A single historical context of volatile

"... any object ... of a volatile-qualified type should not participate in optimizations that would ... modif[y] the object."

To my mind that prohibition includes non-volatile object optimizations that would clobber volatile objects.

The book then slightly contradicts itself two paragraphs later by saying that "optimizations between sequence points are permitted" before clarifying with a hardware example.

* A standard ANSI C reference manual for programmers and compiler implementers at the time.