Well-known function. What does it compute? Why does the stack overflow if 4 and 2 are supplied at input? Is there any error?
m$ = 48
n$ = 56
f PROC
$LN14:
push rbx
sub rsp, 32
mov eax, edx
mov ebx, ecx
test ecx, ecx
je SHORT $LN11@f
$LL5@f:
test eax, eax
jne SHORT $LN1@f
mov eax, 1
jmp SHORT $LN12@f
$LN1@f:
lea edx, DWORD PTR [rax-1]
mov ecx, ebx
call f
$LN12@f:
dec ebx
test ebx, ebx
jne SHORT $LL5@f
$LN11@f:
inc eax
add rsp, 32
pop rbx
ret 0
f ENDP
f PROC
PUSH {r4,lr}
MOVS r4,r0
ADDEQ r0,r1,#1
POPEQ {r4,pc}
CMP r1,#0
MOVEQ r1,#1
SUBEQ r0,r0,#1
BEQ |L0.48|
SUB r1,r1,#1
BL f
MOV r1,r0
SUB r0,r4,#1
|L0.48|
POP {r4,lr}
B f
ENDP
f PROC
PUSH {r4,lr}
MOVS r4,r0
BEQ |L0.26|
CMP r1,#0
BEQ |L0.30|
SUBS r1,r1,#1
BL f
MOVS r1,r0
|L0.18|
SUBS r0,r4,#1
BL f
POP {r4,pc}
|L0.26|
ADDS r0,r1,#1
POP {r4,pc}
|L0.30|
MOVS r1,#1
B |L0.18|
ENDP
f:
stp x29, x30, [sp, -48]!
add x29, sp, 0
str x19, [sp,16]
str w0, [x29,44]
str w1, [x29,40]
ldr w0, [x29,44]
cmp w0, wzr
bne .L2
ldr w0, [x29,40]
add w0, w0, 1
b .L3
.L2:
ldr w0, [x29,40]
cmp w0, wzr
bne .L4
ldr w0, [x29,44]
sub w0, w0, #1
mov w1, 1
bl f
b .L3
.L4:
ldr w0, [x29,44]
sub w19, w0, #1
ldr w0, [x29,40]
sub w1, w0, #1
ldr w0, [x29,44]
bl f
mov w1, w0
mov w0, w19
bl f
.L3:
ldr x19, [sp,16]
ldp x29, x30, [sp], 48
ret
Optimizing GCC generates a lot more code. Why?
f:
stp x29, x30, [sp, -160]!
add x29, sp, 0
stp d8, d9, [sp,96]
stp x19, x20, [sp,16]
stp d10, d11, [sp,112]
stp x21, x22, [sp,32]
stp d12, d13, [sp,128]
stp x23, x24, [sp,48]
stp d14, d15, [sp,144]
stp x25, x26, [sp,64]
stp x27, x28, [sp,80]
cbz w0, .L2
sub w0, w0, #1
fmov s10, w0
b .L4
.L46:
fmov w0, s10
mov w1, 1
sub w0, w0, #1
fmov s10, w0
fmov w0, s13
cbz w0, .L2
.L4:
fmov s13, s10
cbz w1, .L46
sub w1, w1, #1
fmov s11, s10
b .L7
.L48:
fmov w0, s11
mov w1, 1
sub w0, w0, #1
fmov s11, w0
fmov w0, s14
cbz w0, .L47
.L7:
fmov s14, s11
cbz w1, .L48
sub w1, w1, #1
fmov s12, s11
b .L10
.L50:
fmov w0, s12
mov w1, 1
sub w0, w0, #1
fmov s12, w0
fmov w0, s15
cbz w0, .L49
.L10:
fmov s15, s12
cbz w1, .L50
sub w1, w1, #1
fmov s8, s12
b .L13
.L52:
fmov w0, s8
mov w1, 1
sub w0, w0, #1
fmov s8, w0
fmov w0, s9
cbz w0, .L51
.L13:
fmov s9, s8
cbz w1, .L52
sub w1, w1, #1
fmov w22, s8
b .L16
.L54:
mov w1, 1
sub w22, w22, #1
cbz w28, .L53
.L16:
mov w28, w22
cbz w1, .L54
sub w1, w1, #1
mov w21, w22
b .L19
.L56:
mov w1, 1
sub w21, w21, #1
cbz w24, .L55
.L19:
mov w24, w21
cbz w1, .L56
sub w1, w1, #1
mov w20, w21
b .L22
.L58:
mov w1, 1
sub w20, w20, #1
cbz w25, .L57
.L22:
mov w25, w20
cbz w1, .L58
sub w1, w1, #1
mov w26, w20
b .L25
.L60:
mov w1, 1
sub w26, w26, #1
cbz w27, .L59
.L25:
mov w27, w26
cbz w1, .L60
sub w1, w1, #1
mov w19, w26
b .L28
.L62:
mov w23, w19
mov w1, 1
sub w19, w19, #1
cbz w23, .L61
.L28:
add w0, w19, 1
cbz w1, .L62
sub w1, w1, #1
mov w23, w19
sub w19, w19, #1
bl f
mov w1, w0
cbnz w23, .L28
.L61:
add w1, w1, 1
sub w26, w26, #1
cbnz w27, .L25
.L59:
add w1, w1, 1
sub w20, w20, #1
cbnz w25, .L22
.L57:
add w1, w1, 1
sub w21, w21, #1
cbnz w24, .L19
.L55:
add w1, w1, 1
sub w22, w22, #1
cbnz w28, .L16
.L53:
fmov w0, s8
add w1, w1, 1
sub w0, w0, #1
fmov s8, w0
fmov w0, s9
cbnz w0, .L13
.L51:
fmov w0, s12
add w1, w1, 1
sub w0, w0, #1
fmov s12, w0
fmov w0, s15
cbnz w0, .L10
.L49:
fmov w0, s11
add w1, w1, 1
sub w0, w0, #1
fmov s11, w0
fmov w0, s14
cbnz w0, .L7
.L47:
fmov w0, s10
add w1, w1, 1
sub w0, w0, #1
fmov s10, w0
fmov w0, s13
cbnz w0, .L4
.L2:
add w0, w1, 1
ldp d8, d9, [sp,96]
ldp x19, x20, [sp,16]
ldp d10, d11, [sp,112]
ldp x21, x22, [sp,32]
ldp d12, d13, [sp,128]
ldp x23, x24, [sp,48]
ldp d14, d15, [sp,144]
ldp x25, x26, [sp,64]
ldp x27, x28, [sp,80]
ldp x29, x30, [sp], 160
ret
f: # CODE XREF: f+64
# f+94 ...
var_C = -0xC
var_8 = -8
var_4 = -4
arg_0 = 0
arg_4 = 4
addiu $sp, -0x28
sw $ra, 0x28+var_4($sp)
sw $fp, 0x28+var_8($sp)
sw $s0, 0x28+var_C($sp)
move $fp, $sp
sw $a0, 0x28+arg_0($fp)
sw $a1, 0x28+arg_4($fp)
lw $v0, 0x28+arg_0($fp)
or $at, $zero
bnez $v0, loc_40
or $at, $zero
lw $v0, 0x28+arg_4($fp)
or $at, $zero
addiu $v0, 1
b loc_AC
or $at, $zero
loc_40: # CODE XREF: f+24
lw $v0, 0x28+arg_4($fp)
or $at, $zero
bnez $v0, loc_74
or $at, $zero
lw $v0, 0x28+arg_0($fp)
or $at, $zero
addiu $v0, -1
move $a0, $v0
li $a1, 1
jal f
or $at, $zero
b loc_AC
or $at, $zero
loc_74: # CODE XREF: f+48
lw $v0, 0x28+arg_0($fp)
or $at, $zero
addiu $s0, $v0, -1
lw $v0, 0x28+arg_4($fp)
or $at, $zero
addiu $v0, -1
lw $a0, 0x28+arg_0($fp)
move $a1, $v0
jal f
or $at, $zero
move $a0, $s0
move $a1, $v0
jal f
or $at, $zero
loc_AC: # CODE XREF: f+38
# f+6C
move $sp, $fp
lw $ra, 0x28+var_4($sp)
lw $fp, 0x28+var_8($sp)
lw $s0, 0x28+var_C($sp)
addiu $sp, 0x28
jr $ra
or $at, $zero
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