Intermediate Language
COP-3402

SimpleIR

Our intermediate representation.

Example: C program

int main(int argc, char **argv) {
  int x;
  int retval;
  x = read_int();
  retval = print_int(x);
  return 0;
}

Example: SimpleIR

function main
localvars argc argv x retval
params argc argv
x := call read_int
x := x * 2
retval := call print_int x
return 0

Compilation units

One file is one compilation
One compilation unit defines one function

Minimum SimpleIR

function main
return 0

function and return must appear in each SimpleIR program
Function takes a single name
Return takes an integer literal or a variable name

Defines a new function called main.

With parameters

function main
localvars argc argv x y
params argc argv
# instructions go here
return 0

localvars declares all variable, including parameters
params are a subset of localvars

For instance, in C, parameters to the function are local variables. In SimpleIR you need to declare all local variables first, include all parameters. Then specify separately which local variables are the parameters.

Statements

Assignment

x := 2
y := x

Sets the value of a variable to
Use the := symbol
Assignment to either
- an to integer literal or
- another variable name

Arithmetic

x := x + 2

A single operation, no arithmetic expressions
Always assigns the result to a variable name

Function calls

x := call print_int x

Works like a C function call
No parentheses
List arguments after the function name

Branching

ifgoto x > 0 goto end
x = x * -1
end:

No structured code, more like assembly
goto for unconditional branches, ifgoto for conditional
Define labels as targets of branching

Pointers

t1 := &x
t2 := *t1
*t1 := 11

Ampersand gets address
t2 := *t1 dereferences t1 and gets its value
*t1 dereferences t1 and assigns its value

Example program: exponents

function exponent
localvars base exp result
params base exp
result = 1
top:
if exp <= 0 goto end
result = result * base
exp = exp - 1
goto top
end:
return result

SimpleIR Grammar

grammar SimpleIR;

unit: function;

function: 'function' NAME localvars? params? statement* return;

localvars: 'localvars' NAME+;

params: 'params' NAME+;

return: 'return' operand=(NAME | NUM);

statement: assign | deref | ref | assignderef | operation | call | label | goto | ifgoto;

operation: NAME ':=' operand1=(NAME | NUM) operator=('+' | '-' | '*' | '/' | '%') operand2=(NAME | NUM);

assign: NAME ':=' operand=(NAME | NUM);

deref: NAME ':=' '*' NAME;

ref: NAME ':=' '&' NAME;

assignderef: '*' NAME ':=' operand=(NAME | NUM);

call: NAME ':=' 'call' NAME NAME*;

label: NAME ':';

goto: 'goto' NAME;

ifgoto: 'if' operand1=(NAME | NUM) operator=('=' | '!=' | '<' | '<=' | '>' | '>=') operand2=(NAME | NUM) 'goto' labelname=NAME;

NAME: [a-zA-Z_] ([a-zA-Z_] | [0-9])* ;
NUM: [0-9]+ ;

PLUS: '+' ;
MINUS: '-' ;
STAR: '*' ;
SLASH: '/' ;
PERCENT: '%' ;

EQ: '=' ;
NEQ: '!=' ;
LT: '<' ;
LTE: '<=' ;
GT: '>' ;
GTE: '>=' ;

WS:   [ \t\r\n]+ -> skip ;

Intermediate Language COP-3402