overflows in SLDivNode

[Raffaello Giulietti]

I'm not an expert in machine code at all. However, my understanding is
that the x86_64 idiv instruction throws the same exception both when a
division by 0 occurs and also when the result overflows.

Since division by 0 in Java already throws an exception, one could
perhaps process an overflow in the same way in a hypothetical
intrinsified machine code implementation of divExact().

Or how does the machine code for a division by 0 look? Is the division
instruction guarded by a test on the divisor?

I'm asking the Graal people here...




On 2015-04-27 19:34, Chris Seaton wrote:
> Someone writing a Truffle language may look at the ExactMath class, see
> no exactDivide, and conclude that integer division cannot overflow. Even
> if our implementation does not give performance gains, it might be good
> to have it there so that they don’t assume this.
> 
> Chris
> 
>> On 27 Apr 2015, at 15:17, Andreas Woess <andreas.woess at oracle.com
>> <mailto:andreas.woess at oracle.com>> wrote:
>>
>> However, I don't think we should add a divExact method. We cannot
>> intrinsify it (the idiv instruction does not set the overflow flag);
>> for the same reason Java 8 does not have a divideExact. Also, the
>> utility method cannot specialize (whereas the SLDivNode can), so
>> having it does not buy us anything.
>