Suggestion for CP.201: Avoid volatile compound operations

CP.201 Limit use of volatile variables to loads and stores

Reason

• Compilers don't agree on whether compound operations should be split up, which makes our code less portable. This distinction is very important when working with volatile memory.
• Compound operations other than compound assignment are deprecated for volatile.

Example

volatile uint32_t counter;

void update()
{
    counter++; // bad, is this in-place increment, or a separate read, add, and write?
               // the difference matters for volatile access!

    auto x = counter; // good, this is always a read, modify, and write
    counter = x + 1;
}

Alternative

Create convenience functions for compound volatile operations, and implement them using explicit loads and stores.

Enforcement

Flag compound operations on volatile variables.

No file or test entry point is named. Start by locating the CP.201 guideline and the project's enforcement mechanisms, then determine how compound operations on volatile variables are identified; done means the rule and its enforcement behavior cover the stated cases.