ARM assembly quicksort and recursion - gcc

Question

I'm trying to change C quick sort code to ARM assembly code.
Firstly, I apologize for my long question.
just in case, I wrote whole codes.
but only part that makes problem is function recursion part.
I almost done this work except funcion recursion part.
I've also tried converting C codes to ARM assembly with gcc cross compiler to see how compiler do. But there are still few things that I can't understand well.
This is C code.
void quicksort_c(int array[8],int first,int last)
{
int i, j, pivot, temp;
if(first < last)
{
pivot = first;
i = first;
j = last;
while(i < j)
{
while(array[i] <= array[pivot] && i < last)
{
i++;
}
while(array[j] > array[pivot])
{
j--;
}
if(i < j)
{
temp = array[i];
array[i] = array[j];
array[j] = temp;
}
}
temp = array[pivot];
array[pivot] = array[j];
array[j] = temp;
quicksort_c(array, first, j-1);
quicksort_c(array, j+1, last);
}
}
and this is arm assembly code that I wrote from scratch.
quicksort
STMFD sp!, {r0-r8,lr}
quicksort_recursion
CMP r1, r2 ;// if(first < last)
BGE out_of_if
outer_if
MOV r5, r1 ;// pivot = first
MOV r3, r1 ;// i = first;
MOV r4, r2 ;// j = last;
outer_while_loop
CMP r3, r4 ;// while(i < j)
BGE end_of_outer_while
outer_while
inner_while_1_loop
;//while(array[i] <= array[pivot] && i < last)
LDR r7, [r0, r3, lsl #2] ;//r7 = array[i]
LDR r8, [r0, r5, lsl #2] ;//r8 = array[pivot]
CMP r7, r8 ;//array[i] <= array[pivot]
BGT inner_while_2_loop
CMP r3, r2 ;// i < last
BGE inner_while_2_loop
inner_while_1
ADD r3, #1 ;//i++
B inner_while_1_loop
inner_while_2_loop
;//whlie(array[j] > array[pivot])
LDR r7, [r0, r4, lsl #2] ;// r7 = array[j]
LDR r8, [r0, r5, lsl #2] ;//r8 = array[pivot]
CMP r7, r8 ;// (array[j] > array[pivot])
BLE inner_if_cmp
inner_while_2
SUB r4, #1
B inner_while_2_loop
inner_if_cmp
CMP r3, r4;// if(i < j)
BGE outer_while_loop
inner_if
LDR r7, [r0, r3, lsl #2] ;// r7 = array[i]
MOV r6, r7 ;// temp = array[i]
LDR r8, [r0, r4, lsl #2] ;// r8 = array[j]
STR r8, [r0, r3, lsl #2] ;// array[i] = array[j]
STR r6, [r0, r4, lsl #2] ;// array[j] = temp;
B outer_while_loop
end_of_outer_while
LDR r7, [r0, r5, lsl #2] ;// r7 = array[pivot]
MOV r6, r7 ;// temp = array[pivot]
LDR r8, [r0, r4, lsl #2] ;// r8 = array[j]
STR r8, [r0, r5, lsl #2] ;// array[pivot] = array[j]
STR r6, [r0, r4, lsl #2] ;// array[j] = temp
;;//quicksort(array,first,j-1)
STMFD sp!, {r0-r8,lr}
SUBS r2, r4, #1
BL quicksort_recursion
;//LDMFD sp!, {r0-r8,pc}
;//quicksort(array, j+1, last)
STMFD sp!, {r0-r8,lr}
ADDS r1, r4, #1
BL quicksort_recursion
;//LDMFD sp!, {r0-r8,pc}
out_of_if
end_function
LDMFD sp!, {r0-r8,pc}
END
and this is how I use register
r0: array pointer
r1: first index
r2: last index
r3: i
r4: j
r5: pivot
r6: temp
r7: array[?] value
r8: array[?] value
I confirmed every parts except recursion of my code are work well.
At first, I did recursion in this way.
;;//quicksort(array,first,j-1)
SUBS r2, r4, #1
BL quicksort
;//quicksort(array, j+1, last)
ADDS r1, r4, #1
BL quicksort
but this code only do first function recursion.
ex)
Array before quicksorting : 5 1 4 7 8 3 6
Array after quicksorting : 1 2 4 3 5 8 7 6
I think it's because after function call, it doesn't go back to where it branched. so I added push and pop before and after function call like this.
;;//quicksort(array,first,j-1)
STMFD sp!, {r0-r8,lr}
SUBS r2, r4, #1
BL quicksort_recursion
;//quicksort(array, j+1, last)
STMFD sp!, {r0-r8,lr}
ADDS r1, r4, #1
BL quicksort_recursion
But this code falls in to infinite loop.
according to gcc compiled code,
quicksort_linux
cmp r1, r2
blt L16
bx lr
L16
push {r4, r5, r6, r7, r8, r9, r10, lr}
mov r10, r1
add ip, r0, r1, lsl #2
mov r5, r2
mov r4, r1
L3
lsls r3, r4, #2
add lr, r0, r3
ldr r7, [r0, r4, lsl #2]
ldr r6, [ip]
cmp r2, r4
ite le
movle r8, #0
movgt r8, #1
cmp r7, r6
it gt
movgt r8, #0
adds r3, r3, #4
add r3, r3, r0
cmp r8, #0
beq L9
L4
adds r4, r4, #1
mov lr, r3
ldr r7, [r3], #4
cmp r2, r4
ite le
movle r1, #0
movgt r1, #1
cmp r7, r6
it gt
movgt r1, #0
cmp r1, #0
bne L4
L9
lsls r3, r5, #2
add r9, r0, r3
ldr r1, [r0, r5, lsl #2]
cmp r1, r6
ble L5
subs r3, r3, #4
add r3, r3, r0
L6
subs r5, r5, #1
mov r9, r3
ldr r1, [r3], #-4
cmp r1, r6
bgt L6
L5
cmp r4, r5
bge L7
str r1, [lr]
str r7, [r9]
b L3
L7
mov r7, r2
mov r1, r10
mov r4, r0
ldr r3, [r0, r5, lsl #2]
str r3, [r0, r10, lsl #2]
str r6, [r0, r5, lsl #2]
subs r2, r5, #1
bl quicksort_linux
mov r2, r7
adds r1, r5, #1
mov r0, r4
bl quicksort_linux
pop {r4, r5, r6, r7, r8, r9, r10, pc}
END
It seems like they don't do any push or pop before or after branch but it works.
So, question is
1.what is problem of my function recursion code?
2.How can I fix that?
3.How can gcc compiled code works without any push and pop before and after function recursion?