The author is partly right here. If those values are ints, you'll get something like this:

  sar eax, 0x1f
  and eax, 7
  add eax, edx
  sar eax, 3

You get 4 instructions instead of one because value >> 3 rounds towards negative infinity and value / 8 rounds towards zero.

And while this wouldn't apply to C++, in languages with checked arithmetic, the left shift won't necessarily set the overflow flag, so the compiler often can't use it.

I wouldn't go that far, but yes, no compiler will leave that on the table today or even twenty years ago. They do even more impressive transformations than that on basic math.