c/x86

[ktye]

e.g. modified indexed assign

#include<stdint.h>
void f(int32_t *x, int32_t y, int32_t z) { x[y]+=z; }

// f vs g

int32_t *I;
#define    I32(x)   I[(x)>>2]
#define SetI32(x,y) I[(x)>>2]=(y)
void g(uint64_t x, int32_t y, int32_t z) {
        SetI32(((int32_t)(x)+(4*y)),(I32(((int32_t)(x)+(4*y)))+z));
}

with -O3

f:
        movsx   rsi, esi
        add     DWORD PTR [rdi+rsi*4], edx
        ret
g:
        lea     eax, [rdi+rsi*4]
        mov     ecx, edx
        mov     rdx, QWORD PTR I[rip]
        sar     eax, 2
        cdqe
        add     DWORD PTR [rdx+rax*4], ecx
        ret
I:
        .zero   8