[12] RFR: 8214059: Undefined behaviour in ADLC

[Aleksey Shipilev]

On 11/19/18 11:19 PM, Aleksey Shipilev wrote:
> I think the canonical way to perform overflow-sensitive addition involves checking against INT_MAX.
> Or, in this case, Expr::Max. Instead of this "long long" and STATIC_ASSERT mess, we can say:
> 
> int Expr::compute_max(const Expr *c1, const Expr *c2) {
>   int v1 = c1->_max_value;
>   int v2 = c2->_max_value;
> 
>   // Check for overflow without producing UB. If v2 is positive
>   // and not larger than Max, the subtraction cannot underflow.
>   assert(0 <= v2 && v2 <= Expr::Max, "sanity");
>   if (v1 > Expr::Max - v2) {
>     return Expr::Max;
>   }
> 
>   return v1 + v2;
> }

Also, Expr::compute_min seems to have the same problem, but not caught by sanitizer?

-Aleksey

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