What kinds of optimizations does ‘volatile’ prevent in C++?

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Basically, volatile announces that a value might change behind your program’s back. That prevents compilers from caching the value (in a CPU register) and from optimizing away accesses to that value when they seem unnecessary from the POV of your program.

What should trigger usage of volatile is when a value changes despite the fact that your program hasn’t written to it, and when no other memory barriers (like mutexes as used for multi-threaded programs) are present.

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