sample of alignas

test2.cpp

#include <iostream>

struct myv4df{
  alignas(32) double v[4];
};

void
func(myv4df &a, myv4df &b){
  for(int i=0;i<4;i++){
    a.v[i] += b.v[i];
  }
}

int
main(int argc, char**argv){
  double d1 = atof(argv[1]);
  double d2 = atof(argv[2]);
  myv4df a,b;
  for(int i=0;i<4;i++){
    a.v[i] = d1;
    b.v[i] = d2;
  }
  func(a,b);
  for(int i=0;i<4;i++){
    printf("%f\n",a.v[i]);
  }
}

test2.s

#       strtod(const char *, char **)     
# double d1 = atof(argv[1]);をやってるところ
        call      strtod                                        #16.15
                                # LOE rbx r12 r13 r14 r15 xmm0
..B1.10:                        # Preds ..B1.11
        vmovsd    %xmm0, 32(%rsp)                               #16.15
                                # LOE rbx r12 r13 r14 r15
..B1.2:                         # Preds ..B1.10
        xorl      %esi, %esi                                    #17.15
        movq      16(%r14), %rdi                                #17.15
# double d2 = atof(argv[1]);をやってるところ
#       strtod(const char *, char **)
        call      strtod                                        #17.15
                                # LOE rbx r12 r13 r15 xmm0

# a.v[i] = d1, b.v[i] = d2をvbroadcastsdでやっている
..B1.3:                         # Preds ..B1.2
        vbroadcastsd %xmm0, %ymm2                               #17.15
        movl      $.L_2__STRING.0, %edi                         #26.5
        vbroadcastsd 32(%rsp), %ymm1                            #16.15
# 構造体の和はvaddpd一発
        vaddpd    %ymm2, %ymm1, %ymm3                           #24.3