Why doesn't a compiler optimize floating-point *2 into an exponent increment?

Question

I\'ve often noticed gcc converting multiplications into shifts in the executable. Something similar might happen when multiplying an int and a float. F

Answer 1

Here's an actual compiler optimization I'm seeing with GCC 10:

x = 2.0 * hi * lo;

Generates this code:

mulsd   %xmm1, %xmm0      # x = hi * lo;
addsd   %xmm0, %xmm0      # x += x;