The problem here isn't updateCachedWidth(), which indeed modifies a member variable, but deviceScaleFactor(), which doesn't. Since LLVM doesn't infer that deviceScaleFactor() leaves m_cachedWidth unmodified, it forces a reload of m_cachedWidth after the function call in case the value changed.
It was an example. Replace deviceScaleFactor with some other function that modifies, say, m_foo, and you have the same problem. And no, const+mutable is not an answer(in my example), because the function does in fact modify the class in a way important to the caller.
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The problem here isn't updateCachedWidth(), which indeed modifies a member variable, but deviceScaleFactor(), which doesn't. Since LLVM doesn't infer that deviceScaleFactor() leaves m_cachedWidth unmodified, it forces a reload of m_cachedWidth after the function call in case the value changed.
It was an example. Replace deviceScaleFactor with some other function that modifies, say, m_foo, and you have the same problem. And no, const+mutable is not an answer(in my example), because the function does in fact modify the class in a way important to the caller.