Semantics

1
Semantics

• CS 236 - Lecture 11
• West Virginia University
• February 17, 2000
• Frances L. Van Scoy
• fvanscoy_at_wvu.edu

2
Overview

• Intermediate Code
• Examples of Intermediate Code Generated from
  Program Fragments

3
Intermediate Code

• generated by Intermediate Code Generator
• is a notation intermediate in complexity between
  high level programming language and assembly
  language

4
Some Forms of Intermediate Code

• post fix notation
• trees
• triples
• quadruples

5
Post fix notation examples

• x a - b c d
• x a b c - d
• x a b - c d
• x a b c d -

6
Syntax tree examples
x a - b c d
x a b - c d


x
-
x



-
d
a
b
c
d
a

c
b
7
Triple examples

• x a - b c d
• (1) (, b, c)
• (2) (-, a, (1))
• (3) (, (2), d)
• (4) (, (3), x)

• x a b - c d
• (1) (, a, b)
• (2) (, c, d)
• (3) (-, (1), (2))
• (4) (, (3), x)

8
Quadruple examples

• x a - b c d
• (1) (, b, c, temp1)
• (2) (-, a, temp1, temp2)
• (3) (, temp2, d)
• (4) (, temp3, -, x)

• x a b - c d
• (1) (, a, b, temp1)
• (2) (, c, d, temp2)
• (3) (-, temp1, temp2, temp3)
• (4) (, temp3, -, x)

9
Quadruples from If Statement

• if x gt y then w a else w b
• using absolute quadruple numbers
• (1) (-,x,y,temp1)
• (2) (gt0,temp1,Q3,Q5)
• (3) (,a,-,w)
• (4) (goto,-,-,Q6)
• (5) (,b,-,q)
• (6) . . .

• using relative quadruple labels
• (1) (-,x,y,temp1)
• (2) (gt0,temp1,L1,L2)
• (3) (label,-,-,L1)
• (4) (,a,-,w)
• (5) (goto,-,-,L3)
• (6) (label,-,-,L2)
• (7) (,b,-,q)
• (8) (label,-,-,L3)

10
Quadruples from While statement

• while x gt y loop z z 3
• using absolute quadruple numbers
• (1) (-,x,y,temp1)
• (2) (gt0,temp1,Q3,Q5)
• (3) (,z,3,temp2)
• (4) (,temp2,-,z)
• (4) (goto,-,-,Q1)
• (5) . . .

• using relative quadruple labels
• (1) (label,-,-,L1)
• (1) (-,x,y,temp1)
• (2) (gt0,temp1,L2,L3)
• (3) (label,-,-,L2)
• (4) (,z,3,temp2)
• (5) (,temp2,-,z)
• (6) (goto,-,-,L1)
• (7) (label,-,-,L3)
• (8) (label,-,-,L3)

11
Quadruples from Procedure or Function Calls

• assume procedure P(x,y)
• and procedure Q(a,b,c).
• P(10,result)
• (1) (param,-,-,10)
• (2) (param,-,-,result)
• (3) (call,P,2,-)
• Q(x,y,z)
• (1) (param,-,-,x)
• (2) (param,-,-,y)
• (3) (param,-,-,z)
• (4) call (Q,3,-)

• assume function f(x,y) and function g(a,b,c)
• z g(10n,f(p,q),w)
• (1) (,10,n,temp1)
• (2) (param,-,-,temp1)
• (3) (param,-,-,p)
• (4) (param,-,-,q)
• (5) (call,F,2,temp2)
• (6) (param,-,-,temp2)
• (7) (param,-,-,w)
• (8) (call,g,3,temp3)
• (9) (,temp3,-,z)

12
Summary
13
Quiz