Compilers Jakub Yaghob Computer skills Compilers Jakub Yaghob

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

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:

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:

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

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

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

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

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

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 = @A

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