Interval: Don't compute on top values #134
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Arithmetic operations on the current top representation of the interval domain now return top if any of the operands is top. The reason is that the top value [-2^31,2^31-1] is too "narrow" to represent some concrete values. Thus computing with it leads to spurious, unsound results.
Loss in precision is due to no longer computing with top in the interval domain.
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This introduces a fix so we no longer compute on
topvalues within the interval domain.The
topin the interval is actually represented by the interval[-2^31, 2^31-1]. As the concrete values for a integer might lie outside this range, we cannot compute with this value, because this could yield unsound results. So instead, if one of the operands of a binary/unary operation istop, the result of the operation will betop, too.Side note: Having a top value in an interval representation that is truly an over-approximation for all possible concrete values (including
-2^63,2^64-1) would require an implementation with arbitrary precision integers.