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Swap variable with and without helper variable - which is faster?

I think you have all heard of the "exchange problem"; SO is full of questions about this. A swap version without using a third variable is often considered faster, since you have one less variable. I wanted to know what was going on behind the curtains, and wrote the following two programs:

int main () {
    int a = 9;
    int b = 5;
    int swap;

    swap = a;
    a = b;
    b = swap;

    return 0;
}

and the version without the third variable:

int main () {
    int a = 9;
    int b = 5;

    a ^= b;
    b ^= a;
    a ^= b;

    return 0;
}

I generated the build code using clang and got this for the first version (which uses the third variable):

...
Ltmp0:
    movq   %rsp, %rbp
Ltmp1:
    movl   $0, %eax
    movl   $0, -4(%rbp)
    movl   $9, -8(%rbp)
    movl   $5, -12(%rbp)
    movl   -8(%rbp), %ecx
    movl   %ecx, -16(%rbp)
    movl   -12(%rbp), %ecx
    movl   %ecx, -8(%rbp)
    movl   -16(%rbp), %ecx
    movl   %ecx, -12(%rbp)
    popq   %rbp
    ret
Leh_func_end0:
...

and this is for the second version (which does not use the third variable):

...
Ltmp0:
    movq    %rsp, %rbp
Ltmp1:
    movl   $0, %eax
    movl   $0, -4(%rbp)
    movl   $9, -8(%rbp)
    movl   $5, -12(%rbp)
    movl   -12(%rbp), %ecx
    movl   -8(%rbp), %edx
    xorl   %ecx, %edx
    movl   %edx, -8(%rbp)
    movl   -8(%rbp), %ecx
    movl   -12(%rbp), %edx
    xorl   %ecx, %edx
    movl   %edx, -12(%rbp)
    movl   -12(%rbp), %ecx
    movl   -8(%rbp), %edx
    xorl   %ecx, %edx
    movl   %edx, -8(%rbp)
    popq   %rbp
    ret
Leh_func_end0:
...

The second option is longer, but I know little about assembler, so I have no idea if this means that it is slower, so I would like to hear the opinion of someone more knowledgeable about this.

swap ?

+5
3

.

void swap_temp(int *restrict a, int *restrict b){
    int temp = *a;
    *a = *b;
    *b = temp;
}

void swap_xor(int *restrict a, int *restrict b){
    *a ^= *b;
    *b ^= *a;
    *a ^= *b;
}

gcc -O3 -std=c99 -S -o swapping.s swapping.c

    .file   "swapping.c"
.text
.p2align 4,,15
.globl swap_temp
.type   swap_temp, @function
swap_temp:
.LFB0:
.cfi_startproc
movl    (%rdi), %eax
movl    (%rsi), %edx
movl    %edx, (%rdi)
movl    %eax, (%rsi)
ret
.cfi_endproc
.LFE0:
.size   swap_temp, .-swap_temp
.p2align 4,,15
.globl swap_xor
.type   swap_xor, @function
swap_xor:
.LFB1:
.cfi_startproc
movl    (%rsi), %edx
movl    (%rdi), %eax
xorl    %edx, %eax
xorl    %eax, %edx
xorl    %edx, %eax
movl    %edx, (%rsi)
movl    %eax, (%rdi)
ret
.cfi_endproc
.LFE1:
.size   swap_xor, .-swap_xor
.ident  "GCC: (SUSE Linux) 4.5.1 20101208 [gcc-4_5-branch revision 167585]"
.section    .comment.SUSE.OPTs,"MS",@progbits,1
.string "Ospwg"
.section    .note.GNU-stack,"",@progbits

swap_temp , .

+7

XOR , . , . XCHG, , , 3 MOVs - . temp - ;)

+2

, , , , .

movl   -12(%rbp), %ecx

- ecx, rbp, (-12) ( 3) , ecx, , -12 (% rbp).

, , , , .

0

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