Code demonstrating the use of the `restrict` keyword

restrict-demonstration.c

#include <string.h>

void simple_string_copy_without_restrict(char *destination, char const *source) {
    for (unsigned int i = 0; i <= strlen(source); i++) {
        destination[i] = source[i];
    }
}

void simple_string_copy_with_restrict(char *restrict destination, char const *restrict source) {
    for (unsigned int i = 0; i <= strlen(source); i++) {
        destination[i] = source[i];
    }
}

restrict-demonstration_arm64.asm

simple_string_copy_without_restrict:
        stp     x29, x30, [sp, -48]!
        mov     x29, sp
        stp     x19, x20, [sp, 16]
        stp     x21, x22, [sp, 32]
        mov     x22, x0
        mov     x21, x1
        mov     w19, 0
        b       .L2
.L3:
        ldrb    w1, [x21, w19, uxtw]
        strb    w1, [x22, w19, uxtw]
        add     w19, w19, 1
.L2:
        uxtw    x20, w19
        mov     x0, x21
        bl      strlen
        cmp     x20, x0
        bls     .L3
        ldp     x19, x20, [sp, 16]
        ldp     x21, x22, [sp, 32]
        ldp     x29, x30, [sp], 48
        ret
simple_string_copy_with_restrict:
        stp     x29, x30, [sp, -48]!
        mov     x29, sp
        stp     x19, x20, [sp, 16]
        stp     x21, x22, [sp, 32]
        mov     x22, x0
        mov     x21, x1
        mov     w19, 0
        b       .L6
.L7:
        ldrb    w1, [x21, w19, uxtw]
        strb    w1, [x22, w19, uxtw]
        add     w19, w19, 1
.L6:
        uxtw    x20, w19
        mov     x0, x21
        bl      strlen
        cmp     x20, x0
        bls     .L7
        ldp     x19, x20, [sp, 16]
        ldp     x21, x22, [sp, 32]
        ldp     x29, x30, [sp], 48
        ret

restrict-demonstration_x86-64.asm

simple_string_copy_without_restrict:
        pushq   %r13
        pushq   %r12
        pushq   %rbp
        pushq   %rbx
        subq    $8, %rsp
        movq    %rdi, %r13
        movq    %rsi, %r12
        movl    $0, %ebp
        jmp     .L2
.L3:
        movzbl  (%r12,%rbx), %eax
        movb    %al, 0(%r13,%rbx)
        addl    $1, %ebp
.L2:
        movl    %ebp, %ebx
        movq    %r12, %rdi
        call    strlen
        cmpq    %rbx, %rax
        jnb     .L3
        addq    $8, %rsp
        popq    %rbx
        popq    %rbp
        popq    %r12
        popq    %r13
        ret
simple_string_copy_with_restrict:
        pushq   %r13
        pushq   %r12
        pushq   %rbp
        pushq   %rbx
        subq    $8, %rsp
        movq    %rdi, %r13
        movq    %rsi, %r12
        movl    $0, %ebp
        jmp     .L6
.L7:
        movzbl  (%r12,%rbx), %eax
        movb    %al, 0(%r13,%rbx)
        addl    $1, %ebp
.L6:
        movl    %ebp, %ebx
        movq    %r12, %rdi
        call    strlen
        cmpq    %rbx, %rax
        jnb     .L7
        addq    $8, %rsp
        popq    %rbx
        popq    %rbp
        popq    %r12
        popq    %r13
        ret