Constant folding of array

array1.cpp

#include <cstdio>
  
const int a[] = {1, 2, 3, 4};

int func(int b[4]) {
  int sum = 0;
  for (int i = 0; i < 4; i++) {
    sum += a[i] * b[i];
  }
  return sum;
}

int main() {
  int b[] = {5, 6, 7, 8};
  printf("%d\n", func(b));
}

GCC and Clang can return an immediate value with -O3 -S.

main:
.LFB13:
  .cfi_startproc
  subq  $8, %rsp
  .cfi_def_cfa_offset 16
  movl  $70, %esi
  movl  $.LC1, %edi
  xorl  %eax, %eax
  call  printf
  xorl  %eax, %eax
  addq  $8, %rsp
  .cfi_def_cfa_offset 8
  ret