1. Compilers Jakub Yaghob
Computer skills
Compilers
Jakub Yaghob

2. Compiler Simplified definition
Translates a source code in an input language to a target code of a given CPU
program test;
var s,i:integer;
a:array[1..5] of integer;
begin
for i:=1 to 5 do
a[i]:=I;
s:=0;
s:=s+a[i];
writeln(s);
end.
compiler
.obj
linker
.exe

3. Control structures translation – if-then-else
if A<>B then S1 else S2
lw $t1,A($zero) lw $t2,B($zero) beq $t1,$t2,L1 S1 j L2 L1: S2 L2:

4. Control structures translation – while
while A<B do S1
L1: lw $t1,A($zero) lw $t2,B($zero) slt $t3,$t1,$t2 beq $t3,$zero,L2 S1 j L1 L2:

5. Control structures translation – repeat-until
repeat S1 until A<B
L1: S1 lw $t1,A($zero) lw $t2,B($zero) slt $t3,$t1,$t2 beq $t3,$zero,L1

6. Control structures translation – for
sw $r0,S($r0) li $r1,1 sw $r1,I($r0) j L2 L1: lw $r1,I($r0) subi $r2,$r1,1 sll $r2,$r2,2 lw $r2,arr($r2) lw $r3,S($r0) add $r3,$r3,$r2 sw $r3,S($r0) addi $r2,$r1,1 sw $r2,I($r0) L2: li $r3,5 bne $r1,$r3,L1
type int=integer; var arr:array[1..5] of int; s,i:int; begin …fill the array… s:=0; for i:=1 to 5 do s:=s+arr[i] end

7. Function calls Calling convention in procedural languages
Parameter passing
Returning a value from a function
Order of parameters evaluation
Stack cleanup
Stack frame pointer saving
Return address saving
Local variables
Register preservation

8. Function calls Call mechanism (C language)
Caller evaluates and stores actual parameters from right to left
Caller passes control flow using a “CALL” instruction
Callee saves return address on the stack
Callee saves caller’s frame pointer on the stack
Callee sets up its frame pointer
Callee saves some registers
Callee reserves space for local variables on the stack
Callee executes its code
Callee removes local variables from stack
Callee restores preserved registers
Callee restores caller’s frame pointer
Callee jumps to the return address
Caller removes parameters

9. Function calls – example
{ int a = f(1, 2); }
int f(int i, int j) { int r = i + j; return r; }
subi $sp,$sp,8
sw $ra,4($sp)
sw $fp,0($sp)
move $fp,$sp
subi $sp,$sp,4
lw $t8,8($fp)
lw $t9,12($fp)
add $t1,$t8,$t9
sw $t1,-4($fp)
lw $v0,-4($fp)
lw $ra,4($fp)
lw $fp,0($fp)
addi $sp,$sp,12
jr $ra
li $t8,2
subi $sp,$sp,4
sw $t8,0($sp)
li $t8,1
jal f
addi $sp,$sp,8
sw $v0,-4($fp) RA FP
R30 A
R29 J I RA FP R

10. Parameter passing Pass by value Pass by reference
The actual value of the parameter is copied as a local variable of the callee
Input parameter
Pass by reference
An address of the parameter is passed as local variable of the callee
Input/output parameters
procedure P(i:integer; var v:integer);
P(1, a); A
I = 1 V

11. Activation record (frame)
Control link
Activation record of the caller
Access link
Pointer to nonlocal data held in other activation records
Saved machine status
Return address to the code
Registers
Return value
Actual parameters
Control link
Access link
Saved machine status
Local data
Temporaries