问为什么Clang会优化x* 1.0而不是x+ 0.0？

EN

#include <time.h>
#include <stdio.h>

static size_t const N = 1 << 27;
static double arr[N] = { /* initialize to zero */ };

int main()
{
    clock_t const start = clock();
    for (int i = 0; i < N; ++i) { arr[i] *= 1.0; }
    printf("%u ms\n", (unsigned)(clock() - start) * 1000 / CLOCKS_PER_SEC);
}

#include <time.h>
#include <stdio.h>

static size_t const N = 1 << 27;
static double arr[N] = { /* initialize to zero */ };

int main()
{
    clock_t const start = clock();
    for (int i = 0; i < N; ++i) { arr[i] += 0.0; }
    printf("%u ms\n", (unsigned)(clock() - start) * 1000 / CLOCKS_PER_SEC);
}