[C++23] I want `[[assume(p1 != p2)]]` can be optimized as __restrict

[SekaiArendelle]

source code:

int f(int *a, int *__restrict b) noexcept {
    *a = 1;
    *b = 2;
    return *a + *b;
}

int f2(int *a, int *b) noexcept {
    [[assume(a != b)]];
    *a = 1;
    *b = 2;
    return *a + *b;
}

output:

f(int*, int*):
        mov     dword ptr [rdi], 1
        mov     dword ptr [rsi], 2
        mov     eax, 3
        ret

f2(int*, int*):
        mov     dword ptr [rdi], 1
        mov     dword ptr [rsi], 2
        mov     eax, dword ptr [rdi]
        add     eax, 2
        ret

compile with -std=c++23 -O3

[dtcxzyw]

IIUC a != b cannot imply that the load of *a does not alias with the store *b = 2 (e.g., static_cast<char*>(a) == static_cast<char*>(b) + 2 on some platforms which allow unaligned memory access).

Instead, you can use __builtin_assume_separate_storage to improve alias analysis: https://godbolt.org/z/d88o6afGT