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0 pointsE63009y ago0 comments

On the other hand, the expected and desirable behavior in one platform might be different from that in another platform. It's possible to overspecify and end up requiring extra code when performing ordinary arithmetic operations, or lock yourself out of useful optimizations.

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sjolsen9y ago

Which is exactly the motivation behind implementation-defined behavior. There's a broad range of "how much detail do you put in the specification" between the extremes of "this is exactly how the program should behave" and "this program fragment is ill-formed, therefore we make no guarantees about the behavior of the overall program whatsoever."

E6300OP9y ago

Implementation-defined behavior at best just tells you that the behavior is guaranteed to be deterministic (or not). You still cannot reason about the behavior of the program by just looking at the source.

And I'm not sure if optimizations such as those that require weak aliasing would be possible if the behavior was simply implementation-defined.

sjolsen9y ago

The desire to reason about the precise behavior of a program and the desire to take advantage of different behavior on different platforms are fundamentally at odds. Like I said, there's a broad range of just how much of the specification you leave up to the implementation; it's an engineering trade-off like any other.

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0 pointsE63009y ago0 comments

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sjolsen9y ago

E6300OP9y ago

And I'm not sure if optimizations such as those that require weak aliasing would be possible if the behavior was simply implementation-defined.

sjolsen9y ago

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