With -O3

    .file   "main.c"
    .text
    .p2align 4,,15
    .globl  _xorBuffer
    .def    _xorBuffer; .scl    2;  .type   32; .endef
_xorBuffer:
LFB18:
    .cfi_startproc
    pushl   %ebp
    .cfi_def_cfa_offset 8
    .cfi_offset 5, -8
    pushl   %edi
    .cfi_def_cfa_offset 12
    .cfi_offset 7, -12
    pushl   %esi
    .cfi_def_cfa_offset 16
    .cfi_offset 6, -16
    pushl   %ebx
    .cfi_def_cfa_offset 20
    .cfi_offset 3, -20
    subl    $28, %esp
    .cfi_def_cfa_offset 48
    movl    56(%esp), %edx
    movl    48(%esp), %eax
    movl    52(%esp), %ecx
    testl   %edx, %edx
    je  L1
    movl    %edx, %ebx
    movl    %edx, 8(%esp)
    shrl    $4, %ebx
    movl    %ebx, %esi
    movl    %ebx, 4(%esp)
    sall    $4, %esi
    testl   %esi, %esi
    je  L3
    leal    16(%ecx), %edi
    cmpl    $15, %edx
    seta    15(%esp)
    cmpl    %edi, %eax
    leal    16(%eax), %ebp
    seta    %bl
    cmpl    %ebp, %ecx
    movl    %ebx, %edi
    seta    %bl
    movl    %ebx, %ebp
    orl %ebp, %edi
    movl    %edi, %ebx
    testb   %bl, 15(%esp)
    je  L3
    movl    4(%esp), %ebx
    xorl    %edi, %edi
    xorl    %ebp, %ebp
    .p2align 4,,10
L4:
    vmovdqu (%ecx,%edi), %xmm1
    addl    $1, %ebp
    vmovdqu (%eax,%edi), %xmm0
    vpxor   %xmm0, %xmm1, %xmm0
    vmovdqu %xmm0, (%eax,%edi)
    addl    $16, %edi
    cmpl    %ebp, %ebx
    ja  L4
    addl    %esi, %eax
    addl    %esi, %ecx
    subl    %esi, %edx
    cmpl    %esi, 8(%esp)
    je  L1
L3:
    xorl    %ebx, %ebx
    movl    %ecx, %esi
    .p2align 4,,10
L5:
    movzbl  (%esi,%ebx), %ecx
    xorb    %cl, (%eax,%ebx)
    addl    $1, %ebx
    subl    $1, %edx
    jne L5
L1:
    addl    $28, %esp
    .cfi_def_cfa_offset 20
    popl    %ebx
    .cfi_def_cfa_offset 16
    .cfi_restore 3
    popl    %esi
    .cfi_def_cfa_offset 12
    .cfi_restore 6
    popl    %edi
    .cfi_def_cfa_offset 8
    .cfi_restore 7
    popl    %ebp
    .cfi_def_cfa_offset 4
    .cfi_restore 5
    ret
    .cfi_endproc
LFE18:
    .def    ___main;    .scl    2;  .type   32; .endef
    .section .rdata,"dr"
LC0:
    .ascii "result = \0"
LC1:
    .ascii "%.2x\0"
    .section    .text.startup,"x"
    .p2align 4,,15
    .globl  _main
    .def    _main;  .scl    2;  .type   32; .endef
_main:
LFB19:
    .cfi_startproc
    pushl   %ebp
    .cfi_def_cfa_offset 8
    .cfi_offset 5, -8
    movl    %esp, %ebp
    .cfi_def_cfa_register 5
    pushl   %edi
    pushl   %esi
    pushl   %ebx
    andl    $-16, %esp
    subl    $48, %esp
    .cfi_offset 3, -20
    .cfi_offset 6, -16
    .cfi_offset 7, -12
    call    ___main
    movl    $32, (%esp)
    call    _malloc
    movl    $32, (%esp)
    movl    %eax, 44(%esp)
    call    _malloc
    movl    %eax, 40(%esp)
    movl    44(%esp), %eax
    movl    $-1431655766, (%eax)
    movl    $-1431655766, 4(%eax)
    movl    $-1431655766, 8(%eax)
    movl    $-1431655766, 12(%eax)
    movl    $-1431655766, 16(%eax)
    movl    $-1431655766, 20(%eax)
    movl    $-1431655766, 24(%eax)
    movl    $-1431655766, 28(%eax)
    movl    40(%esp), %eax
    movl    $-1145324613, (%eax)
    movl    $-1145324613, 4(%eax)
    movl    $-1145324613, 8(%eax)
    movl    $-1145324613, 12(%eax)
    movl    $-1145324613, 16(%eax)
    movl    $-1145324613, 20(%eax)
    movl    $-1145324613, 24(%eax)
    movl    $-1145324613, 28(%eax)
    movl    44(%esp), %eax
    negl    %eax
    andl    $15, %eax
    movl    %eax, 36(%esp)
    je  L17
    movl    %eax, %edi
    movl    40(%esp), %ecx
    xorl    %edx, %edx
    movl    44(%esp), %eax
    .p2align 4,,10
L11:
    movzbl  (%ecx), %esi
    addl    $1, %ecx
    movl    %esi, %ebx
    movl    $31, %esi
    xorb    %bl, (%eax)
    subl    %edx, %esi
    addl    $1, %edx
    addl    $1, %eax
    cmpl    %edx, %edi
    ja  L11
L10:
    movl    36(%esp), %edx
    movl    $32, 28(%esp)
    subl    %edx, 28(%esp)
    movl    28(%esp), %ebx
    shrl    $4, %ebx
    movl    %ebx, 24(%esp)
    sall    $4, %ebx
    testl   %ebx, %ebx
    movl    %ebx, 32(%esp)
    je  L12
    movl    40(%esp), %ebx
    movl    %eax, 36(%esp)
    movl    44(%esp), %edi
    movl    %ecx, 20(%esp)
    movl    24(%esp), %eax
    addl    %edx, %ebx
    movl    %ebx, 40(%esp)
    addl    %edx, %edi
    xorl    %ebx, %ebx
    movl    40(%esp), %ecx
    xorl    %edx, %edx
    .p2align 4,,10
L13:
    vmovdqu (%ecx,%edx), %xmm0
    addl    $1, %ebx
    vpxor   (%edi,%edx), %xmm0, %xmm0
    vmovdqa %xmm0, (%edi,%edx)
    addl    $16, %edx
    cmpl    %eax, %ebx
    jb  L13
    movl    36(%esp), %eax
    movl    20(%esp), %ecx
    movl    32(%esp), %edx
    subl    32(%esp), %esi
    addl    32(%esp), %eax
    addl    32(%esp), %ecx
    cmpl    %edx, 28(%esp)
    je  L14
L12:
    xorl    %edx, %edx
    .p2align 4,,10
L15:
    movzbl  (%ecx,%edx), %ebx
    xorb    %bl, (%eax,%edx)
    addl    $1, %edx
    cmpl    %esi, %edx
    jne L15
L14:
    movl    $LC0, (%esp)
    xorl    %ebx, %ebx
    call    _printf
    movl    44(%esp), %esi
    .p2align 4,,10
L16:
    movzbl  (%esi,%ebx), %eax
    movl    $LC1, (%esp)
    movl    %eax, 4(%esp)
    addl    $1, %ebx
    call    _printf
    cmpl    $32, %ebx
    jne L16
    movl    $10, (%esp)
    call    _putchar
    leal    -12(%ebp), %esp
    xorl    %eax, %eax
    popl    %ebx
    .cfi_remember_state
    .cfi_restore 3
    popl    %esi
    .cfi_restore 6
    popl    %edi
    .cfi_restore 7
    popl    %ebp
    .cfi_def_cfa 4, 4
    .cfi_restore 5
    ret
L17:
    .cfi_restore_state
    movl    40(%esp), %ecx
    movl    $32, %esi
    movl    44(%esp), %eax
    jmp L10
    .cfi_endproc
LFE19:
    .def    _putchar;   .scl    2;  .type   32; .endef
    .def    _malloc;    .scl    2;  .type   32; .endef
    .def    _printf;    .scl    2;  .type   32; .endef