The document discusses intermediate representations in compilers. It provides examples of intermediate representations at different levels, from high to low level. It also describes different types of intermediate representations like graphical and linear representations. Graphical representations include abstract syntax trees and control flow graphs, while linear representations include stack-based and triple code. Intermediate representations allow compilers to optimize code independently of the target machine and facilitate code improvements.

1. NADAR SARASWATHI COLLEGE OF ARTS AND SCIENCE

2.  Similar terms: Intermediate representation,
intermediate language
 Ties the front and back ends together
 Language and Machine neutral
 Many forms
 Level depends on how being processed
 More than one intermediate language may be
used by a compiler

3. Intermediate language levels
High
t1  a[i,j+2]
Medium
t1  j + 2
t2  i * 20
t3  t1 + t2
t4  4 * t3
t5  addr a
t6  t5 + t 4
t7  *t6
Low
r1 [fp-4]
r2  r1 + 2
r3  [fp-8]
r4  r3*20
r5  r4 + r2
r6  4 * r5
r7  fp – 216
f1  [r7+r6]

4. Intermediate Languages Types
 Graphical IRs: Abstract Syntax trees,
DAGs, Control Flow Graphs
 Linear IRs:
 Stack based (postfix)
 Three address code (quadruples)

5. ASTs and DAGs:
a := b *-c + b*-c
a +
* *
b - (uni)
c
a +
- (uni)
b b
*
- (uni)
c c
:=
:=

6. • If a compiler translates the source language to its target machine language without
having the option for generating intermediate code, then for each new machine, a full native
compiler is required.
 Intermediate code eliminates the need of a new full compiler for every unique machine by
keeping the analysis portion same for all the compilers.
 The second part of compiler, synthesis, is changed according to the target machine.
 It becomes easier to apply the source code modifications to improve code performance by
applying code optimization techniques on the intermediate code.

7. Intermediate Representation
Intermediate codes can be represented in a variety of ways and they have their own
benefits.
•High Level IR - High-level intermediate code representation is very close to the source
language itself. They can be easily generated from the source code and we can easily
apply code modifications to enhance performance. But for target machine optimization, it
is less preferred.
•Low Level IR - This one is close to the target machine, which makes it suitable for
register and memory allocation, instruction set selection, etc. It is good for machine-
dependent optimizations.

8. Semantic Rule Program fragment
E.code = E1.code || E2.code ||
op
print op
E.code = E1.code
E.code = id print id
Example
Production
1.E → E1 op E2
2.E → (E1)
3.E → id

9. Parsetree

10. A sentence id + id * id would have the following syntax tree:

11. Thank you