conditional Jump
• If A RelOp B GOTO L

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Types of Three Address Codes

• Quadruples (Quad/Three Address Code)
• Record structure with 4 fields
• Arg1, Arg3, op, Result
• Example a -bcd

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Quadruples
Code U_Minus b T1 Mul c d T2 Add T1 T2 T3
Assign T3 a
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Types of Three Address Codes

• Triples (3 Tuples/Triplest)
• Record with 3 fields
• Arg1, Arg2, op
• Example a -b c d

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Triples

• Arg1, Arg2 are either a pointer to Symbol Table
  (Name, Constant) or a pointer to Triple Structure
• This is a Two Address Instruction
• Most Assembly Languages are made up of Triples

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• Indirect Tuples
• We use pointers to Triples
• Example a -b c d

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Indirect Tuples

• Save Space Why?
• Not good for optimizing code Why?
• Not good for memory assignment prior to code
  generation