This document discusses intermediate code in compilers. It begins by describing the stages of a compiler from source code to intermediate code to machine code. It then provides an example of translating a simple C program to intermediate code. The remainder of the document describes aspects of a simple virtual machine that can execute intermediate code, including instructions like LIT, LOD, STO, and OPR, and an example of intermediate code generated for a small C program.

1. CSE340 - Principles of
Programming Languages
Lecture 20:
Intermediate Code I
Javier Gonzalez-Sanchez
BYENG M1-38
Office Hours: By appointment

2. Javier Gonzalez-Sanchez | CSE340 | Summer 2015 | 2
A Compiler in Action
Lexer
Parser
Semantic
Analyzer
Code
Generation
Words
Tokens
Sentences
Symbol table
Uniqueness
Type matching
Translation
Source Code è Intermediate Code
Intermediate Code è Machine or Binary Code
Analysis
Compilation
Assembly

3. Javier Gonzalez-Sanchez | CSE340 | Summer 2015 | 3
Source Code
{
int a;
int b;
int c;
int d;
if (a != 5) {
b = c + d;
}
print (a);
}

4. Javier Gonzalez-Sanchez | CSE340 | Summer 2015 | 4
Intermediate (Object) Code
a,int,global 0
b,int,global 0
c,int,global 0
d,int,global 0
#E1,int,label,9
#P,int,label,1
@
lod a, 0
lit 5, 0
opr 14, 0
jmc #e1, false
lod c, 0
lod d, 0
opr 2, 0
sto b, 0
lod a, 0
opr 21, 0
opr 1, 0
Symbol table
Instructions

5. Javier Gonzalez-Sanchez | CSE340 | Summer 2015 | 5
Translate Source to Object
{
int a;
int b;
int c;
int d;
if (a != 5) {
b = c + d;
}
print (a);
}
a,int,global 0
b,int,global 0
c,int,global 0
d,int,global 0
#E1,int,label,9
#P,int,label,1
@
lod , 0
lit 5, 0
opr 14, 0
jmc #e1, false
lod c, 0
lod d, 0
opr 2, 0
sto b, 0
lod a, 0
opr 21, 0
opr 1, 0

6. Javier Gonzalez-Sanchez | CSE340 | Summer 2015 | 6
High-Level Languages
X,E,G,O,O
#e1,I,I,0,7
@
OPR 19, AX
STO x, AX
LIT 5, AX
OPR 21, AX
LOD #e1,AX
CAL 1, AX
OPR 0, AX
5
Virtual Machine
(interpreter)
// sorce code
int x;
int foo () {
read (x);
print (5);
}
main () {
foo ();
}
Lexer
Parser
Semantic Analyzer
Code Generation
01001010101000010
01010100101010010
10100100000011011
11010010110101111
00010010101010010
10101001010101011
Assembler
compilation execution

7. Javier Gonzalez-Sanchez | CSE340 | Summer 2015 | 7
High-Level Languages
X,E,G,O,O
#e1,I,I,0,7
@
OPR 19, AX
STO x, AX
LIT 5, AX
OPR 21, AX
LOD #e1,AX
CAL 1, AX
OPR 0, AX
5
Virtual Machine
(interpreter)
// sorce code
int x;
int foo () {
read (x);
print (5);
}
main () {
foo ();
}
Lexer
Parser
Semantic Analyzer
Code Generation
01001010101000010
01010100101010010
10100100000011011
11010010110101111
00010010101010010
10101001010101011
Assembler
compilation execution

8. Javier Gonzalez-Sanchez | CSE340 | Summer 2015 | 8
A Simple Virtual Machine
CPU
ALU
Register
Memory

9. Javier Gonzalez-Sanchez | CSE340 | Summer 2015 | 9
Memory
program
A Simple Virtual Machine
CPU
ALU
Register
Code
sto 0, s
sto 0, d
sto 0, c
sto 0, d
lod s, 0
lit “s”, 0
opr 14, 0
jmc #a1, false
lod b, 0
Symbol
Table

10. Javier Gonzalez-Sanchez | CSE340 | Summer 2015 | 10
A Simple Virtual Machine
CPU
ALU
Register
PC
Memory
program
Code
sto 0, s
sto 0, d
sto 0, c
sto 0, d
lod s, 0
lit “s”, 0
opr 14, 0
jmc #a1, false
lod b, 0
Symbol
Table

11. Javier Gonzalez-Sanchez | CSE340 | Summer 2015 | 11
Instructions
instruction first second
parameter parameter

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Instructions
• LIT <value>, <register_id>
Put a constant value in a CPU register
Examples:
LIT 5, 0
LIT 5.5, 0
LIT 'a', 0
LIT ”hello”, 0
LIT true, 0

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Instructions
• LOD <variable>, <register_id>
Search for <variable> in the symbol table
Read its value
Put the value of <variable> in the CPU register
Examples:
LOD a, 0
LOD hello, 0
LOD cse340, 0

14. Javier Gonzalez-Sanchez | CSE340 | Summer 2015 | 14
Instructions
• STO <variable>, <register_id>
Read a value from the CPU register
Search for <variable> in the symbol table
Store the value into the variable
Examples:
STO a, 0
STO hello, 0
STO cse340, 0

15. Javier Gonzalez-Sanchez | CSE340 | Summer 2015 | 15
Example
Source Code:
{
int a; int b;
a = 10;
b = a;
Symbol Table:
Type Name Scope Value
int a global 0
int b global 0
Intermediate (Object) Code:
LIT 10,0
STO a,0
LOD a,0
STO b,0

16. Javier Gonzalez-Sanchez | CSE340 | Summer 2015 | 16
Instructions
• OPR <operation>, <register_id>
Read one or two values from the CPU register
Do the operation <operation>
Put the result into the CPU register
Examples:
OPR 1, 0 ; return
OPR 2, 0 ; add
OPR 3, 0 ; subtract

17. Javier Gonzalez-Sanchez | CSE340 | Summer 2015 | 17
Operations
Number Action
0 Exit program
1 Return
2 ADD: POP A, POP B, PUSH B+A
3 SUBTRACT: POP A, POP B, PUSH B-A
4 MULTIPLY: POP A, POP B, PUSH B*A
5 DIVIDE: POP A, POP B, PUSH B/A
6 MOD: POP A, POP B, PUSH (B mod A)
7 POW: POP A, POP B, PUSH (A to the power B)
8 OR: POP A, POP B, PUSH (B or A)
9 AND: POP A, POP B, PUSH (B and A)
10 NOT: POP A, PUSH (not A)
11 TEST GREATER THAN: POP A, POP B, PUSH (B>A)
12 TEST LESS THAN: POP A, POP B, PUSH (B<A)
13 TEST GREATER THAN OR EQUAL: POP A, POP B, PUSH (B>=A)

18. Javier Gonzalez-Sanchez | CSE340 | Summer 2015 | 18
Operations
Number Action
14 TEST LESS THAN OR EQUAL: POP A, POP B, PUSH (B<=A)
15 TEST EQUAL: POP A, POP B, PUSH (B=A)
16 TEST NOT EQUAL: POP A, POP B, PUSH (B<>A)
17
18 clear screen
19 read a value from the standard input
20 print a value to the standard output
21 print a value to the standard output and a newline character

19. Javier Gonzalez-Sanchez | CSE340 | Summer 2015 | 19
Example
{
int a;
int b;
a = 10;
b = a;
a = a * 10;
b = 2 + 3 + 4;
}
Type Name Scope Value
int a global 0
int b global 0
LIT 10, 0
STO a, 0
LOD a, 0
STO b, 0
LOD a, 0
LIT 10, 0
OPR 4, 0 ; multiply
STO a, 0
LIT 2, 0
LIT 3, 0
OPR 2, 0 ; add
LIT 4, 0
OPR 2, 0 ; add
STO b, 0
OPR 1,0
OPR 0,0

20. Javier Gonzalez-Sanchez | CSE340 | Summer 2015 | 20
to be continued...

21. CSE340 - Principles of Programming Languages
Javier Gonzalez-Sanchez
javiergs@asu.edu
Summer 2015
Disclaimer. These slides can only be used as study material for the class CSE340 at ASU. They cannot be distributed or used for another purpose.