NagyDonat wrote: > > [...] This different sort of limitation still guarantees that we cannot > > build overly complex symbols, but its implementation is significantly > > shorter (just three early return statements for unary operator, binary > > operator and cast evaluation). > > 💡 In fact, you can compare the threshold with the sum of complexity values > > of the two operands to get a heuristic which is practically equivalent to > > the complexity threshold that you want, but doesn't pass around > > `UnknownVal`s in already complex code and doesn't introduce a new symbol > > kind. > > I played with the idea and there is one wrinkle. EvalBinOp applies tactics > that can reduce the requested operation to known values or ranges after > applying some logic, like: > > * eagerly fold away multiplications to 1 > > * shifting 0 left or right to a cast > > * zero divided/modulo by some value to 0 > > * others > > > By checking the sum of the operand complexities before applying these > heuristics would mean that we would lose out on these benefits, thus reduce > cases into `Unknown` while in the past we could have deduced a simple result > for the case. The evalbinops use a bunch of APIs (call `makeSymExprValNN`, > `makeNonLoc`, etc), so it's not easy to ensure that on all paths we obey the > max complexity rule - unless we do the complexity check at `makeNonLoc`, > where everything boils down to. > > This was the originally proposed version, which was rejected due to the fact > that if `makeNonLoc` could return `Unknown` then a bunch of call-sites would > need to be updated to accommodate for this. > > So, I think if we go with the evalbinop approach, then it should work as > efficiently as my original proposal, while sacreficing the special cases that > fold away the binop. I'm fine with either of the approaches. I scheduled a > measurement for the evalbinop approach, and I expect the results by tomorrow > the latest.
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